Differential protein expression during sperm maturation and capacitation in an hermaphroditic bivalve, Pecten maximus (Linnaeus, 1758)

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Abstract

In order to investigate the mechanisms of final maturation and capacitation of spermatozoa in Pecten maximus, we used a 2D proteomic approach coupled with MALDI-TOF/TOF mass spectrometry (MS) and bioinformatics search against the Pecten database, to set up a reference map of the proteome of spawned spermatozoa, and identified 133 proteins on the basis of the EST database. These proteins are mainly involved in energy production, ion and electron transport (44%), cell movement (22%) and developmental processes (10%). Comparison between proteomes of spermatozoa collected before and after transit through the genital ducts of P. maximus led to the identification of differentially expressed proteins. Most of them are associated with energy metabolism (aconitate hydratase, malate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase), indicating important modifications of energy production during transit in gonoducts, potentially linked with acquisition of sperm motility. Three proteins involved in cell movement (Tektin-2, tubulin and microtubule-associated protein RP/EB family member 3) were down-regulated in spermatozoa stripped from the gonad. 40S ribosomal protein SA, involved in maturation of 40S ribosomal subunits, was also found to be down-regulated in spermatozoa obtained by induced spawning, suggesting reduction of the efficiency of RNA translation, a characteristic of late spermatozoon differentiation. These results confirm that maturation processes of P. maximus spermatozoa during transit through the gonoduct involve RNA translation, energy metabolism and structural proteins implicated in cell movement. Spermatozoa maturation processes clearly differ between P. maximus and gonochoric or alternately hermaphroditic bivalves, potentially in relation to reproductive strategies: the final maturation of the spermatozoon along the genital tract probably contributes to reduction of autofertilization in this simultaneously hermaphroditic species.

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