Chromatin and extracellular vesicle associated sperm RNAs

Abstract

A diverse pool of RNAs remain encapsulated withinthe transcriptionally silent spermatozoon despite thedramatic reduction in cellular and nuclear volume followingcytoplasm/nucleoplasm expulsion. The impactof this pronounced restructuring on the distributionof transcripts inside the sperm essentiallyremains unknown. To define their compartmentalization, total RNA >100 nt was extracted from sonicated(SS) mouse spermatozoa and detergent demembranatedsucrose gradient fractionated (Cs/Tx) sperm heads. Sperm RNAs predominately localizedtoward the periphery. The corresponding distributionof transcripts and thus localization and complexitywere then inferred by RNA-seq. Interestingly, the number of annotated RNAs in the CsTx spermheads exhibiting reduced peripheral enrichment wasrestricted. However this included Cabyr, the calciumbindingtyrosine phosphorylation-regulated proteinencoded transcript. It is present in murine zygotesprior to the maternal to the zygotic transition yetabsent in oocytes, consistent with the delivery of internally positioned sperm-borne RNAs to the embryo.In comparison, transcripts enriched in sonicatedsperm contributed to the mitochondria andexosomes along with several nuclear transcripts includingthe metastasis associated lung adenocarcinomatranscript 1 (Malat1) and several small nucleolarRNAs. Their preferential peripheral localizationsuggests that chromatin remodeling during spermiogenesisis not limited to nucleoproteins as part of the nucleoprotein exchange.