title: The Australian saltwater crocodile (Crocodylus porosus) provides evidence that the capacitation of spermatozoa may extend beyond the mammalian lineage.
abstract: Although mammalian spermatozoa only acquire functional maturity as they are conveyed through the male (epididymal maturation) and female (capacitation) reproductive tracts, the degree of post-testicular development necessary to achieve fertilization in other vertebrate species remains far less clear. Indeed, despite reports that the epididymis of birds and reptiles is capable of secreting proteins that bind and modify the sperm surface characteristics, it remains unclear whether capacitation is a pre-requisite for fertilization in these species. Using the ancient reptilian Australian saltwater crocodile as a model, this study was undertaken to explore whether reptile sperm do undergo capacitation-like changes following ejaculation. Our studies revealed that crocodile spermatozoa experienced a rapid and sustained, cyclic-AMP mediated increase in progressive motility following incubation under conditions optimized for the induction of capacitation in mammalian species such as the mouse and human. This response was coupled with elevated levels of phosphorylation associated with both protein kinase A and tyrosine kinase substrates, the latter of which were predominantly localized within the sperm flagellum. In findings that also accord with mammalian spermatozoa, we confirmed a homologue of outer dense fibre 2 as one of the principal substrates for tyrosine phosphorylation. Overall, our findings support the concept that crocodile spermatozoa do undergo a process that is homologous to capacitation in preparation for fertilization of an ovum.
authors.affiliation: School of Environmental and Life Sciences, Discipline of Biological Sciences, The University of Newcastle, University Drive, Callaghan, New South Wales 2308, Australia brett.nixon@newcastle.edu.au.
authors.forename: Brett
authors.identifier: 0000-0003-2745-8188
authors.initials: B
authors.lastname: Nixon
authors.affiliation: School of Environmental and Life Sciences, Discipline of Biological Sciences, The University of Newcastle, University Drive, Callaghan, New South Wales 2308, Australia.
authors.forename: Amanda L
authors.initials: AL
authors.lastname: Anderson
authors.affiliation: Analytical and Biomolecular Research Facility, The University of Newcastle, University Drive, Callaghan, New South Wales 2308, Australia.
authors.forename: Nathan D
authors.initials: ND
authors.lastname: Smith
authors.affiliation: Koorana Crocodile Farm, Coowonga, Queensland 4702, Australia.
authors.forename: Robby
authors.initials: R
authors.lastname: McLeod
authors.affiliation: School of Agriculture and Food Science, The University of Queensland, Gatton, Queensland 4343, Australia.
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Johnston
mesh_terms: D000489:Alligators and Crocodiles; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D008297:Male; D019000:Phosphotyrosine / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D012661:Semen / Q000166:cytology*; D013075:Sperm Capacitation; D013081:Sperm Motility; D013094:Spermatozoa / Q000378:metabolism
chemical_list: D011506:Proteins; D019000:Phosphotyrosine; D017868:Cyclic AMP-Dependent Protein Kinases
keywords: capacitation; crocodile; fertilization; spermatozoa