title: Selective constraints on protamine 2 in primates and rodents.
abstract: BACKGROUND
  Protamines 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  Mature-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.
authors.affiliation: Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), c/Jose Gutierrez Abascal 2, 28006, Madrid, Spain. lena.lueke@mncn.csic.es.
authors.forename: Lena
authors.initials: L
authors.lastname: Lüke
authors.affiliation: Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), c/Jose Gutierrez Abascal 2, 28006, Madrid, Spain. maxitour@mncn.csic.es.
authors.forename: Maximiliano
authors.initials: M
authors.lastname: Tourmente
authors.affiliation: Department of Ecology, Genetics and Evolution, Universidad de Buenos Aires, Buenos Aires, Argentina. dopazoh@gmail.com.
authors.forename: Hernan
authors.initials: H
authors.lastname: Dopazo
authors.affiliation: Centro Nacional de Análisis Genómico (CNAG-CRG), Center for Genomic Regulation, Universitat Pompeu Fabra, Barcelona, Spain. serra.francois@gmail.com.
authors.forename: François
authors.initials: F
authors.lastname: Serra
authors.affiliation: Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), c/Jose Gutierrez Abascal 2, 28006, Madrid, Spain. roldane@mncn.csic.es.
authors.forename: Eduardo R S
authors.initials: ER
authors.lastname: Roldan
mesh_terms: D000818:Animals; D005075:Biological Evolution; D008297:Male; D052586:Mating Preference, Animal; D011323:Primates; D011479:Protamines / Q000235:genetics*; D012377:Rodentia; D012641:Selection, Genetic; D013077:Sperm Head / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology
chemical_list: D011479:Protamines; C068621:protamine 2