Abstract
During sexual reproduction the parental homologous chromosomes find each other (pair) and align along their lengths by integrating local sequence homology with large-scale contiguity, thereby allowing for precise exchange of genetic information. The Synaptonemal Complex (SC) is a conserved zipper-like structure that assembles between the homologous chromosomes, bringing them together and regulating exchanges between them. However, the molecular mechanisms by which the SC carries out these functions remain poorly understood. Here we isolated and characterized two mutations in the dimerization interface in the middle of the SC zipper in C. elegans. The mutations perturb both chromosome alignment and the regulation of genetic exchanges. Underlying the chromosome-scale phenotypes are distinct alterations to the way SC subunits interact with one another. We propose a model whereby the SC brings homologous chromosomes together through two activities: obligate zipping that prevents assembly on unpaired chromosomes; and a tendency to extend pairing interactions along the entire length of the chromosomes.
Highlights
In meiotic cells, homologs are regulated precisely and synchronously as a pair via direct physical interaction, enabling them to exchange genetic information
Our analysis indicates that while the chromosomal phenotypes of our Nterminal syp-1 mutations are related, they stem from different effects on the biophysical properties of the Synaptonemal Complex (SC). syp-1K42E weakens intra-SC interactions as reflected by poor assembly into polycomplexes, increased 1,6-hexanediol sensitivity, and inefficient recruitment onto chromosomes, all of which are exacerbated by increasing temperature
To ensure that crossover interference is reduced in syp-1K42E (20 ̊C) worms, we identified the location of all crossovers genetically, by crossing syp-1K42E worms that differ in thousands of SNPs and sequencing the genomes of their progeny (Figs 6A and 6B and S5)
Summary
Homologs are regulated precisely and synchronously as a pair via direct physical interaction, enabling them to exchange genetic information. For these interactions to occur, meiotic chromosomes undergo large scale conformational changes. Each homolog becomes elongated and assembles onto a stiff proteinaceous structure called the axis. Homologs pair and align from end to end. Homologs exchange genetic information through generation of crossovers. Crossovers provide the physical linkages that hold the homologs together and allow them to segregate correctly into the gametes. Failure to bring the homologs together, and the subsequent absence of crossovers, result in aneuploid gametes and sterility
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