UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology; Graduate School of Biomedical Sciences

Publication Date


Document Type



Developmental Biology | Genetics and Genomics | Reproductive and Urinary Physiology


Beyond the haploid genome, mammalian sperm carry a payload of epigenetic information with the potential to modulate offspring phenotypes. Recent studies show that the small RNA repertoire of sperm is remodeled during post-testicular maturation in the epididymis. Epididymal maturation has also been linked to changes in the sperm methylome, suggesting that the epididymis might play a broader role in shaping the sperm epigenome. Here, we characterize the genome-wide methylation landscape in seven germ cell populations from throughout the male reproductive tract. 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 stable throughout post-testicular maturation. 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, and was present only in sperm samples obtained from the caput epididymis and vas deferens of virgin males. Curiously, contaminating extracellular DNA was associated with citrullinated histone H3, potentially resulting from a PAD-driven genome decondensation process. Taken together, our data emphasize the stability of cytosine methylation in mammalian sperm, and identify a surprising, albeit transient, period during which sperm are associated with extracellular DNA.


Sperm, DNA methylation, Epididymis, Genomics, Methylation, DNA isolation, Cytosine, Germ cells

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Copyright © 2021 Galan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

DOI of Published Version



Galan C, Serra RW, Sun F, Rinaldi VD, Conine CC, Rando OJ. Stability of the cytosine methylome during post-testicular sperm maturation in mouse. PLoS Genet. 2021 Mar 4;17(3):e1009416. doi: 10.1371/journal.pgen.1009416. PMID: 33661909; PMCID: PMC7963034. Link to article on publisher's site

Journal/Book/Conference Title

PLoS genetics

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Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.