Chromatin and extracellular vesicle associated sperm RNAs

Abstract

A diverse pool of RNAs remain encapsulated within the transcriptionally silent spermatozoon despite the dramatic reduction in cellular and nuclear volume following cytoplasm/nucleoplasm expulsion. The impact of this pronounced restructuring on the distribution of transcripts inside the sperm essentially remains unknown. To define their compartmentalization, total RNA >100 nt was extracted from sonicated (SS) mouse spermatozoa and detergent demembranated sucrose gradient fractionated (Cs/Tx) sperm heads. Sperm RNAs predominately localized toward the periphery. The corresponding distribution of transcripts and thus localization and complexity 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 embryo. In comparison, transcripts enriched in sonicated sperm contributed to the mitochondria and exosomes along with several nuclear transcripts including the metastasis associated lung adenocarcinoma transcript 1 (Malat1) and several small nucleolar RNAs. Their preferential peripheral localization suggests that chromatin remodeling during spermiogenesis is not limited to nucleoproteins as part of the nucleoprotein exchange.

Adolescence and the next generation

“…Sperm maturation takes between 70 and 100 days in humans, predominantly in the seminiferous tubules that are in constant contact with supporting Sertoli cells. This is followed by a 1-2 week transitional period in the epididymis, during which time proteins and a small amount of RNA are selectively shuttled into the developing sperm 51,52 . The paternal preconception environment modulates the RNA content of the developing sperm, with possible effects on post-fertilization development and offspring phenotypes 53 .…”

Segment-specific regulation of epididymal gene expression

“…Moreover, Nixon et al (2015a,b) showed that also the miRNA profile of mouse spermatozoa changes during epididymal transit from caput to cauda, and in a study by Johnson et al (2015), long (>100 nt) RNA content of spermatozoa was shown to comprise extracellular-vesicle-associated RNA, possibly incorporated into spermatozoa during epididymal transit.…”

Glycosylation of extracellular vesicles: current knowledge, tools and clinical perspectives

“…These examples of potent bioactivity and the biocompatible nature of EVs have inspired the development of vesicles as vehicles for both drug and gene therapy delivery for a large number of applications [23]. EVs may even play a direct role in evolution as studies show EV-mediated transfer of nucleic acids into sperm cells [24]. Final evidence for the importance of EVs is given by their existence across taxonomic kingdoms, from archaea through bacteria to plants and animals [1].…”