Morphological structure of shell and expression patterns of five matrix protein genes during the shell regeneration process in Hyriopsis cumingii

Abstract

Shell biomineralization is a process in which inorganic minerals assemble under accuracy control of macromolecule, mainly the matrix proteins. A shell-notching assay was used in Hyriopsis cumingii and CaCO3 deposition during shell regeneration and the expression pattern of five shell matrix protein encoding genes, HcTyp-1, hic31, hic52, silkmapin and Hcperlucin were analyzed. Macro- and microscopic observation revealed that shell regeneration can be broadly separated into three stages. (1) The formative period of the periostracum (from 0th day to 6thday), the pellicle formed and covered the gap creating a sealed space for mineralized layer origin. (2) The period of prismatic layer mineralization (from 14 to 21 days), the periostracum continued to grow, and aragonite seeds originated from the organic membrane accumulated and grew laterally to cover the whole periostracum. (3) The growth period of the nacreous layer (from 29 to 39 days), the initial nacreous layer formed, and regular aragonite crystals deposited, nucleated and eventually grew to form a distinctive brick wall structure. Furthermore, the periodic high-expression of five shell matrix protein genes during periostracum formation and prismatic or nacreous layer mineralization suggested they had a dominant role in the programmed reparative process. These observations contribute to understanding the molecular mechanism of shell formation.