Genetics of mammalian meiosis
C. Yan Cheng in 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
Velo-cario-Facial Syndrome
Merlin G. Butler, F. John Meaney in Genetics of Developmental Disabilities, 2019
The loss of DNA that causes VCFS is an interstitial deletion from the long arm of chromosome 22 that resides within a region of the genome that is highly susceptible to mutation. This region of chromosome 22 seems to be one of the most mutable regions in the entire human genome, thus accounting for the high rate of spontaneous mutation and the large number of nonfamilial cases. The mechanism for the deletion has been determined to occur during gametogenesis (34). The rearrangement happens as a result of a recombinant event in the first meiotic prophase (Prophase I) during synapsis. There is an unusual arrangement of chromosome 22 in the region that marks the normal breakpoint for the proximal end of the deletion and the region at the distal end. In both of these regions, there occurs a series of low copy repeats (LCRs) of DNA that are largely homologous (Fig. 4).
The Immunoglobulin Variable-Region Gene Repertoire and Its Analysis
Cliburn Chan, Michael G. Hudgens, Shein-Chung Chow in Quantitative Methods for HIV/AIDS Research, 2017
In addition to combinatorial diversity, IgVRG exhibits junctional diversity. The enzymatic complex consisting of the recombination activating genes RAG1 and RAG2 binds to a recombination signal (RS) adjacent to each of the V, D, and J genes, bringing the genes into close proximity. Proper ordering of the genes is enforced by the so-called 12/23 rule. There are two different types of RS, one with a 12-nucleotide spacer and one with a 23-base spacer. Synapsis occurs only between heterogeneous pairs. The recombinase nicks the DNA at the start of each RS, resulting in a DNA hairpin on each gene, which is then cleaved stochastically by the Artemis complex, resulting in variable recombination points. Because of the hairpin structure, this cleavage may occur beyond the end of the coding region into the noncoding strand, resulting in the appearance of p-nucleotides (p for palindromic). Terminal deoxynucleotidyl transferase may then add several n-nucleotides (n for nontemplated), which are yet another source of stochasticity. The strands then pair in complementary regions, and unpaired nucleotides are removed and filled in to form the final junction region [19,25,26]. The site of RAG-mediated cleavage and n-nucleotides together supply the junctional diversity of the antibody repertoire.
Zoledronic acid induces cytogenetic toxicity in male germline cells of Swiss albino mice
Published in Drug and Chemical Toxicology, 2019
Ramakrishna Dasari, Sunil Misra
Aberrant chromosomal segregation is a consequence of errors in the series of programed and sequential events occurring at prophase-I of meiosis defined by a number of characteristic morphological changes associated with the pairing of homologous chromosomes, synapsis, asynapsis, and recombination (Garcia-Muse and Boulton 2007). For analyzing the cytogenetic toxicity of ZA, three different concentrations (2, 4, and 8 mg/kg b.wt.) were exposed to mice. The group of positive control mice that received CP induced significantly higher percentage of CAs in the spermatogonial cells which are in agreement with the earlier reports (Rathenberg 1975, Choudhury et al. 2002). Further, CP induced a significantly higher percentage of aberrant primary spermatocytes with atypical bivalents at week 4 posttreatment and also significantly higher percentage of abnormal sperms at week 8 posttreatment justifying its clastogenic potential in germline cells.
Long-term exposure to formaldehyde induced down-regulation of SPO11 in rats
Published in Inhalation Toxicology, 2021
Pan Ge, Xiang Zhang, Yan-qi Yang, Mo-qi Lv, Dang-xia Zhou
Spermatogenesis involves highly complex physiological processes, especially meiosis (Griswold 2016). When adverse environmental factors interfere or genetic materials are disturbed, the normal spermatogenic process, particularly meiosis, may be affected, leading to the development of spermatogenic disorders. Meiosis is an essential part of spermatogenesis, and the SPO11 gene is one of the important genes involved in meiosis. SPO11, a meiosis-related gene, is a type II topoisomerase, which mediates DNA DSBs to trigger chromosomal breaks in meiotic recombination and promote pairing with synaptonemal complex formation between homologous chromosomes (Bloomfield 2016). Smirnova et al. reported that SPO11-/-mice could not complete chromosome synapsis and chromosome condensation, resulting in abnormal spermatogenesis (Smirnova et al. 2006). Moreover, the study of Ren et al. showed that the SPO11 gene C631T polymorphism might be a susceptible genetic factor leading to male infertility (Ren et al. 2017).
Homocysteine can aggravate depressive like behaviors in a middle cerebral artery occlusion/reperfusion rat model: a possible role for NMDARs-mediated synaptic alterations
Published in Nutritional Neuroscience, 2023
Mengying Wang, Xiaoshan Liang, Qiang Zhang, Suhui Luo, Huan Liu, Xuan Wang, Na Sai, Xumei Zhang
To observe whether HCY treatment could induce synaptic structural changes in the rat hippocampal region after MCAO, the number of synapses and the area of postsynaptic density were detected by TEM (Figure 3). In the SHAM group, the membranes of synapses were clear and had complete outlines, and abundant postsynaptic density was detected. Compared with the SHAM group, ultrastructure of synapsis in the MCAO group exhibited vague membranes, decreased quantity of synapse (P < 0.05, Figure 3(a)), and thinner postsynaptic densities (P = 0.004, Figure 3(b)). The administration of HCY further damaged the related synaptic morphology, including decreased number of synapses and downregulated postsynaptic density thickness, compared to the MCAO group (P = 0.019). These results suggested that HCY might cause synaptic loss and pathological changes in the hippocampus following ischemic injury.
Related Knowledge Centers
- Chromosomal Crossover
- Cytoskeleton
- Sex Chromosome
- Synaptonemal Complex
- Autosome
- Meiosis
- Mitosis
- Genetic Recombination
- Chiasma
- Metaphase