227. Eggs with a surprise: the ‘sperm-specific’ protein SPRASA is also expressed in the oocyte

Abstract

SPRASA is a newly identified protein which in silico analysis suggests is not expressed in other tissues. Antibodies reactive with SPRASA have been identified in some infertile men and an antiserum reactive with recombinant SPRASA prevented human sperm binding to hamster oocytes in vitro, indicating an important role in sperm/oocyte recognition. The aim of this study was to investigate the spatial and temporal expression of SPRASA in reproductive and other tissues. Brain, thymus, heart, spleen, kidney, liver and the reproductive organs from duplicate female and male Balb/C mice were collected at several postnatal timepoints. RNA was extracted, reversed transcribed and analysed by quantitative real time PCR for SPRASA expression. Abattoir-derived, in vitro matured, bovine oocytes were examined for SPRASA expression by fluorescent immunochemistry. To examine SPRASA binding sites on oocytes, matured bovine oocytes were exposed to biotinylated recombinant human SPRASA or biotinylated α-lactalbumin (control), then visualised by confocal microscopy using DTAF-conjugated streptavidin. We found SPRASA mRNA was expressed in the reproductive organs of both females and male mice from postnatal day 10. Fluorescent immunochemistry indicated SPRASA was expressed on the oolemmal membrane and in the few cumulus cells remaining attached to zona-intact oocytes. Control preimmune serum did not stain the oocytes or cumulus cells. Recombinant human SPRASA bound to the oolemmal membrane of both zona intact and zona free bovine oocytes. To date the expression of SPRASA has only been reported in the testes/sperm with an additional single EST identified in brain. Our quantitative real-time PCR analysis demonstrated SPRASA is also expressed in the female reproductive organs. This was confirmed by our immunoassays which show oocytes and possibly cumulus cells express SRPASA while the oolemmal membrane has the ability to bind (sperm-derived) SPRASA. That SPRASA expression is restricted sperm and oocytes confirms the likely function of this protein in reproduction.