Sperm Chromatin Status and DNA Fragmentation in Mouse Species with Diverging Mating Systems

Sperm DNA integrity and chromatin status serve as pivotal indicators of sperm quality, given their in-tricate link to sperm function, embryo development, and overall fertility. Defects in chromatin com-paction, which are often associated with compromised protamine content, can lead to damaged DNA strands. In this study, chromatin status and possible correlation with DNA damage was assessed in males of three mouse species: Mus musculus, M. spretus and M. spicilegus. We employed various staining methods, including aniline blue, methylene blue (Diff-Quik), toluidine blue and chromomy-cin A3, to assess chromatin compaction in cauda epididymal sperm. Samples were also analyzed by the sperm chromatin structure assay (SCSA) to estimate DNA fragmentation (%tDFI, %HDS). Analyses were carried out on freshly collected sperm and cells incubated for 3 h in a Hepes-buffered modified Tyrode's medium simulating conditions of the female reproductive tract. Notably, the analysis of chromatin status yielded minimal abnormal values across all three species, employing diverse meth-odologies. SCSA analyses revealed distinct variations in %tDFI between species. Following sperm incubation, the percentages of sperm stained with methylene blue exhibited differences among the species and were significantly correlated to the DNA fragmentation index. HDS demonstrated correla-tions with the percentages of sperm stained by aniline blue, methylene blue and chromomycin A3. Overall, chromatin compaction was high across all species, with limited differences among them. The relationship between chromatin status and DNA integrity appeared to be related to levels of sperm competition among species.