Sex Chromosomes In Meiosis Research Articles

Meiotic Behavior of Achiasmate Sex Chromosomes in the African Pygmy Mouse Mus mattheyi Offers New Insights into the Evolution of Sex Chromosome Pairing and Segregation in Mammals.

X and Y chromosomes in mammals are different in size and gene content due to an evolutionary process of differentiation and degeneration of the Y chromosome. Nevertheless, these chromosomes usually share a small region of homology, the pseudoautosomal region (PAR), which allows them to perform a partial synapsis and undergo reciprocal recombination during meiosis, which ensures their segregation. However, in some mammalian species the PAR has been lost, which challenges the pairing and segregation of sex chromosomes in meiosis. The African pygmy mouse Mus mattheyi shows completely differentiated sex chromosomes, representing an uncommon evolutionary situation among mouse species. We have performed a detailed analysis of the location of proteins involved in synaptonemal complex assembly (SYCP3), recombination (RPA, RAD51 and MLH1) and sex chromosome inactivation (γH2AX) in this species. We found that neither synapsis nor chiasmata are found between sex chromosomes and their pairing is notably delayed compared to autosomes. Interestingly, the Y chromosome only incorporates RPA and RAD51 in a reduced fraction of spermatocytes, indicating a particular DNA repair dynamic on this chromosome. The analysis of segregation revealed that sex chromosomes are associated until metaphase-I just by a chromatin contact. Unexpectedly, both sex chromosomes remain labelled with γH2AX during first meiotic division. This chromatin contact is probably enough to maintain sex chromosome association up to anaphase-I and, therefore, could be relevant to ensure their reductional segregation. The results presented suggest that the regulation of both DNA repair and epigenetic modifications in the sex chromosomes can have a great impact on the divergence of sex chromosomes and their proper transmission, widening our understanding on the relationship between meiosis and the evolution of sex chromosomes in mammals.

RNF8 is not required for histone-to-protamine exchange in spermiogenesis†.

While an E3 ubiquitin ligase, RNF8, was initially reported to be required for histone-to-protamine exchange in spermiogenesis, we subsequently demonstrated that RNF8 is not involved in this process. Nevertheless, reflecting a lingering misunderstanding in the field, a growing number of studies have continued to postulate a requirement for RNF8 in the histone-to-protamine exchange. For example, a recent study claimed that a mouse PIWI protein, MIWI, controls RNF8-mediated histone-to-protamine exchange. Here, confirming our earlier conclusions, we show that RNF8 is required neither for the establishment of histone H4K16 acetylation, which is an initial step in histone removal during spermiogenesis, nor for the incorporation of two protamine proteins, PRM1 and PRM2. Thus, whereas RNF8 mediates ubiquitination of H2A on the sex chromosomes in meiosis, during the prior stage of spermatogenesis, our genetic evidence underscores that RNF8 is not involved in histone-to-protamine exchange.

Back to the roots: segregation of univalent sex chromosomes in meiosis.

In males of many taxa, univalent sex chromosomes normally segregate during the first meiotic division, and analysis of sex chromosome segregation was foundational for the chromosome theory of inheritance. Correct segregation of single or multiple univalent sex chromosomes occurs in a cellular environment where every other chromosome is a bivalent that is being partitioned into homologous chromosomes at anaphase I. The mechanics of univalent chromosome segregation vary among animal taxa. In some, univalents establish syntelic attachment of sister kinetochores to the spindle. In others, amphitelic attachment is established. Here, we review how this problem of segregation of unpaired chromosomes is solved in different animal systems. In addition, we give a short outlook of how mechanistic insights into this process could be gained by explicitly studying model organisms, such as Caenorhabditis elegans.

Cytogenetics of the true bug infraorder Cimicomorpha (Hemiptera, Heteroptera): a review.

The Cimicomorpha is one of the largest and highly diversified infraorders of the Heteroptera. This group is also highly diversified cytogenetically and demonstrates a number of unusual cytogenetic characters such as holokinetic chromosomes; m-chromosomes; multiple sex chromosome systems; post-reduction of sex chromosomes in meiosis; variation in the presence/absence of chiasmata in spermatogenesis; different types of achiasmate meiosis. We present here a review of essential cytogenetic characters of the Cimicomorpha and outline the chief objectives and goals of future investigations in the field.

