Micrococcal nuclease sequencing of pig sperm suggests a relationship between nucleosome retention and both semen quality and early embryo development

Resumen del póster presentado a la 38th International Conference on Animal Genetics (ISAG), celebrada virtualmente del 26 al 30 de julio de 2021.
In animals, the chromatin structure of the mature spermatozoon is ultra-compacted due to the replacement of histones by protamines during spermatogenesis. However, a small fraction of nucleosomes remains bound to DNA at specific sites of the genome and it has been linked to sperm biology and embryogenesis. The genomic characterization of nucleosome occupancy in the sperm chromatin could help identifying molecular markers for sperm quality and fertility traits. Nonetheless, these maps are not yet available for most livestock species, including swine. In this study, we performed micrococcal nuclease digestion followed by high-throughput sequencing on pig ejaculated spermatozoa and mapped the mono-nucleosomal and sub-nucleosomal chromatin fractions. We found 25,293 mono-nucleosomal and 4,239 sub-nucleosomal peaks covering 0.3% and 0.02% of the porcine genome, respectively. We detected positional conservation of the nucleosome-associated DNAs in sperm between human and pig. We also carried gene ontology analysis of the genes mapping nearby the mono-nucleosomal peaks and also searched for putative transcription factor binding motifs within the mono-nucleosomal peaks and found an enrichment for sperm function and embryo development-related processes. Remarkably, we detected enrichment for the canonical binding site of Znf263. In humans, this transcription factor has been suggested as a key regulator of the genes with paternal preferential expression during early embryo development. In addition, we also observed co-occupancy of the RNAs present in pig sperm and these RNAs related to sperm quality, with the mono-nucleosomal peaks. We also found a co-location trend between GWAS hits for semen quality in swine and the mono-nucleosomal sites. The results obtained in this study clearly indicate that there is a relationship between nucleosome positioning in sperm with sperm phenotypes and embryo development.