M. Torrado, M.P. Espana, A.T. Mikhailov
Abstract:
The purpose of the study was to initiate the comparative analysis of molecular mechanisms of sexual dimorphism of the reproductive system in bivalve molluscs with different anatomical/morphological gonad compartmentalization and different patterns of reproduction.
The identification and characterization of "male associated polypeptide" (MAP) in the gonad of Mytilus galloprovincialis (Michailov et al, Comp. Biochem. Physiol., 1997, 118B: 197-208) allowed us to analyze MAP expression in male/female compartments which are morphologically fused in common gonad of hermaphroditic species, Pecten maximus and Aequipecten opercularis (Pectinidae). Mytilus MAP is a non-glycosylated polypeptide with apparent molecular weight about of 40 kDa, pl 5.6; it is characterized by carboxylesterase acitivty.
In P. maximus and A. opercularis, significant differences between SDS-PAGE patterns of male or female gonad compartments were detected. In particular, the polypeptide with apparent molecular weight similar to that of MAP (i.e., about 38 kDA) displayed sex-associated expression, and it was predominatingly detected in the samples of male gonad compartment. This 38 kDa-polypeptide (Pectinidae analog of MAP) revealed a positive immuno-blot reaction with a set of anti-MAP antibodies.
Complete blocking of spermatogenesis which we observed in the so-called spent male gonads of M. galloprovincialis, resulted in a significant decrease of MAP gonad concentration. This indicates that MAP expression could be regulated by signals coming from spermatogenic tissue. In P. maximus ripe gonad, MAP-like polypeptide (38 kDa), associated with male gonad compartment, was detected (by immunofluorescence) in gonad connective tissue, mainly around ductlike structures and follicles, but not in the lumen of gonad tubules; in spent gonad MAP it was not found.
Taken together, the results obtained indicate that, in spite of high anatomical/morphological divergence of the reproductive system in different species of bivalve molluscs, gonad compartmentalization/differentiation may be characterized by common mechanisms at the level of somatic protein expression associated with spermatogenesis.
(Developmental Biology Unit, Inst. of Health Science, Univ. of La Coruna, Campus de Zapateira s/n, l S071 La Coruna, Spain)