Meiosis in gray voles of the subgenus Microtus (Rodentia, Arvicolinae) and in their hybrids

The results of light and electron microscopic (EM) studies of meiosis in Microtus arvalis males of the karyoform "arvalis" (2n = 46, NFa = 80), in hybrids between the chromosomal forms arvalis and obscurus (2n = 46, NFa = 68), in M. rossiaemeridionalis voles (2n = 54, NFa = 54), and in a hybrid between the species M. rossiaemeridionalis and M. kermanensis (2n = 54, NFa = 54) are presented. SC (synaptonemal complex) karyotypes of the parental forms and the hybrids were constructed on the basis of measurements of the length ofautosomal SCs revealed by the EM analysis in spermatocytes at the stage of middle pachytene. The SC karyotypes of M. arvalis and the hybrids female obscurus x male arvalis consist of 22 synaptonemal complexes of autosomal bivalents and the axial elements of the synaptonemal complexes of the sex chromosomes X and Y. The SC karyotypes of M. rossiaemeridionalis and the hybrid M. rossiaemeridionalis x M. kermanensis consist of 26 synaptonemal complexes of autosomal bivalents and a sex bivalent; they differ only in the length of the Y chromosome axis (Y chromosome in the hybrid was inherited from M. kermanensis). Asynaptic configurations of the autosomal SCs were not observed in the hybrids. The SC axial elements of the X and Y chromosomes in the parental forms and in the hybrids were located close to each other throughout pachytene, but they did not form a synaptic region. The normal synapsis in sterile hybrids (M. rossiaemeridionalis x M. kermanensis) and the behavior of the sex chromosomes in meiosis in fertile and sterile hybrids are discussed in the context of specific features of meiosis and reproductive isolation.

Semidominant Effect of the l(1)ts403 ( sbr 10 ) Mutation on Sex Chromosome Nondsjunction in Meiosis in Drosophila melanogaster Females Exposed to Heat

The sbrgene of Drosophila melanogasterbelongs to the NXF(nuclear export factor) family responsible for the mRNA transport from nucleus to cytoplasm. We have shown that in the heat-exposed (37°C, 1 h) females, the l(1)ts403(sbr10) mutation leads, in particular, to the high-frequency nondisjunction and loss of sex chromosomes in meiosis. For this trait, the incomplete dominance of the sbr10 mutation is observed. At the same time, the sbr10 mutation is recessive for many other traits of the heat-exposed flies: reduced viability, low fertility, impaired synthesis of the heat shock proteins, etc. The females heterozygous for the null allele (Df(1)vL4, a deletion eliminating gene srb) do not differ from females homozygous for the wild-type allele in frequency of the heat shock-induced nondisjunction and loss of sex chromosomes in meiosis. Because of this, the sbr10 mutation can be assigned to the gain-of-function alleles (those gaining the dominance function). Expression of the mutant sbr10 allele against the background of the wild-type allele suggests that in the heat shock-exposed females, the heat-modified product of this ts allele has an active effect on sex chromosome disjunction in meiosis.

Cytogenetical studies on the chromosomes of silk gland cells of the silkworm with special reference to the structure and behavior of the sex chromosomes.

1) The structure of the nuclei in the silk gland cells of the silkworm, Bombyx mori, was investigated with special reference to the fine structure of the sex-heterochromatin body (SB), using both diploids and experimentally induced polyploids.2) Microscopic observations revealed that the SB was not a homogeneous mass, but it was surrounded by a layer of chromatin substances formed by the coiling and folding of fibrils.3) The SB was clearly observed in the silk gland nuclei in acetic orcein squashed preparations, being 100% in the female (SB1) and 0% in the male (SB0) in diploids. In the tetraploids, the female nucleus had two SBs (SB2), and the male nucleus contained no SB (SB0).4) On the observation of the segregation of the number of the SB in triploid offsprings from the backcross of the tetraploid female, it was revealed that the ratio of SB2:SB1:SB0 was 1:4:1. The behavior of sex chromosomes in meiosis of the tetraploid female was considered according to the above results.5) Using triploid offsprings from the strain having a translocated Y chromosome marked with visible genes, it is apparent that the SB is corresponding to a Y chromosome.

