![]() ![]() This spatial anticorrelation of crossovers, first observed more than a century ago ( Muller, 1916 Sturtevant, 1913), has since been characterized and quantified in a wide variety of organisms and appears to be a ubiquitous feature of meiosis.įailure to form the obligate crossover results in chromosome mis-segregation and aneuploidy, and the implications of these events on reproductive health are well documented ( Gruhn et al., 2019 Wang et al., 2017). For instance, the roundworm Caenorhabditis elegans undergoes exactly one crossover per chromosome in wild-type animals, and only sometimes achieves two (well-separated) crossovers in 35 Mb fusion chromosomes ( Hillers and Villeneuve, 2003 Libuda et al., 2013 Yokoo et al., 2012). Crossover interference can be incredibly robust and exert inhibition over whole chromosomes. Here, we focus on an intriguing form of regulation called crossover interference, in which closely spaced crossovers are conspicuously underrepresented, and hence the remaining crossovers are separated by larger intervals than would be expected for independent events ( Koszul et al., 2012). Furthermore, inhibitory mechanisms limit excessive crossovers, resulting in a tight distribution of total crossover number ( Cole et al., 2012 Zickler and Kleckner, 2015). For instance, because crossovers are required for reliable chromosome segregation at meiotic anaphase I, multiple mechanisms assure the presence of at least one ‘obligate’ crossover on each chromosome. While crossovers are formed at random locations in any given meiosis, the number of crossovers is tightly regulated to ensure healthy progeny. (2017), where they were published under a CC BY 4.0 license. As implied by the data shown in C, at larger scales, proteins might also exhibit translational motion within the SC-CR and/or turnover (i.e. At the smallest scale, individual proteins may rearrange locally (‘wiggle’). (D) Schematic illustration of possible liquid-like dynamics within the SC-CR. The axis protein HIM-3 does not significantly redistribute, whereas the SC-CR protein SYP-3 does, indicating the liquid-like nature of the SC-CR. A local pool of fluorescent protein within the nucleus (dashed line) is photoconverted with a spatially defined pulse of UV light (blue lightning bolt). ![]() (C) Dynamics of the axis (HIM-3, top) and the SC-CR (SYP-3, bottom) as detected by photoconversion of mMaple3 fluorescent protein fusions in live C. Bottom: schematic of chromatin (gray), axis (orange) and SC-CR (teal). elegans chromosomes during meiosis, with ladder-like structure of the SC-CR superimposed. Right: a tightly regulated subset of these breaks form crossovers between homologous chromatids, while all other breaks are repaired without forming crossovers. Middle: the homologs are brought into close physical proximity by the SC-CR (teal), and breaks (blue) are induced at random positions. (A) Left: the axis (orange) assembles onto the parental chromosomes (dark and light gray pairs of sister chromatids). The chromosomal environment during crossover formation. ![]()
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