Meiosis

To start determining the nature of meiotic incompetence in goat oocytes, we have examined the expression of one of the potential pre-MPF subunits: the cyclin B 1 . We have been isolating a small DNA probe encoding the goat cyclin B 1 box to analyze the expression of the cyclin B 1 gene in competent and incompetent goat oocytes. This probe was easily obtained by polymerase-chain-reaction (PCR) on reversetranscribed mRNA from granulosa cells, using cyclin B specific primers derived from a bovine cDNA. The transcript corresponding to cyclin B 1 in goat granulosa cells is 1.8 kb. In situ hybridization analysis indicated that competent and incompetent oocytes contained cyclin B 1 mRNA, but also that active cyclin B 1 mRNA synthesis occured at the end of the growth phase, e.g., when oocytes progressed in the acquisition of meoitic competence. Western blot analysis, performed with a monoclonal anticyclin B 1 antibody, revealed in competent and incompetent oocytes a polypeptide of 65kDa corresponding to the goat cyclin B 1 protein. This pattern of cyclin B 1 expression further suggested that meiotic incompetence in goat oocytes could not be primarily correlated with a lack of cyclin B 1 protein as potential pre-MPF subunit, but to a limiting amount of this protein. Mol. Reprod. Dev. 47:222-228, 1997. r 1997 Wiley-Liss, Inc.

The GLH proteins belong to a family of four germline RNA helicases in Caenorhabditis elegans. These putative ATP-dependent enzymes localize to the P granules, which are nonmembranous complexes of protein and RNA exclusively found in the cytoplasm of all C. elegans germ cells and germ cell precursors. To determine what proteins the GLHs bind, C. elegans cDNA libraries were screened by the yeast two-hybrid method, using GLHs as bait. Three interacting proteins, CSN-5, KGB-1, and ZYX-1, were identified and further characterized. GST pull-down assays independently established that these proteins bind GLHs. CSN-5 is closely related to the subunit 5 protein of COP9 signalosomes, conserved multiprotein complexes of plants and animals. RNA interference (RNAi) with csn-5 results in sterile worms with small gonads and no oocytes, a defect essentially identical to that produced by RNAi with a combination of glh-1 and glh-4. KGB-1 is a putative JNK MAP kinase that GLHs bind. A kgb-1 deletion strain has a temperature-sensitive, sterile phenotype characterized by the absence of mature oocytes and the presence of trapped, immature oocytes that have undergone endoreplication. ZYX-1 is a LIM domain protein most like vertebrate Zyxin, a cytoskeletal adaptor protein. In C. elegans, while zyx-1 appears to be a single copy gene, neither RNAi depletion nor a zyx-1 deletion strain results in an obvious phenotype. These three conserved proteins are the first members in each of their families reported to associate with germline helicases. Similar to the loss of GLH-1 and GLH-4, loss of either CSN-5 or KGB-1 causes oogenesis to cease, but does not affect the initial assembly of P granules. © 2002 Elsevier Science (USA)

We have discovered that single-stranded DNA containing short guanine-rich motifs will self-associate at physiological salt concentrations to make four-stranded structures in which the strands run in parallel fashion. We believe these complexes are held together by guanines bonded to each other by Hoogsteen pairing. Such guanine-rich sequences occur in immunoglobulin switch regions, in gene promoters, and in chromosomal telomeres. We speculate that this self-recognition of guanine-rich motifs of DNA serves to bring together, and to zipper up in register, the four homologous chromatids during meiosis.

In this review, the pathways involving small RNAs are provided followed by a new and updated network that illustrates their interplay with diverse cellular mechanisms in Caenorhabditis elegans. The RNA silencing pathways are now recognized as key factors that connect together the many variations in biological processes, including transcriptional gene regulation, post-transcriptional gene silencing, translational gene silencing, apoptosis, meiosis, and antiviral defense. The utilization of small RNAs represents a specific, energy conserving, and fast mechanism of gene regulation via a core system known as RNA interference.

The objective of this study was to determine the influence of powdered coconut water (ACP-318®) diluted in high glucose (11.0 mm) TCM199 in the achievement of nuclear in vitro maturation (IVM) of canine oocytes. Cumulus oocyte complexes (COCs) (n = 632) were randomly allocated into three experimental groups named as group 1 (control group), group 2 (5% powdered coconut water) and group 3 (10% powdered coconut water). The percentage of meiotic resumption (MR) (GVBD to MII) was 39.1% (81/207), 50.2% (108/215) and 46.6% (98/210) for groups 1, 2 and 3 respectively (p < 0.05). There were no differences in MR rates among groups 2 and 3. The medium with ACP-318® slightly enhanced the nuclear maturation of canine oocytes when a comparison was established with rates of maturation exhibited by oocytes in the experimental group 1 without ACP-318® (p < 0.05). The results suggest that oocytes’ nuclear morphology integrity and meiosis achievement were positively influenced when exposed to high glucose TCM199 supplemented with 5% powdered coconut water. Further investigation must be performed for a better understanding of powdered coconut water influence in cellular events during IVM of dog oocytes.

