High-resolution genetic maps and QTL mapping applications reveal polycystin gene involvement in oyster shell...

Genetic maps are efficient methods to study the molecular mechanisms of introgression and hybridization. The high-resolution genetic maps were constructed for Crassostrea hongkongensis and C. sikamea with reciprocal hybrid families. Thirty-five QTLs and twenty genes for shell height and shell length were identified, in which the polycystin gene was chosen for systematic study due to the highest LOD and phenotypic variance contribution. The polycystin expressions in two oyster species were highest at the blastula stage and upper mantle. In situ hybridization showed that polycystins were primarily found in the outer and middle folds of the mantle. Furthermore, the polycystin expression reached its highest peak at 24 h (C. hongkongensis) or 48 h (C. sikamea) after shell notch. The RNAi of polycystin resulted in sparse and disordered mineral layers and downregulation of other calcium-regulated genes. Conclusively, these results provided experimental support for the polycystin participating in shell formation and offered valuable molecular targets for further genetic analysis.