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

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