The Schizosaccharomyces pombe Mei2 gene encodes an RNA recognition motif (RRM) protein that stimulates meiosis upon binding a specific non-coding RNA and subsequent accumulation in a "mei2-dot" in the nucleus. We present here the first systematic characterization of the family of proteins with characteristic Mei2like amino acid sequences. Mei2-like proteins are an ancient eukaryotic protein family with three identifiable RRMs. The C-terminal RRM (RRM3) is unique to Mei2like proteins and is the most highly conserved of the three RRMs. RRM3 also contains conserved sequence elements at its C-terminus not found in other RRM domains. Single copy Mei2-like genes are present in some fungi, in alveolates such as Paramecium and in the early branching eukaryote Entamoeba histolytica, while plants contain small families of Mei2-like genes. While the C-terminal RRM is highly conserved between plants and fungi, indicating conservation of molecular mechanisms, plant Mei2-like genes have changed biological context to regulate various aspects of developmental pattern formation.

In budding yeasts, the histone deacetylase Rpd3 resides in two different complexes called Rpd3L (large) and Rpd3S (small) that exert opposing effects on the transcription of meiosis-specific genes. By introducing mutations that disrupt the integrity and function of either Rpd3L or Rpd3S, we show here that Rpd3 function is determined by its association with either of these complexes. Specifically, the catalytic activity of Rpd3S activates the transcription of the two major positive regulators of meiosis, IME1 and IME2, under all growth conditions and activates the transcription of NDT80 only during vegetative growth. In contrast, the effects of Rpd3L depends on nutrients; it represses or activates transcription in the presence or absence of a nitrogen source, respectively. Further, we show that transcriptional activation does not correlate with histone H4 deacetylation, suggesting an effect on a nonhistone protein. Comparison of rpd3-null and catalytic-site point mutants revealed an ...

BACKGROUND: The aim of our study was to evaluate the possibility of embryonic or somatic cell haploidization after fusion with intact or enucleated immature oocytes which were subsequently cultured in vitro. Embryonic or somatic cell nuclei do not undergo premature chromosome condensation when fused to intact or enucleated immature oocytes whose maturation is prevented by dibutyryl cyclic AMP (dbcAMP). The presence of dbcAMP permits, however, the completion of DNA replication in somatic cell nuclei. METHODS AND RESULTS: The chromosomes condensed when the reconstructed cells were released from the dbcAMP block. When somatic or embryonic nuclei were introduced into intact immature meiotically competent oocytes and subsequently cultured their chromosomes assembled on a common spindle with meiotic chromosomes and proceeded through the meioticlike division, judged according to the presence of the first polar body extruded. When embryonic cell nuclei were introduced into cytoplasts obtained from immature meiotically competent oocytes, polar bodies were extruded in about 75% of reconstructed cells but the metaphase plates were abnormal in almost all cases. When somatic cell nuclei were inserted into the above cytoplasts, polar bodies were extruded only very exceptionally and in these cells chromosomes were arranged in abortive metaphase plates. CONCLUSIONS: Our results suggest that somatic cell nuclei are unable to proceed through the reduction division (haploidization) when introduced into an immature oocyte meiotic cytoplasm.

This article describes the first successful induction of meiotic gynogenesis in Wels catfish (Silurus glanis) using heterologous sperm of grass carp (Ctenopharyngodon idella) with DNA inactivated by means of UV-irradiation at 4800 J/m 2. The cold shock at 61C (duration of 20 min) started in the nineth minute after fertilization was found as efficient in retaining the second polar body and producing meiotic diploids. Successful induction of meiotic gynogenesis was confirmed by the microsatellite DNA analysis, which revealed only maternal inheritance in gynogenetic offspring. Ploidy of gynogenetic offspring was verified by the application of active nucleoli counting analysis.

Preferential chromosome association at metaphase I has been analyzed and compared in autotetraploid cells obtained by colchicine treatment of hybrid diploid rye plants with different degrees of chromosomal divergence between homologs. The tendency to identical over homologous, but not identical, pairing preferences detected when homologous partners are contributed by less related parental lines indicates that chromosome differentiation may play an important role on preferential pairing behavior of polyploids. However, associations between more similar (identical) partners are not always favored, thus suggesting that additional factors must be considered. Other hypotheses for explaining pairing preferences in competitive situations are discussed. No clear relationship has been found between multivalent frequencies at metaphase I and chromosome differentiation between homologs or preferential pairing behavior. Therefore evolutionary divergences among related genomes should be carefull...

he fruit fly (Drosophila melanogaster) is an ideal subject for studying inheritance patterns, Mendel's laws, meiosis, Punnett squares, and other aspects of genetics. Much of what we know about genetics dates to evolutionary biologist Thomas Hunt Morgan's work with mutated fruit flies in the early 1900s (DNA Learning Center 2011). Many genetic laboratories throughout the world still use fruit flies today (Carlson 2004). Fruit flies are sometimes used in the classroom, but because live stocks can be difficult to maintain, we developed an activity that substitutes fruit fly cards for live fruit flies. This article describes how to make these cards and implement the activity, which aligns with the Next Generation Science Standards (NGSS Lead States 2013; see box, p. 47).

