Progestin Signaling through an Olfactory G Protein and Membrane Progestin Receptor-α in Atlantic Croaker Sperm: Potential Role in Induction of Sperm Hypermotility

Abstract

Progestin stimulation of sperm hypermotility remains poorly understood despite having been described in numerous vertebrate species. We show here that progestin stimulation of sperm hypermotility in a teleost, the Atlantic croaker (Micropogonias undulatus) is associated with activation of an olfactory G protein (Golf). Furthermore, we provide evidence that this progestin action is mediated by membrane progestin receptor-α (mPRα). Golf was identified in croaker sperm membranes and was specifically activated after treatment with the progestin 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S). Treatment of sperm membranes with 20β-S caused an increase in cAMP production, which was blocked by pretreatment with cholera toxin and two membrane adenylyl cyclase inhibitors: 2′,5′-dideoxyadenosine and SQ22536. Moreover, preincubation of croaker sperm with 2′,5′-dideoxyadenosine and SQ22536 resulted in a significant inhibition of 20β-S-stimulated hypermotility. Binding of [3H]20β-S to sperm membranes was decreased after pretreatment with GTPγS but not pertussis toxin, suggesting the receptor is coupled to a pertussis toxin-insensitive G protein. Golf and mPRα were coexpressed on the sperm midpiece and flagella and were coimmunoprecipitated from sperm membranes. Finally, expression of mPRα protein on sperm increased after in vivo treatment with LHRH and was associated with increased induction of sperm motility by 20β-S. These results suggest that 20β-S activates mPRα in croaker sperm, which in turn activates Golf and membrane adenylyl cyclase to stimulate sperm hypermotility. Taken together these findings provide a plausible mechanism by which progestins stimulate sperm hypermotility in croaker and provide the first evidence of hormonal activation of Golf in any species.Progestin activation of an olfactory G protein pathway, likely through membrane progestin receptor alpha, is associated with induction of hypermotility in Atlantic croaker sperm.