Prendergast, R. | Search bioRxiv

bioRxiv2023

Distinct and interdependent functions of three RING proteins regulate recombination during mammalian meiosis

During meiosis, each pair of homologous chromosomes becomes connected by at least one crossover, as required for accurate segregation at the first division, and adjacent crossovers are widely separated thereby limiting total numbers. In coarsening models, crossover patterning results from nascent recombination sites competing to accrue a limiting pro-crossover RING-domain protein (COR) that diffuses between synapsed chromosomes. Here we delineate the localization dynamics of three mammalian CORs in mouse and determine their interdependencies. RNF212, HEI10 and a new member RNF212B show divergent spatiotemporal dynamics along synapsed chromosomes, including profound differences in spermatocytes and oocytes, that are not easily reconciled by elementary coarsening models. Contrasting mutant phenotypes and genetic requirements indicate that RNF212B, RNF212, and HEI10 play distinct but interdependent functions in regulating meiotic recombination and coordinating the events of meiotic prophase-I by integrating signals from DNA breaks, homolog synapsis, the cell-cycle, and incipient crossover sites. SIGNIFICANCEMeiosis produces haploid gametes by precisely halving the chromosome complement. Crossing over between homologous chromosomes (homologs) is essential for their accurate segregation and defects are associated with infertility, miscarriage, and congenital disease. Factors that ensure crossing over between each pair of homologs include mammalian RING-domain proteins RNF212, HEI10, and RNF212B, alleles of which are linked to infertility and heritable variation in crossover rate. This study focuses on understanding the functions and relationships between pro-crossover RING proteins (CORs) in mouse, providing important insights into their roles in regulating recombination, the DNA repair process that gives rise to crossovers. Notably, chromosomal localization dynamics of the three CORs are distinct and show striking sexual dimorphism with important implications for models of crossover control.

genetics↗

bioRxiv2022

The salmon louse genome may be much larger than sequencing suggests

The genome size of organisms impacts their evolution and biology and is often assumed to be characteristic of a species. Here we present the first published estimates of genome size of the ecologically and economically important ectoparasite, Lepeophtheirus salmonis (Copepoda, Caligidae). Four independent L. salmonis genome assemblies of the North Atlantic subspecies Lepeophtheirus salmonis salmonis, including two chromosome level assemblies, yield assemblies ranging from 665 - 790 Mbps. These genome assemblies are congruent in their findings, and appear very complete with Benchmarking Universal Single-Copy Orthologs analyses finding >92% of expected genes and transcriptome datasets routinely mapping >90% of reads. However, two cytometric techniques, flow cytometry and Feulgen image analysis densitometry, yield measurements of 1.3-1.6 Gb in the haploid genome. Interestingly, earlier cytometric measurements reported genome sizes of 939 and 567 Mbps in L. salmonis salmonis samples from Bay of Fundy and Norway, respectively. Available data thus suggest that the genome sizes of salmon lice are variable. Current understanding of eukaryotic genome dynamics suggests that the most likely explanation for such variability involves repetitive DNA, which for L. salmonis makes up {approx}60% of the genome assemblies.

genetics↗