Microarray: a global analysis of biomineralization-related gene expression profiles during larval development in the...

The molluscan Pinctada fucata is an important pearl-culturing organism to study biomineralization mechanisms. Several biomineralization-related genes play important roles regulating shell formation, but most previous work has focused only on their functions in adult oysters. Few studies have investigated biomineralization during larval development, when the shell is initially constructed and formed until the juvenile stage in dissoconch shells. Here, we report, for the first time, a global gene analysis during larval development of P. fucata based on a microarray and reveal the relationships between biomineralization-related genes and the shell formation process.

Based on the P. fucata mantle transcriptome, 58,940 probes (60 nt), representing 58,623 transcripts, were synthesized. The gene expression profiles of the fertilized egg, trochophore, D-shaped, and umbonal stage larvae, as well as juveniles were analyzed by microarray performance. The expression patterns of the biomineralization-related genes changed corresponding to their regulatory function during shell formation. Matrix proteins chitin synthase and PFMG2 were highly expressed at the D-shaped stage, whereas PFMG6, PFMG8 and PfN23 were significantly up-regulated at the umbonal stage, indicating different roles regulating the formation of either periostracum, Prodissoconch I or Prodissoconch II shells. However, the majority of matrix proteins were expressed at high levels at the juvenile stage, and the shells comprised both an aragonitic nacreous layer and a calcitic prismatic layer as adults. We also identified five new genes that were significantly up-regulated in juveniles. These genes were expressed particularly in the mantle and coded for secreted proteins with tandem-arranged repeat units, as most matrix proteins. RNAi knockdown resulted in disrupted nacreous and prismatic shell layers, indicating their potential roles in shell formation.

Our results add a global perspective on larval expression patterns of P. fucata genes and propose a mechanism of how biomineralization-related genes regulate the larval shell formation process. These results increase knowledge about biomineralization-related genes and highlight new aspects of shell formation mechanisms.