An idea is a thought that generates in the mind. It is a notion that exist in the mind as a representation or formulation. Usually thought is generated by one observation or the other in the environment, and this observation is always termed “issue” challenges or what you will. As long as there are issues of concern in the environment there will be ideas notions and formulations conceived and postulated into concept. In science this type of concept is termed an invention or innovation. Such innovation may remain without a brand name or not, such a case is a brand name now termed Quantum Biology.
The idea of quantum Biology is old as molecular Biology’s idea because one completes the other. Quantum is a term that may seem alien to Biology because it is more much applied in physics and Chemistry, forgetting that Biology is a member of this family of science. This particular observation had been made decades ago by some other versatile scientist who have advocated for it literally and numerically. The wise say: no army can stop an idea whose time has come” probably this is the time of quantum Biology.

The organisation of chromatin is non-random and shows a broad diversity across cell types, developmental stages, and cell cycle stages. During G0 and G1 phase of interphase, chromatin displays a bivalent status. The condensed chromatin (heterochromatin) at the nuclear periphery is mostly associated with low levels of gene expression, while the loosened chromatin (euchromatin) towards the interior of the nucleus is associated with higher gene expression. This quiescent picture of interphase radically changes when the cell cycle progresses toward cell division. Firstly, during S phase, DNA is replicated, and chromatin progressively condenses. This is followed by the G2 phase that shows a compact heterochromatin recruited towards the centre of the nucleus. At the beginning of mitosis, the chromosomes condense with a significant topological change in their organisation and are segregated during the next stages of the cell division. Meiotic chromosomes are also highly condensed as mitotic chromosomes but show a particular functional structure, which prepares germ cells to exchange DNA sequences between their homologous chromosomes to generate diversity. To summarise, chromatin experiences dramatic organisational changes during mitosis and meiosis. These changes in chromatin organisation during the lifetime of a cell show that chromatin is not a static entity but highly dynamic in nature.

For a variety of reasons, conventional light and electron microscopy have not been able to fully capture the finer details of chromatin organisation and dynamics. For a long time, description of the interphase nucleus was limited to delineate the euchromatin-heterochromatin dichotomy or describe some specific nuclear elements such as the nucleolus. Advancements in molecular biology during the last thirty years have brought an immense amount of information about how chromatin is organised and genes are regulated. As a classical example, the globin gene has been shown to display a highly constrained shape forced by chromatin looping that brings the regulatory regions to the promoter of the gene. Nowadays, genomic studies can acquire an immense amount of information regarding chromatin organisation and gene regulation, leaving one with the expectation that structure of individual genes could potentially be described visually if sufficient specificity and resolution were reached. With the advent of various super-resolution methods, in particular, single molecule localisation microscopy (SMLM) based methods and recently developed strategies for labelling DNA, it is now possible to study chromatin organisation and underlying gene regulatory mechanisms at the nanoscale.

During my PhD, I have analysed a broad range of nuclear phenotypes using SMLM. My analyses contribute to the description of a periodic and dynamic structure of chromatin. Moreover, I have described several elementary chromatin structures that I call chromatin domains, both in interphase and meiosis, that are potentially associated with a local function such as gene activation or silencing.

Firstly with colleagues, I established an experimental setup to study chromatin organisation with single molecule localisation microscopy. I investigated how UV-induced photo-conversion of conventional DNA dyes allows increasing sufficiently the labelling density such that it is possible to study various organisational aspects of chromatin in basal interphase. An adequate imaging protocol has been established to bring DNA minor groove binding dyes such as Hoechst 33258, Hoechst 33342 and DAPI (4’,6-diamidino-2-phenylindole) into an efficient blinking state necessary to record single molecule locations with high precision. This method was applied to several cell types to investigate the chromatin organisation during different stages of the cell cycle at the highest resolution currently achievable with light microscopy.

The results show that the method can capture several hierarchical levels of chromatin organisation. In reverse hierarchical order, I could describe previously known chromatin territories of 1000 nm, subchromosomal domains of 500 nm, chromatin domains of 100 to 400 nm (and further sub-categories of active or repressed domains) and chromatin fibres below 100 nm, mostly between 30 to 60 nm. Individual nucleosomal domains are also described, which tend to cluster in batches of 10-15 nucleosomes, a number close to one found in genomic studies upstream to promoter regions. Next, with colleagues, I studied the dynamics of chromatin using stress as a model system. It was found that short-term oxygen and nutrient deprivation provokes chromatin to shrink to a hollow, condensed ring and rod-like configuration, which reverses back to the initial structure when the stress conditions cease. The condensed network of rods and rings interspersed with large, chromatin-sparse nuclear voids were 40-700 nm in dimension, capturing another level of chromatin organisation not described before.

