Selective constraints on protamine 2 in primates and rodents.

Area of Science:

• Evolutionary biology
• Genetics
• Reproductive biology

Background:

• Protamines are essential sperm nuclear proteins for chromatin condensation, impacting male fertility and sperm head morphology.
• Sexual selection influences protamine gene sequences and expression, particularly in rodents.
• Selective constraints on protamine 2 (Prm2) and its role in male reproduction are complex.

Purpose of the Study:

• Analyze selective constraints and post-copulatory sexual selection on Prm2 gene sequences in 53 primate and rodent species.
• Investigate differences in selective constraints between primates and rodents for Prm2.
• Assess the impact of Prm2 coding sequence changes on sperm head dimensions.

Main Methods:

• Comparative sequence analysis of Prm2 across 53 primate and rodent species.
• Focus on selective constraints acting on cleaved-Prm2 and mature-Prm2 functional domains.
• Correlation analysis between Prm2 sequence changes and sperm head morphology (width, elongation).

Main Results:

• Cleaved-Prm2 is under purifying selection in both primates and rodents.
• Mature-Prm2 shows positive selection in primates and relaxed constraint in rodents.
• Cleaved-Prm2 sequence changes correlate with sperm head width and elongation in rodents.

Conclusions:

• Mature-Prm2's evolutionary freedom may stem from PRM1's conserved, redundant function.
• Cleaved-Prm2 plays a significant role in shaping sperm heads.
• Detecting sexual selection on Prm2 requires linking sequence changes to specific sperm phenotypes conferring performance advantages.