The relation of meiosis and mitosis
C. H. Waddington in An Introduction to Modern Genetics, 1950
Fig. 54. Th e Relation of M itosis and Meiosis (according to Darlington).βThe stages of mitosis are shown on the left, and the corresponding stages of meiosis on the right. Note that the chromosomes are double at their first appearance in mitosis, but not in the earliest (leptotene) stage of meiotic prophase. They pair in zygotene, beginning to become double (split) in pachytene, and are double in the last stages of meiotic prophase (diplotene and diakinesis). In mitosis anaphase begins by the division of the centromeres, but in meiosis this does not occur till the anaphase of the second division (not shown).
Genetics of mammalian meiosis
C. Yan Cheng in Spermatogenesis, 2018
This chapter aims to provide an overview of mammalian meiosis with a focus on the major advances. The timing of meiotic initiation differs between sexes. In males, spermatogonia enter meiosis at puberty, whereas in females, oogonia enter meiosis shortly after sex determination at the embryonic stage. During the meiotic prophase I, chromosomes undergo rapid movement. Loss of any of the proteins causes failures in chromosome movement, homolog pairing, and chromosomal synapsis, demonstrating the requirement of telomere-led bouquet formation for meiosis. In many species including mouse, chromosomal synapsis and meiotic recombination are interdependent. The synaptonemal complex provides a structural framework for meiotic recombination. Meiotic recombination initiates and stabilizes chromosomal synapsis. In mouse meiotic germ cells, a subset of double-strand breaks (DSBs) are turned into ~25 crossovers per cell and the remaining DSBs result in noncrossovers. Optimization of the existing in vitro meiosis systems and development of new in vitro systems will likely revolutionize treatment of human infertility.
Androgen regulation of spermatogenesis
C. Yan Cheng in Spermatogenesis, 2018
Spermatogenesis and male fertility is dependent on testosterone signaling. In the testis, testosterone acts via the androgen receptor (AR) in Sertoli, Leydig, peritubular myoid, and other somatic cells to support spermatogenesis. The effects of testosterone and other androgens are mediated by AR, a 110 kDa protein member of the steroid hormone receptor family encoded by a single gene on the X chromosome. Both the nonclassical and classical signaling pathways are required to maintain spermatogenesis. Peritubular cell-specific AR knockout mice display a progressive decrease in spermatogonia and marked reductions in spermatocytes and spermatids that cause the mice to become azoospermic. Testosterone is required for processes that are essential for completing spermatogenesis including maintenance of the blood-testis barrier, transit through meiosis, adhesion of haploid spermatids, and the release of mature sperm. There is some controversy regarding whether testosterone regulates the migration and number of gonocyte germ cells in the fetal testis.
ATP analog-sensitive Pat1 protein kinase for synchronous fission yeast meiosis at physiological temperature
Published in Cell Cycle, 2012
Lubos Cipak, Randy W. Hyppa, Gerald R. Smith, Juraj Gregan
To study meiosis, synchronous cultures are often indispensable, especially for physical analyses of DNA and proteins. A temperature-sensitive allele of the Pat1 protein kinase (pat1-114) has been widely used to induce synchronous meiosis in the fission yeast Schizosaccharomyces pombe, but pat1-114-induced meiosis differs from wild-type meiosis, and some of these abnormalities might be due to higher temperature needed to inactivate the Pat1 kinase. Here, we report an ATP analog-sensitive allele of Pat1 [Pat1(L95A), designated pat1-as2] that can be used to generate synchronous meiotic cultures at physiological temperature. In pat1-as2 meiosis, chromosomes segregate with higher fidelity, and spore viability is higher than in pat1-114 meiosis, although recombination is lower by a factor of 2β3 in these mutants than in starvation-induced pat1+ meiosis. Addition of the mat-Pc gene improved chromosome segregation and spore viability to nearly the level of starvation-induced meiosis. We conclude that pat1-as2 mat-Pc cells offer synchronous meiosis with most tested properties similar to those of wild-type meiosis.
High-throughput knockout screen in
Published in Cell Cycle, 2010
Cornelia Rumpf, Lubos Cipak, Maria Novatchkova, Zhang Li, Silvia Polakova, Andrej Dudas, Ines Kovacikova, Eva Miadokova, Gustav Ammerer, Juraj Gregan
Meiosis is the process which produces haploid gametes from diploid precursor cells. This reduction of chromosome number is achieved by two successive divisions. Whereas homologs segregate during meiosis I, sister chromatids segregate during meiosis II. To identify novel proteins required for proper segregation of chromosomes during meiosis, we applied a high-throughput knockout technique to delete 87 S. pombe genes whose expression is upregulated during meiosis and analyzed the mutant phenotypes. Using this approach, we identified a new protein, Dil1, which is required to prevent meiosis I homolog non-disjunction. We show that Dil1 acts in the dynein pathway to promote oscillatory nuclear movement during meiosis.
Sgo1 is required for co-segregation of sister chromatids during achiasmate meiosis I
Published in Cell Cycle, 2011
Andrej Dudas, Shazia Ahmad, Juraj Gregan
The reduction of chromosome number during meiosis is achieved by two successive rounds of chromosome segregation, called meiosis I and meiosis II. While meiosis II is similar to mitosis in that sister kinetochores are bi-oriented and segregate to opposite poles, recombined homologous chromosomes segregate during the first meiotic division. Formation of chiasmata, mono-orientation of sister kinetochores and protection of centromeric cohesion are three major features of meiosis I chromosomes which ensure the reductional nature of chromosome segregation. Here we show that sister chromatids frequently segregate to opposite poles during meiosis I in fission yeast cells that lack both chiasmata and the protector of centromeric cohesion Sgo1. Our data are consistent with the notion that sister kinetochores are frequently bi-oriented in the absence of chiasmata and that Sgo1 prevents equational segregation of sister chromatids during achiasmate meiosis I.