Finally, I explored the unique properties of chromatin during meiosis, which has escaped analysis at the single-molecule level until now. Single molecule analysis revealed unexpected highly recognisable periodic patterns of chromatin. Firstly, I observed that meiotic chromatin show unique clusters of 250 nm diameter along the synaptonemal complex, extended laterally by chromatin fibres forming loops. These clusters show a remarkable periodicity of 500 nm, a pattern possible to spot because of the highly deterministic nature of pachytene chromosomes and the resolution of the experimental setup. Furthermore, guided by genomic data, I selected histone modifications associated with different chromatin states to dissect the morphology of meiotic chromosomes. I could examine the morphology of these chromosomes into three spatially distinct nanoscale sub-compartments. Histone mark H3K4me3 associated with active chromatin was found in a lateral position, potentially located at the places of de novo double-strand breaks. Repressive histone mark H3K27me3 was shown to display a surprising medial symmetrical and periodic pattern, putatively associated with recombination. Finally, centromeric histone mark H3K9me3 locates at one of meiotic chromosome ends and is potentially associated with repression of repeated regions and pairing of homologous chromosomes at early stages. I summarise these findings in a comprehensive final model.

Overall, I have used new information brought by super-resolution technologies to show the dynamics of chromatin in various processes and novel orders of chromatin compaction, which were not reported previously. Among these new levels of chromatin compaction are the interphase hierarchical chromatin domains, the stress pattern of cells upon oxygen and nutrients deprivation and the novel epigenetic domains found at pachytene stage of meiosis. These architectures show that the organisation of chromatin is more complex than thought before, dynamic in nature and shows a high order of periodicity. Further investigation is, therefore, necessary to understand how chromatin transits from a ’beads-on-string’ model to the intermediary chromatin domains and finally to the commonly observed X-shaped chromosomes.

Compared to the diversity of other floral organs, the steps in anther ontogeny, final cell types, and overall organ shape are remarkably conserved among Angiosperms. Defects in pre-meiotic anthers that alter cellular composition or function typically result in male-sterility. Given the ease of identifying male-sterile mutants, dozens of genes with key roles in early anther development have been identified and cloned in model species, ordered by time of action and spatiotemporal expression, and used to propose explanatory models for critical steps in cell fate specification. Despite rapid progress, fundamental issues in anther development remain unresolved, and it is unclear if insights from one species can be applied to others. Here we construct a comparison of Arabidopsis, rice, and maize immature anthers to pinpoint distinctions in developmental pace. We analyze the mechanisms by which archesporial (pre-meiotic) cells are specified distinct from the soma, discuss what constitutes ...

F(1) backcrosses involving the DDK and C57BL/6 inbred mouse strains show transmission ratio distortion at loci on two different chromosomes, 11 and X. Transmission ratio distortion on chromosome X is restricted to female offspring while that on chromosome 11 is present in offspring of both sexes. In this article we investigate whether the inheritance of alleles at loci on one chromosome is independent of inheritance of alleles on the other. A strong nonrandom association between the inheritance of alleles at loci on both chromosomes is found among male offspring, while independent assortment occurs among female offspring. We also provide evidence that the mechanism by which this phenomenon occurs involves preferential cosegregation of nonparental chromatids of both chromosomes at the second meiotic division, after the ova has been fertilized by a C57BL/6 sperm bearing a Y chromosome. These observations confirm the influence of the sperm in the segregation of chromatids during female...

One of the most prospective directions of study of C.G. Jung’s synchronicity phenomenon
is reviewed considering the latest achievements of modern science. The attention is
focused mainly on the quantum entanglement and related phenomena – quantum
coherence and quantum superposition. It is shown that the quantum non-locality capable
of solving the Einstein-Podolsky-Rosen paradox represents one of the most adequate
physical mechanisms in terms of conformity with the Jung’s synchronicity hypothesis. An
attempt is made on psychophysiological substantiation of synchronicity within the context
of molecular biology. An original concept is proposed, stating that biological molecules
involved in cell division during mitosis and meiosis, particularly DNA may be considered
material carriers of consciousness. This assumption may be formulated on the basis of
phenomenology of Jung’s analytical psychology

TEORIA CELULAR: "La materia viva consiste de células" "Las reacciones químicas de un organismo vivo tienen lugar dentro de las células" "Las células se originan a partir de otras células" "Las células contienen información hereditaria de los organismos que forman parte y esta información se transmite de la célula madre a la célula hija" TEORIA DE LA EVOLUCION: "Las distintas especies están emparentadas y proceden de un antepasado común, aunque los detalles de cómo ocurrió sean cuestionados"