Association of the sex chromosomes in meiosis of mouse species.

Association of the sex chromosomes in meiosis of mouse species.

Comparative male meiosis in seven species of cotton rats, genus Sigmodon.

A study of the male meiosis in seven species of cotton rats, genus Sigmodon, was carried out. The general course of meiosis in four species, S. hispidus, S. leucotis, S. ochrognathus, and S. alleni, is similar to that in other mammals studied. In pachynema, the sex bivalent is negatively heteropycnotic and tightly coiled to form the sex vesicle. In diakinesis, the sex bivalent is elongated and stains lightly. All of these species have a diploid number of 52, and 26 bivalents are seen in diakinesis. In the remaining three species, S. arizonae, S. mascotensis, and S. fulviventer, the sex bivalent is negatively heteropycnotic in pachynema with no indication of condensation. It would appear that the functional activity of the sex chromosomes in meiosis in these species is completed before pachynema. Diakinesis stages in S. arizonae (2n=22, 24) possess 11 or 12 bivalents; in S. fulviventer (2n=28, 29, or 30) 14 or 15 bivalents; and S. mascotensis (2n=28) 14 bivalents. Differences found in activity of the sex bivalent can be correlated with the two groups of Sigmodon established on the basis of diploid and fundamental numbers and represent another expression of the differences in genomes between the two groups.

The meiotic chromosomes of man.

Information was obtained on the chromosome number, and the behavior of autosomes as well as of the sex chromosomes in meiosis in human male germ cells derived from 25 Japanese patients, 4 to 79 years in age, who were hospitalized mostly due to epididymitis, prostate cancer, undescended testes or infertility. In 16 out of the 25 specimens, the chromosome numbers, 46 in 2n and 23 in n, were consistently established together with an XY sex-determining mechanism based on spermatogonial and spermatocyte divisions. No reliable counts were obtained from the remaining 9 cases, because of that they provided no cells for precise investigation. The X and Y chromosomes during the leptotene stage were observed as two separate heteropycnotic bodies lying along the inner wall of the nucleus, while at pachytene they formed a sex-vesicle after homologous pairing. At the diplotene, diakinesis and first metaphase the X and the Y appeared as an isopycnotic bivalent showing an end-to-end association, though there were some cells in which they remained as two separate entities free from contact. Evidence was presented that the X and the Y seemed to associate with each other at the distal end of the short arm of each element. One or sometimes two smallest autosomal bivalents tended to show rather precociously a chiasma-terminalization at the first metaphase. The metaphase chromosomes of the second spermatocytes were evident by the haploid number as well as by their widely diverged chromatids with a characteristic spiral configuration. The testicular materials under study contained in most cases polyploid cells with a considerable frequency in spermatogonia as well as in first and second spermatocytes. Giant sperm heads were observed not infrequently, mostly being abnormal in shape. No significant correlation was obtained between the frequency of polyploid cells and the age of patients so far studied.

Studies on the murine chromosomes. V. A study of the chromosomes in Apodemus, especially with reference to the sex chromosomes in meiosis

Journal of MorphologyVolume 88, Issue 1 p. 93-126 Article Studies on the murine chromosomes. V. A study of the chromosomes in Apodemus, especially with reference to the sex chromosomes in meiosis† Sajiro Makino, Sajiro Makino Zoological Institute, Hokkaido University, SapporoSearch for more papers by this author Sajiro Makino, Sajiro Makino Zoological Institute, Hokkaido University, SapporoSearch for more papers by this author First published: January 1951 https://doi.org/10.1002/jmor.1050880105Citations: 16 † Contribution no. 216 from the Zoological Institute, Faculty of Science, Hokkaido University, Sapporo, Japan. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume88, Issue1January 1951Pages 93-126 RelatedInformation