Abstract
BackgroundProtamines are sperm nuclear proteins with a crucial role in chromatin condensation. Their function is strongly linked to sperm head morphology and male fertility. Protamines appear to be affected by a complex pattern of selective constraints. Previous studies showed that sexual selection affects protamine coding sequence and expression in rodents. Here we analyze selective constraints and post-copulatory sexual selection acting on protamine 2 (Prm2) gene sequences of 53 species of primates and rodents. We focused on possible differences in selective constraints between these two clades and on the two functional domains of PRM2 (cleaved- and mature-PRM2). We also assessed if and how changes in Prm2 coding sequence may affect sperm head dimensions.ResultsThe domain of Prm2 that is cleaved off during binding to DNA (cleaved-Prm2) was found to be under purifying selection in both clades, whereas the domain that remains bound to DNA (mature-Prm2) was found to be positively selected in primates and under relaxed constraint in rodents. Changes in cleaved-Prm2 coding sequence are significantly correlated to sperm head width and elongation in rodents. Contrary to expectations, a significant effect of sexual selection was not found on either domain or clade.ConclusionsMature-PRM2 may be free to evolve under less constraint due to the existence of PRM1 as a more conserved and functionally redundant copy. The cleaved-PRM2 domain seems to play an important role in sperm head shaping. However, sexual selection on its sequence may be difficult to detect until it is identified which sperm head phenotype (shape and size) confers advantages for sperm performance in different mammalian clades.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0588-1) contains supplementary material, which is available to authorized users.
Highlights
Protamines are sperm nuclear proteins with a crucial role in chromatin condensation
In these sperm proteins positive selection within the adhesion domain has been attributed to adaptations to sperm competition and fertilization environment in primates, while in mouse species positive selection could not be explained by sexual selection [44]
Unlike what was observed for Prm1, we did not find a relationship between sexual selection and arginine content in mature-protamine 2 (PRM2)
Summary
Protamines are sperm nuclear proteins with a crucial role in chromatin condensation Their function is strongly linked to sperm head morphology and male fertility. One of these selective forces, is known to affect sperm phenotype in males competing for the fertilization of ova [1] by driving adaptive changes of sperm morphology and function [2,3,4]. It is not yet clear how changes at the molecular level are linked to adaptations in sperm phenotype. This effect was described for seminal fluid proteins in butterflies and
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