Although a number of genes that play key roles during the meiotic process have been characterized in great detail, the whole process of meiosis is still not completely unraveled. To gain insight into the bigger picture, large-scale approaches like RNA-seq and microarray can help to elucidate the transcriptome landscape during plant meiosis, discover co-regulated genes, enriched processes, and highly expressed known and unknown genes which might be important for meiosis. These high-throughput studies are gaining more and more popularity, but their beginnings in plant systems reach back as far as the 1960&#39;s. Frequently, whole anthers or post-meiotic pollen were investigated, while less data is available on isolated cells during meiosis, and only few studies addressed the transcriptome of female meiosis. For this review, we compiled meiotic transcriptome studies covering different plant species, and summarized and compared their key findings. Besides pointing to consistent as well ...

Chromosome missegregation in germ cells is an important cause of unexplained infertility, miscarriages, and congenital birth defects in humans. However, the molecular defects that lead to production of aneuploid gametes are largely unknown. Cdc20, the activating subunit of the anaphase-promoting complex/cyclosome (APC/C), initiates sister-chromatid separation by ordering the destruction of two key anaphase inhibitors, cyclin B1 and securin, at the transition from metaphase to anaphase. The physiological significance and full repertoire of functions of mammalian Cdc20 are unclear at present, mainly because of the essential nature of this protein in cell cycle progression. To bypass this problem we generated hypomorphic mice that express low amounts of Cdc20. These mice are healthy and have a normal lifespan, but females produce either no or very few offspring, despite normal folliculogenesis and fertilization rates. When mated with wild-type males, hypomorphic females yield nearly normal numbers of fertilized eggs, but as these embryos develop, they become malformed and rarely reach the blastocyst stage. In exploring the underlying mechanism, we uncover that the vast majority of these embryos have abnormal chromosome numbers, primarily due to chromosome lagging and chromosome misalignment during meiosis I in the oocyte. Furthermore, cyclin B1, cyclin A2, and securin are inefficiently degraded in metaphase I; and anaphase I onset is markedly delayed. These results demonstrate that the physiologically effective threshold level of Cdc20 is high for female meiosis I and identify Cdc20 hypomorphism as a mechanism for chromosome missegregation and formation of aneuploid gametes.

Missegregation of chromosomes in meiosis, or nondisjunction, occurs relatively frequently in humans, and results in pregnancy loss. There is a correlation with advancing maternal age, but the cause of the dramatic increase of aneuploidy, and specifically trisomy (the presence of three copies of a chromosome rather then two), seen with age remains unknown. There is evidence to suggest that chronological age is less important than biological age for trisomy risk, and that regardless of their chronological age, some women are at a greater risk of having a trisomic pregnancy after having already experienced one. Several features of chromosomes are associated with aging, such as a decrease in telomere length, an increase in replication asynchrony at loci including centromeres, and an increase in somatic cell aneuploidy with increasing age. For some chromosomes (15 and 21) an association has also been observed between maternal age, reduced recombination along the chromosome, and risk for nondisjunction. In this project, I have investigated whether or not some women are predisposed to having a trisomic pregnancy. That is, can we predict who will have recurrent trisomy? After analyzing telomere length for an association, no significant decrease in length was seen for women experiencing recurrent trisomy when compared to control women. There was a trend, however, towards longer telomeres in women with a "good" reproductive history (children after 37 years of age) compared to women with a "poor" reproductive history (trisomy and/or recurrent trisomy). As well, although there was no significant increase in replication asynchrony in mothers of trisomy as a group, the younger mothers (<35 years old) of trisomies had increased replication asynchrony when compared to controls of the same age. The relationship between recombination and nondisjunction has been well established and my studies of chromosome 15 confirmed that decreased recombination is associated with meiosis I errors and increased recombination is associated with meiosis II errors. A family with an apparent inherited predisposition to missegregation of chromosome 21 seemed the ideal family in which to study possible genetic mechanisms of nondisjunction. Although nothing conclusive could be determined to be causing their segregation problems, a cryptic rearrangement involving the centromere of chromosome 21 is the most likely explanation. Finally, telomere length was not found to be shortened in children conceived through intracytoplasmic sperm injection (ICSI).

Here, we outline the mechanisms involved in the regulation of cell divisions during oocyte maturation and early cleavages of the mouse embryo. Our interest is focused on the regulation of meiotic M-phases and the first embryonic mitoses that are differently tuned and are characterized by specifically modified mechanisms, some of which have been recently identified. The transitions between the M-phases during this period of development, as well as associated changes in their regulation, are of key importance for both the meiotic maturation of oocytes and the further development of the mammalian embryo. The mouse is an excellent model for studies of the cell cycle during oogenesis and early development. Nevertheless, a number of molecular mechanisms described here were discovered or confirmed during the study of other species and apply also to other mammals including humans.

