軟体動物の殻体形成機構のin vivoでの解明の試み

1殻体再生の初期段階における有機基質の形成と炭酸カルシウムの沈着の関係を明らかにすることを目的として,アコヤガイを試料として,in vitroでの軟体動物殻体再生実験および上皮組織培養実験が,in vivoでの結晶形成実験とともに行なわれた。2これらの実験の結果,石灰化初期段階に,MSI60と思われる不溶性膜成分が形成され,この不溶性有機基質膜問で,Sに富む可溶性有機基質と思われる成分の働きにより方解石結晶核が形成されるということが明らかになった。この事実は,compartment theoryを支持するととも,templateの存在をも暗示したため,template theoryをも支持する結果となった。3実験の最終段階で,方解石からなる稜柱層に類似の微細構造の形成が認められた。このことから,アコヤガイでは,真珠層の形成に先立って稜柱層の形成が必須であることが示唆された。Molluscan shell consists mainly of CaCO_3 with small amount of organic matrix. CaCO_3 crystals which have two polymorphs of aragonite and calcite, are arranged into specific direction and form microstructure with geometric alignment. Species used for this research are Pinctada fucata martensii, whose shells are composed of inner aragonitic nacreous and outer calcitic prismatic layers. Recent studies on molluscan biomineralization have been focused on the analysis of genes encoding organic matrix proteins, while in vivo and in vitro analysis of their functions should be clarified in future. In this research, we intend to elucidate the process of shell formation based on the experiment of shell regeneration, tissue culture and crystallizing experiment. As the result, several kinds of organic materials were observed on the cover glass which can relate to formation of crystal nucleus and shell microstructure. Additional observation was the formation of regenerated shell with different microstructure from the nacreous layer. X-ray diffraction analysis resulted in the formation of calcite instead of aragonite forming the nacreous layer. Observation of surface microstructure of the regenerated shell by scanning electron microscope showed similar structure to the prismatic layer. Needle-like microcrystals, containing high contents of sulphur were observed from the cultured epithelial tissues. These sulphurs were estimated to be derired from sulphur-containing glycoprotein, protein with high amount of Cys or sulfated protein. Finding of such sulphur-rich components will support the template theory about molluscan shell formation and further precise identification of the components will be the key for understanding crystal nucleation, control of crystal polymorphism and shell microstructure in the process of molluscan shell formation