doi: 10.1093/nar/gkv591 Chromatin and extracellular vesicle associated sperm

A diverse pool of RNAs remain encapsulated within the transcriptionally silent spermatozoon despite the dramatic reduction in cellular and nuclear volume fol-lowing cytoplasm/nucleoplasm expulsion. The im-pact of this pronounced restructuring on the dis-tribution of transcripts inside the sperm essentially remains unknown. To define their compartmental-ization, total RNA>100 nt was extracted from son-icated (SS) mouse spermatozoa and detergent de-membranated sucrose gradient fractionated (Cs/Tx) sperm heads. Sperm RNAs predominately localized toward the periphery. The corresponding distribu-tion of transcripts and thus localization and com-plexity were then inferred by RNA-seq. Interestingly, the number of annotated RNAs in the CsTx sperm heads exhibiting reduced peripheral enrichment was restricted. However this included Cabyr, the calcium-binding tyrosine phosphorylation-regulated protein encoded transcript. It is present in murine zygotes prior to the maternal to the zygotic transition yet absent in oocytes, consistent with the delivery of internally positioned sperm-borne RNAs to the em-bryo. In comparison, transcripts enriched in soni-cated sperm contributed to the mitochondria and exosomes along with several nuclear transcripts in-cluding the metastasis associated lung adenocarci-noma transcript 1 (Malat1) and several small nucle-olar RNAs. Their preferential peripheral localization suggests that chromatin remodeling during spermio-genesis is not limited to nucleoproteins as part of the nucleoprotein exchange