DNA topoisomerase VI from Archaea, a heterotetrameric complex composed of two TopVIA and two TopVIB subunits, is involved in altering DNA topology during replication, transcription and chromosome segregation by catalyzing DNA strand transfer through transient double-strand breaks. The sequenced yeast and animal genomes encode only one homologue of the archaeal TopVIA subunit, namely Spo11, and no homologue of the archaeal TopVIB subunit. In yeast, Spo11 is essential for initiating meiotic recombination and this function appears conserved among other eukaryotes. In contrast to yeast and animals, studies in Arabidopsis and rice have identified three Spo11/TopVIA homologues and one TopVIB homologue in plants. Here, we further identified two novel Spo11/TopVIA homologues (named OsSpo11-4 and OsSpo11-5, respectively) that exist just in the monocot model plant Oryza sativa, indicating that at least five Spo11/TopVIA homologues are present in the rice genome. To reveal the biochemical function of the two novel Spo11/TopVIA homologues, we first examined the interactions among OsSpo11-1, OsSpo11-4, OsSpo11-5, and OsTopVIB by yeast two-hybrid assay. The results showed that OsSpo11-4 and OsTopVIB can self-interact strongly and among the 3 examined OsSpo11 proteins, only OsSpo11-4 interacted with OsTopVIB. Pull-down assay confirmed the interaction between OsSpo11-4 and OsTopVIB, which indicates that OsSpo11-4 may interact with OsTopVIB in vivo. Further in vitro enzymatic analysis revealed that among the above 4 proteins, only OsSpo11-4 exhibited double-strand DNA cleavage activity and its enzymatic activity appears dependent on Mg 2+ and independent of OsTopVIB, despite its interaction with OsTopVIB. We further analyzed the biological function of OsSpo11-4 by RNA interference and found that down-regulated expression of OsSpo11-4 led to defects in male meiosis, indicating OsSpo11-4 is required for meiosis.

The rice (Oryza sativa) genome contains 18 copies of genes of the ARGONAUTE (AGO) family. Although AGO members play important roles in RNA-mediated silencing during plant development, a family member that is specifically involved in sexual reproduction has not been identified in plants. We identified the rice AGO gene MEIOSIS ARRESTED AT LEPTOTENE1 (MEL1) from the analysis of seed-sterile mutants. In the mel1 mutant, chromosome condensation was arrested at early meiotic stages and irregularly sized, multinucleated, and vacuolated pollen mother cells (PMCs) frequently appeared in developing anthers. In addition, histone H3 lysine-9 dimethylation of pericentromeres was rarely reduced and modification of the nucleolarorganizing region was altered in mel1 mutant PMCs. The mutation also affected female germ cell development. These results indicate that the germ cell-specific rice MEL1 gene regulates the cell division of premeiotic germ cells, the proper modification of meiotic chromosomes, and the faithful progression of meiosis, probably via small RNA-mediated gene silencing, but not the initiation and establishment of germ cells themselves.

MUS81 is conserved among plants, animals, and fungi and is known to be involved in mitotic DNA damage repair and meiotic recombination. Here we present a functional characterization of the Arabidopsis thaliana homolog AtMUS81, which has a role in both mitotic and meiotic cells. The AtMUS81 transcript is produced in all tissues, but is elevated greater than 9-fold in the anthers and its levels are increased in response to gamma radiation and methyl methanesulfonate treatment. An Atmus81 transfer-DNA insertion mutant shows increased sensitivity to a wide range of DNA-damaging agents, confirming its role in mitotically proliferating cells. To examine its role in meiosis, we employed a pollen tetrad-based visual assay. Data from genetic intervals on Chromosomes 1 and 3 show that Atmus81 mutants have a moderate decrease in meiotic recombination. Importantly, measurements of recombination in a pair of adjacent intervals on Chromosome 5 demonstrate that the remaining crossovers in Atmus81 are interference sensitive, and that interference levels in the Atmus81 mutant are significantly greater than those in wild type. These data are consistent with the hypothesis that AtMUS81 is involved in a secondary subset of meiotic crossovers that are interference insensitive.

Maize anther ontogeny is complex, with the expression of more than 30 000 genes over 4 days of cell proliferation, cell fate acquisition and the start of meiosis. Although many male-sterile mutants disrupt these key steps, few have been investigated in detail. The terminal phenotypes of Zea mays (maize) male sterile 8 (ms8) are small anthers exhibiting meiotic failure. Here, we document much earlier defects: ms8 epidermal cells are normal in number but fail to elongate, and there are fewer, larger tapetal cells that retain, rather than secrete, their contents. ms8 meiocytes separate early, have extra space between them, occupied by excess callose, and the meiotic dyads abort. Thousands of transcriptome changes occur in ms8, including ectopic activation of genes not expressed in fertile siblings, failure to express some genes, differential expression compared with fertile siblings and about 40% of the differentially expressed transcripts appear precociously. There is a high correlation between mRNA accumulation assessed by microarray hybridization and quantitative real-time reverse transcriptase polymerase chain reaction. Sixty-three differentially expressed proteins were identified after two-dimensional gel electrophoresis followed by liquid chromatography tandem mass spectroscopy, including those involved in metabolism, plasmodesmatal remodeling and cell division. The majority of these were not identified by differential RNA expression, demonstrating the importance of proteomics in defining developmental mutants.

