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Genetics of mammalian meiosis
Published in C. Yan Cheng, Spermatogenesis, 2018
During the extended prophase of meiosis I, homologous chromosomes are physically juxtaposed in a process called synapsis. The synaptonemal complex (SC) provides the physical connection between homologous chromosomes during synapsis.21,22 The synaptonemal complex is a 200-nm-wide tripartite protein structure consisting of two lateral elements (LEs) and one central element (CE). One LE is formed along the sister chromatids. Transverse elements (TFs) connect the lateral elements and the central element. Under transmission electron microscopy, the tripartite structure of SC is shown by the two electron-dense LEs and one electron-dense CE in between.23 The LEs and CE of the SC cannot be resolved as individual structures under conventional light microscopy. Superresolution imaging has not only revealed the tripartite structure but also the organization of SC as a twisted helical structure.24 Immunoelectron microscopy and superresolution imaging further demonstrate that the CE is a bilayered helical structure.24,25
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
prophase) when a complex process (mediated by the synaptonemal complex) allows homologous parts of two non-sister chromatids to change places. The DNA from two parents can, by this means, be combined on a single chromosome. See also: evolution; natural selection; reproduction
Sex Chromosome Pairing and Fertility in the Heterogametic Sex of Mammals and Birds
Published in Christopher B. Gillies, Fertility and Chromosome Pairing: Recent Studies in Plants and Animals, 2020
Following the discovery of the synaptonemal complex (SC) by Moses,8 and the realization that the SC represents the fine structure of synapsis, a new approach to the problem of sex-chromosome association in male mammalian meiosis was developed9–11 (reviewed by Solari7 and by Moses12). The enigmatic structure called “sex vesicle”, Lenhossek’s body, or other names,7 was first identified in electron micrographs of mouse spermatocytes as an XY pair.9 This work definitively showed that the “sex vesicle” had no surrounding membranes, and that it had a structure formed by typically packed chromatin fibers and “axes” that were related to the lateral components of SCs.9 Thus, it was possible to analyze the pairing of sex chromosomes by the study of their fine structure.9 This analysis required information on the full structure of the chromosomes, and thus serial thin-sectioning and three-dimensional reconstruction techniques were applied to the reconstruction of the XY pair.13 The first results of these reconstructions showed the existence of an SC in the XY pair of the mouse.11,13 Working with single (thin and thick) sections, Ford and Woollam14 confirmed Solari’s observations on the mouse and showed that an SC could be seen in the XY body of the golden hamster (however, see the exceptionality of the hamster group in Section V). Results of three-dimensional reconstructions accumulated between 1966 and 1971 (reviewed by Solari7 and by Westergaard and von Wettstein15), proved beyond reasonable doubt that partial synapsis was the regular behavior of the X and Y chromosomes in the most-studied eutherian mammals, including man.7 The assumption of Koller and Darlington about “pairing” and “differential” segments in the mammalian XY pair, was finally validated by the discovery of the regular formation of SCs between the X and Y axes at pachytene,7 thus demonstrating the validity of the ultrastructural approach to cytogenetics.
The effects and molecular mechanism of heat stress on spermatogenesis and the mitigation measures
Published in Systems Biology in Reproductive Medicine, 2022
Yuanyuan Gao, Chen Wang, Kaixian Wang, Chaofan He, Ke Hu, Meng Liang
Although the testicular internal thermal stress response can relieve the injury caused by apoptosis, there are still some damaged spermatocytes from thermal stimulation caused by apoptosis; at this point, the sperm is not much different from normal sperm, but they have a lower activity, mainly because the sperm DNA integrity is affected by heat-induced DNA damage (Lewis et al. 2013). In fact, heat stress can cause disturbances in the synaptonemal complex of early spermatocytes. Excessive heat not only prevents the synaptonemal complex from functioning properly, forming fewer and fewer distal crosses, but also results in DNA fragmentation, leading to the existence of unpaired Y chromosomes and apoptosis of spermatocytes (Houston et al. 2018). In addition to damaging DNA integrity, heat stress also leads to reduced DNA synthesis and the degradation of mRNAs and proteins related to cell survival.
Genetic variations as molecular diagnostic factors for idiopathic male infertility: current knowledge and future perspectives
Published in Expert Review of Molecular Diagnostics, 2021
Mohammad Karimian, Leila Parvaresh, Mohaddeseh Behjati
The synaptonemal complex is an important component for chromosome pairing, segregation, and recombination. Hormad1 is essential for mammalian gametogenesis because male knockout mice are infertile. Hormad1-deficient testes in the early stages of pachytene show meiosis arrest without demonstration of synaptonemal complexes [152]. To analyze the hypothesis that human HORMAD1 gene defect is associated with human azoospermia induced by meiosis arrest, mutation analysis in all coding regions was performed by Miyamoto et al. By sequence analysis, SNP1 (163A> G), SNP2 (501T>G) and SNP3 (918C>T) were found in exons 3, 8, and 10. Both SNP1 and SNP2 were associated with human azoospermia resulting from the complete arrest of primary meiosis. They suggested that HORMAD1 has an essential mitotic function in human spermatogenesis [153].
Differentiation of spermatogonial stem cells by soft agar three-dimensional culture system
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Elham Mohammadzadeh, Tooba Mirzapour, Mohammad Reza Nowroozi, Hamid Nazarian, Abbas Piryaei, Fatemeh Alipour, Sayed Mostafa Modarres Mousavi, Marefat Ghaffari Novin
In this study, the expression rate of the meiotic gene of Scp3, as a marker of synaptonemal complex formation in the meiosis process, was investigated in three groups. The results showed that on day 7 after culture, the highest expression of this gene was observed in the SACS group, which is significantly higher than the gelatin group (p < .01), but there was no significant difference between the SACS and control groups as well as the gelatin and control groups on day 7 after culture. Also, on the 14th day after culture, the expression of this marker was significantly higher in the SACS group rather than gelatin group (p < .05). The mean expression of Scp3 gene on day 14 in the SACS group was 3.26 ± 0.16 and in gelatin group was 0.94 ± 0.01 (Figure 6).