PT  - JOURNAL ARTICLE
AU  - Carolina Galan
AU  - Ryan W. Serra
AU  - Fengyun Sun
AU  - Vera D. Rinaldi
AU  - Colin C. Conine
AU  - Oliver J. Rando
TI  - Cytosine methylation dynamics during post-testicular sperm maturation in mammals
AID  - 10.1101/2020.02.14.949487
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 2020.02.14.949487
4099  - http://biorxiv.org/content/early/2020/02/14/2020.02.14.949487.short
4100  - http://biorxiv.org/content/early/2020/02/14/2020.02.14.949487.full
AB  - Beyond the haploid genome, mammalian sperm contribute a payload of epigenetic information which can modulate offspring phenotypes. Recent studies have shown that the small RNA payload of sperm undergoes extensive remodeling during post-testicular maturation in the epididymis. Intriguingly, epididymal maturation has also been linked to changes in the sperm methylome, suggesting that the epididymis might play a broader role in remodeling the sperm epigenome. Here, we build on prior studies of the maturing sperm methylation landscape, further characterizing the genome-wide methylation landscape in seven germ cell populations collected from throughout the male reproductive tract. Overall, we find very few changes in the cytosine methylation landscape between testicular germ cell populations and cauda epididymal sperm, demonstrating that the sperm methylome is largely stable throughout post-testicular maturation. Intriguingly, although our sequencing data suggested that caput epididymal sperm exhibit a highly unusual methylome, follow-up studies revealed that this resulted from contamination of caput sperm by extracellular DNA. Extracellular DNA formed web-like structures that ensnared sperm, was present only in the caput epididymis of virgin males, where it was associated with citrullinated histone H3 and presumably resulted from a PAD-driven genome decondensation process. Taken together, our data emphasize the stability of the cytosine methylation landscape in mammalian sperm, and identify a surprising but transient period during which immature sperm are associated with extracellular DNA.