The shell formation mechanism of Turbo argyrostomus based on ultrastructure and transcriptome analysis

The gold shell inner layer of Turbo argyrostomus is extraordinary in Gastropoda, which have economic value and extremely important significance for biomineralization. However, the gene sets responsible for its shell formation and studies of shell biomineralization focused on gastropods remain poorly explored. Here we surveyed microstructure with scanning electron microscope (SEM), hematoxylin-eosin staining (HE) and Alcian blue staining-Periodic Acid-Schiff staining (AB-PAS), supplemented transcriptomic which provide genetic information for shell formation. The results illustrate that T. argyrostomus shell exhibits the prismatic-nacreous-prismatic (P-N-P) microstructure through SEM, and histological observation demonstrated two major cell types, including adipocytes and mucin cells. The transcriptomic analysis revealed 11 biomineralization genes, among which WAP (whey acidic protein), N66, and nacre like are believed to related with shell color and microstructure. Domain analysis was conducted on the mucin gene to obtain its function in T. argyrostomus, 25.20% biomineralization domain in central mantle (C) vs. foot (F) and 22.39% in edge mantle (E) vs F, supporting for the relationship between mucins and biomineralization, where mucins are considered as framework protein in shell formation. Moreover, this study has discovered that energy distribution differences between edge mantle and central mantle. These results could provide insights for further understanding biomineralization mechanism in Gastropoda.