DMCl/LIM15 homologue 1 (D L H l) , a gene related to meiosis-specific genes, has been isolated from Candida albicans, a fungus thought not to undergo meiosis. The deduced protein sequence of DLHl contains 74% amino acid identity with Dmclp from Saccharomyces cermisiae and 63% with Liml5p from the plant Lilium long)lmm, meiosisspecific homologues of Escherichia coli R e d. Candida DLHl complements a dmcl/dmcl null mutant in S. cermisiae: High copy expression of DLHl restores both sporulation and meiotic recombination to a Saccharomyces dmclA/dmclA strain. Unlike the DMCl gene, which is transcribed only in meiotic cells, the heterologous Candida DLHl gene is transcribed in both vegetative and meiotic cells of S. cermisiae. Transcription of DLHl is not detected or induced in C. albicans under conditions that induce DMCl and meiosis in S. cermisiae. The presence of an intact homologue of a meiosis-specific gene in C. albicans raises the possibility that this organism has a cryptic meiotic pathway.

Male fertility in flowering plants depends on proper cellular differentiation in anthers. Meiosis and tapetum development are particularly important processes in pollen production. In this study, we showed that the tomato male sterile (ms10 (35) ) mutant of cultivated tomato (Solanum lycopersicum) exhibited dysfunctional meiosis and an abnormal tapetum during anther development, resulting in no pollen production. We demonstrated that Ms10 (35) encodes a basic helix-loop-helix transcription factor that is specifically expressed in meiocyte and tapetal tissue from pre-meiotic to tetrad stages. Transgenic expression of the Ms10 (35) gene from its native promoter complemented the male sterility of the ms10 (35) mutant. In addition, RNA-sequencing-based transcriptome analysis revealed that Ms10 (35) regulates 246 genes involved in anther development processes such as meiosis, tapetum development, cell-wall degradation, pollen wall formation, transport, and lipid metabolism. Our results i...

The tapetum, the innermost of four sporophytic layers in the anther wall, comes in direct contact with the developing male gametophyte and is thought to play a crucial role in the development and maturation of microspores. Here, we report the identification of rice (Oryza sativa) Undeveloped Tapetum1 (Udt1), which is required for the differentiation of secondary parietal cells to mature tapetal cells. T-DNA or retrotransposon Tos17 insertions in the Udt1 gene caused male sterility. The anther walls and meiocytes of the mutants were normal during the early premeiosis stage, but their tapeta failed to differentiate and became vacuolated during the meiotic stage. In addition, meiocytes did not develop to microspores, and middle layer degeneration was inhibited. Consequently, the anther locules contained no pollen. The UDT1:green fluorescent protein fusion protein was localized to the nucleus. This, together with its homology with other basic helix-loop-helix proteins, suggests that UDT1 is a transcription factor. DNA microarray analysis identified 958 downregulated and 267 upregulated genes in the udt1-1 anthers, suggesting that Udt1 plays a major role in maintaining tapetum development, starting in early meiosis.

This research paper aims to explore some common examples of Seventeenth and Eighteenth century British satire as presented in John Wilmot’s poem “A Satire Against Reason and Mankind” (1679) and Jonathan Swift’s book Gulliver’s Travels (1726/1735) and essay “A Modest Proposal” (1729). It is well known that the political, religious and scientific turmoil of the time had a great impact on the production of this derisive literary genre as there was a general sense of disillusionment with humanity as a species. Yet, contrary to the popular use of satire, two other notable figures, William Shakespeare and John Donne, have used satire for more joyous subject matters. William Shakespeare’s “Sonnet 130” (1609) and “Sonnet 131” (1609) and John Donne’s “The Sun Rising” (1633) all employ satire as a tool of praise instead.

