In this regard, contrasting results with those already mentioned regarding sequence‑specific sperm DNA distribution, have been reported by several groups during the past years (Table 1).
Interestingly,by using similar strategies for chromatin dissection and sequence analysis in human, mouse and bovine sperm, it has been shown that nucleosomes might be moderately retained at unique DNA sequences and regulatory regions (Table 1).
In contrast, a majority of sperm histones seemed to be localized to the nuclear periphery, within distal intergenic regions and introns, and associated with centromere and telomere repeats and retrotransposons (LINE and SINE; Figure 1).
Obtaining such different results following the same strategies could be due to a technical issue. Carone et al.
suggest in their study that promoter nucleosomes, although being less abundant in sperm, are more stable to MNase digestion.
In this regard, an extensive nuclear digestion of chromatin would degrade more abundant nucleosomes in gene deserts and thus reveal only those associated with regulatory regions.
This hypothesis seems to be consistent with the identification of distal DNase I‑hypersensitive regions characterized by an enrichment at CTCF‑binding sites, depletion in H3K4me3 and presence of H3K9ac and H4K12ac in human and mouse spermatozoa43,46 (Table 1).