Characteristics of chitin synthase (CHS) gene and its function in polyspermy blocking in the blood clam Tegillarca granosa

Abstract

In the artificial breeding of free-spawning marine bivalves, the sperm concentration is often far greater than that of eggs and, therefore, increases the risk of polyspermy. However, the molecular mechanism of polyspermy blocking remains unclear. The chitin synthase (CHS) gene has been reported to participate in polyspermy blocking in Caenorhabditis elegans; it was therefore cloned and analysed in the commercial bivalve Tegillarca granosa. The results showed that the CHS gene of T. granosa (TgCHS) was highly conserved with those of Atrina rigida, Leptochiton asellus, Pinctada fucata and Mytilus galloprovincialis. Similar to the CHSs of these species, TgCHS is characterized by three domains, A, B and C. Domain A was located at the N-terminus, containing 7-9 transmembrane helices. Domain B formed a central catalytic domain without any potential transmembrane segments. Domain C comprised the C-terminal end of the protein, containing multiple potential transmembrane segments. Treatment of oocytes of T. granosa with a CHS-specific inhibitor, nikkomycin Z, led to a significant increase in polyspermy, suggesting that TgCHS has a role in polyspermy blocking.