Recent progress in elucidating the function of synaptonemal complex (SC) proteins and of cohesins in meiocytes made possible, in particular, through the analysis of mice deficient in SC or cohesin proteins has significantly enriched our understanding of how meiotic chromosome architecture is determined. Cohesins and the SC proteins act together in generating the characteristic axis-loop structure of meiotic chromosomes, their pairing into bivalents, their ability to recombine, and to be properly segregated. This minireview attempts to summarize the current knowledge with a focus on higher eukaryotic systems and to ask questions that ought to be addressed in the future.
"Mitotic prophase chromosome organization may turn out to be the same as that of meiotic prophase chromosomes (Kleckner et al. 2012). Molecular studies of pachytene chromosomes have identified several types of axis components: mitotic structural proteins like topoisomerase II, condensins, cohesins, and cohesin-associated proteins, including meiosisspecific versions of some of these proteins; meiosis-specific axis components; and structural components of the SC, which are also unique to meiosis (Moens and Earnshaw 1989; Page and Hawley 2004; Revenkova and Jessberger 2006; Wojtasz et al. 2009; Wood et al. 2010, and references therein; Liu and Colaiácovo 2013). In many organisms (including budding and fission yeast, mammals, Arabidopsis, rice, Drosophila, and C. elegans), prominent meiotic axis components include one or more HORMA-domain proteins. "
"It is worthwhile to consider several details of SC protein diversity. Lateral elements (LEs) of the SC are formed on the basis of chromosomal axial elements, which connect sister chromatids and consist mostly of cohesins . The LEs are joined together to produce the integral SC structure via a zipper of transversal filaments, which pass through the SC central space. "
[Show abstract][Hide abstract] ABSTRACT: The problems of the origin and evolution of meiosis include the enigmatic variability of the synaptonemal complexes (SCs) which, being morphology similar, consist of different proteins in different eukaryotic phyla. Using bioinformatics methods, we monitored all available eukaryotic proteomes to find proteins similar to known SC proteins of model organisms. We found proteins similar to SC lateral element (LE) proteins and possessing the HORMA domain in the majority of the eukaryotic taxa and assume them the most ancient among all SC proteins. Vertebrate LE proteins SYCP2, SYCP3, and SC65 proved to have related proteins in many invertebrate taxa. Proteins of SC central space are most evolutionarily variable. It means that different protein-protein interactions can exist to connect LEs. Proteins similar to the known SC proteins were not found in Euglenophyta, Chrysophyta, Charophyta, Xanthophyta, Dinoflagellata, and primitive Coelomata. We conclude that different proteins whose common feature is the presence of domains with a certain conformation are involved in the formation of the SC in different eukaryotic phyla. This permits a targeted search for orthologs of the SC proteins using phylogenetic trees. Here we consider example of phylogenetic trees for protozoans, fungi, algae, mosses, and flowering plants.
"The cohesin subunit SMC3 is known to co-localize with the synaptonemal complex proteins SYCP2 ⁄ - SYCP3 during the pachytene stage of meiosis in the mouse (Eijpe et al. 2000; Prieto et al. 2004; Revenkova and Jessberger 2006). Importantly, we have recently demonstrated that SMC3 decorates the axial elements of the synaptonemal complex during meiotic chromosome synapsis in horse spermatocytes, therefore providing a "
[Show abstract][Hide abstract] ABSTRACT: The cellular effects of tall fescue grass-associated toxic ergot alkaloids on stallion sperm and colt testicular tissue were evaluated. This was a continuation of an initial experiment where the effects of toxic ergot alkaloids on the stallion spermiogram were investigated. The only spermiogram parameter in exposed stallions that was affected by the toxic ergot alkaloids was a decreased gel-free volume of the ejaculate. This study examined the effect of toxic ergot alkaloids on chilling and freezing of the stallion sperm cells. The effect of toxic ergot alkaloids on chilled extended sperm cells for 48 h at 5°C was to make the sperm cells less likely to undergo a calcium ionophore-induced acrosome reaction. The toxic ergot alkaloids had no effect on the freezability of sperm cells. However, if yearling colts were fed toxic ergot alkaloids, then the cytological analysis of meiotic chromosome synapsis revealed a significant increase in the proportion of pachytene spermatocytes showing unpaired sex chromosomes compared to control spermatocytes. There was little effect of ergot alkaloids on adult stallions, but there might be a significant effect on yearling colts.
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