Mini-chromosome maintenance (MCM) 2-9 proteins are related helicases. The first six, MCM2-7, are essential for DNA replication in all eukaryotes. In contrast, MCM8 is not always conserved in eukaryotes but is present in Arabidopsis thaliana. MCM8 is required for 95% of meiotic crossovers (COs) in Drosophila and is essential for meiosis completion in mouse, prompting us to study this gene in Arabidopsis meiosis. Three allelic Atmcm8 mutants showed a limited level of chromosome fragmentation at meiosis. This defect was dependent on programmed meiotic double-strand break (DSB) formation, revealing a role for AtMCM8 in meiotic DSB repair. In contrast, CO formation was not affected, as shown both genetically and cytologically. The Atmcm8 DSB repair defect was greatly amplified in the absence of the DMC1 recombinase or in mutants affected in DMC1 dynamics (sds, asy1). The Atmcm8 fragmentation defect was also amplified in plants heterozygous for a mutation in either recombinase, DMC1 or RAD51. Finally, in the context of absence of homologous chromosomes (i.e. haploid), mutation of AtMCM8 also provoked a low level of chromosome fragmentation. This fragmentation was amplified by the absence of DMC1 showing that both MCM8 and DMC1 can promote repair on the sister chromatid in Arabidopsis haploids. Altogether, this establishes a role for AtMCM8 in meiotic DSB repair, in parallel to DMC1. We propose that MCM8 is involved with RAD51 in a backup pathway that repairs meiotic DSB without giving CO when the major pathway, which relies on DMC1, fails. Citation: Crismani W, Portemer V, Froger N, Chelysheva L, Horlow C, et al. (2013) MCM8 Is Required for a Pathway of Meiotic Double-Strand Break Repair Independent of DMC1 in Arabidopsis thaliana. PLoS Genet 9(1): e1003165.

In plants, male reproductive development is extremely sensitive to adverse climatic environments and (a)biotic stress. Upon exposure to stress, male gametophytic organs often show morphological, structural and metabolic alterations that typically lead to meiotic defects or premature spore abortion and male reproductive sterility. Depending on the type of stress involved (e.g. heat, cold, drought) and the duration of stress exposure, the underlying cellular defect is highly variable and either involves cytoskeletal alterations, tapetal irregularities, altered sugar utilization, aberrations in auxin metabolism, accumulation of reactive oxygen species (ROS; oxidative stress) or the ectopic induction of programmed cell death (PCD). In this review, we present the critically stress-sensitive stages of male sporogenesis (meiosis) and male gametogenesis (microspore development), and discuss the corresponding biological processes involved and the resulting alterations in male reproduction. In addition, this review also provides insights into the molecular and/or hormonal regulation of the environmental stress sensitivity of male reproduction and outlines putative interaction(s) between the different processes involved.

The meiotic developmental pathway in yeast enables both differentiation of vegetative cells into haploid spores that ensure long-term survival, and recombination of the parental DNA to create genetic diversity. Despite the importance of proper metabolic regulation for the supply of building blocks and energy, little is known about the reprogramming of central metabolic pathways in meiotically differentiating cells during passage through successive developmental stages. Metabolic regulation during meiotic differentiation in budding yeast was analysed by integrating information on genome-wide transcriptional activity, 26 enzymatic activities in the central metabolism, the dynamics of 67 metabolites, and a metabolic flux analysis at mid-stage meiosis. Analyses of mutants arresting sporulation at defined stages demonstrated that metabolic reprogramming is tightly controlled by the progression through the developmental pathway. The correlation between transcript levels and enzymatic acti...

Proper regulation of anther differentiation is crucial for producing functional pollen, and defects in or absence of any anther cell type result in male sterility. To deepen understanding of processes required to establish premeiotic cell fate and differentiation of somatic support cell layers a cytological screen of maize male-sterile mutants has been conducted which yielded 42 new mutants including 22 mutants with premeiotic cytological defects (increasing this class fivefold), 7 mutants with postmeiotic defects, and 13 mutants with irregular meiosis. Allelism tests with known and new mutants confirmed new alleles of four premeiotic developmental mutants, including two novel alleles of msca1 and single new alleles of ms32, ms8, and ocl4, and two alleles of the postmeiotic ms45. An allelic pair of newly described mutants was found. Premeiotic mutants are now classified into four categories: anther identity defects, abnormal anther structure, locular wall defects and premature degradation of cell layers, and/or microsporocyte collapse. The range of mutant phenotypic classes is discussed in comparison with developmental genetic investigation of anther development in rice and Arabidopsis to highlight similarities and differences between grasses and eudicots and within the grasses.

MEZ1 (MEiosis-associated Zinc-finger protein 1) was first isolated as an anther-specific cDNA from Petunia hybrida. In the present study, we report its functional characterization, including its spatial and temporal expression profiles and phenotypes in MEZ1-silenced plants. MEZ1 transcripts were specifically localized in pollen mother cells during early stages of anther development, and were later distributed in vegetative tissues in anthers. Silencing of MEZ1 by cosuppression resulted in several anomalies during male meiosis that included inability of chromosomes to condense, loss of meiotic synchrony, and premature and apparently uncontrolled cytokinetic events. Consequently, by the end of meiosis 8–10 cells, instead of the normal 4, with varying DNA contents were formed in the MEZ1-silenced meiocytes. Most of these aborted prematurely, and those that matured had a distinctive morphology. MEZ1-silenced plants were female sterile when pollinated with wild-type pollen but they infrequently produced a few seeds upon self-pollination. Resulting T1 plants had increased ploidy levels and exhibited severe anomalies during male meiosis, rendering them completely sterile. We discuss possible role of MEZ1 in the proper progression of plant meiosis.