MALE-ASSOCIATED POLYPEPTIDE (MAP) EXPRESSION IN DIFFERENT COMPARTMENTS OF THE REPRODUCTIVE-SYSTEM OF THE MUSSEL MYTILUS-GALLOPROVINCIALIS -IMMUNOCYTOCHEMICAL AND WESTERN-BLOT STUDY

Mytilus mussels are characterized by annually repeated reproduction wh ich is associated with subsequent growth, morphogenesis, breakdown and redevelopment of the gonad and reproductive tract into mantle mesench yme. We present a description of the expression of the male-associated polypeptide (MAP; see Mikhailov et al. 1995) in different compartment s of the male reproductive system as well as in mantle gonad-supportin g tissue. MAP is expressed in both gonad and mantle structures in dyna mic patterns that show a substantial overlap in terms of dependence on the stage of gonad development/involution. In general, the total MAP concentration directly correlates with the volume of gonad tubule/duct structures but inversely correlates with mantle connective tissue cel l fraction. A maximum of MAP expression is reached in the fully ripe m ale gonad. MAP is localized around gonad tubules/ducts, in the gonoduc t epithelium, membranes of follicle-like structures as well as in the extracellular fiber-like structures of the mantle. However, we also de monstrate unique sites of MAP accumulation in the lumen of gonad folli cle-like tubules and in ductal fluid. The latter is characterized by a very high MAP concentration. MAP is also detected in sperm-containing cell suspension obtained by gonad biopsy which we interpret as a resu lt of the adsorption of MAP on mature spermatozoa. The results obtaine d should be taken into consideration in the interpretation of possible MAP functions since they seem to point to MAP as a major component of ductal (seminal) fluid of the male reproductive tract. It is likely t hat MAP is able to complement the processes of sperm terminal differen tiation and maturation. In addition, we demonstrate that the male-pred ominant character of MAP expression is restricted by gonad-containing tissues (i.e., mantle and visceral mass) only, although the polypeptid e is also detected in other somatic organs in both males and females.