Teosin, a novel basic shell matrix protein from Hyriopsis cumingii induces calcium carbonate polycrystal formation

In this study, a novel matrix protein (teosin) was isolated from Hyriopsis cumingii. Gene expression analysis showed that teosin is mainly expressed in the mantle and blood, and a hybridization signal was found in dorsal epithelial cells of the mantle pallial by in situ hybridization. Moreover, teosin expression during pearl formation indicated its participation in initial nacreous layer biomineralization, and suppressing teosin expression resulted in irregular crystal morphology and disordered arrangement in RNAi assay. In vitro crystallization assays indicated teosin could increase the size of calcite. By turning the sample stage about 15°, we got the high-resolution TEM images of the crystals' edges. This is a novel method to observe the crystal which is over 200 nm under TEM. In the control experiment group, the calcite show the character of long range order. The calcite induced by teosin were composed of nano-grains, and the polycrystal character were confirmed by EDS. These results suggested that teosin is involved in regulating crystal morphology regulation and inducing polycrystal formation during nacreous-layer formation.