Oral Presentation HUPO 2019 - 18th Human Proteome Organization World Congress

Proteomic profiling of crocodile spermatozoa refutes the tenet that posttesticular maturation is restricted to mammals (#33)

David A Skerrett-Byrne 1 2 , Stephen D Johnston 3 , Matthew D Dun 4 5 , Brett Nixon 1 2
  1. Priority Research Centre for Reproductive Science, School of Environmental and Life Sciences, Faculty of Science, The University of Newcastle, Callaghan, NSW, Australia
  2. Pregnancy & Reproduction Research Program, Hunter Medical Research Institute, Newcastle, New South Wales, Australia
  3. School of Agriculture and Food Science, The University of Queensland, Gatton, Queensland, Australia
  4. Priority Research Centre for Cancer Research, Innovation and Translation, School of Biomedical Sciences and Pharmacy, Faculty of Health and Medicine, University of Newcastle, Callaghan, New South Wales, Australia
  5. Cancer Research Program, Hunter Medical Research Institute, Newcastle, New South Wales, Australia

Competition to achieve paternity has contributed to the development of a multitude of elaborate male reproductive strategies. In one of the most well-studied examples, the spermatozoa of all mammalian species must undergo a series of physiological changes, termed capacitation, in the female reproductive tract prior to realising their potential to fertilise an ovum. However, the evolutionary origin and adaptive advantage afforded by capacitation remains obscure. Here, we report the use of comparative and quantitative proteomics to explore the biological significance of capacitation in an ancient reptilian species, the Australian saltwater crocodile (Crocodylus porosus). Our data reveal that exposure of crocodile spermatozoa to capacitation stimuli elicits a cascade of physiological responses that are analogous to those implicated in the functional activation of their mammalian counterparts. Indeed, among a total of 1,119 proteins identified in this study, we detected 126 that were differentially phosphorylated (± ≥1.2 fold-change) in capacitated versus non-capacitated crocodile spermatozoa. Notably, this subset of phosphorylated proteins shared substantial evolutionary overlap with those documented in mammalian spermatozoa, and included key elements of signal transduction, metabolic and cellular remodelling pathways. Unlike mammalian sperm, however, we noted a distinct bias for differential phosphorylation of serine (as opposed to tyrosine) residues, with this amino acid featuring as the target for ~80% of all changes detected in capacitated spermatozoa. Overall, these results indicate that the phenomenon of sperm capacitation is unlikely to be restricted to mammals and provide a framework for understanding the molecular changes in sperm physiology necessary for fertilisation.

  1. Nixon B, Johnston SD, Skerrett-Byrne DA, Anderson AL, Stanger SJ, Bromfield EG, et al. Proteomic profiling of crocodile spermatozoa refutes the tenet that post-testicular maturation is restricted to mammals. Molecular & Cellular Proteomics. 2018:mcp.RA118.000904.