Transcriptomic Analysis of the Shell Color Formation Mechanism in a Chinese Freshwater Snail Bellamya purificata

The freshwater gastropod, Bellamya purificata, is recognized for its ecological and economic importance. Nevertheless, the mechanism of shell color formation in the white shell of B. purificata remains unclear. This study aimed to investigate the molecular mechanisms underlying shell color differences by deeply sequencing the mantle tissue transcriptomes of blue-shelled and white-shelled B. purificata (BBPM, WBPM). Through bioinformatics analysis, genes were functionally annotated, and genes and metabolic pathways related to shell color formation were identified using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis. The results revealed significant differences in gene expression related to shell color formation. A total of 423 differentially expressed genes were detected, of which 224 genes specially were up-regulated in WBPM. Kyoto Encyclopedia of Genes and Genomes analysis of differentially expressed genes showed that the formation mechanism of the WBPM is related to tyrosine metabolism, tryptophan metabolism, arachidonic acid metabolism, the Notch signaling pathway, and porphyrin metabolism. The reduction in melanin synthesis and pigment deposition is likely the main reason for the white shell color formation in white-shelled snails B. purificata. The tyrosinase genes related to melanin synthesis and genes related to tryptophan metabolism significantly decreased in white-shelled snails B. purificata. Furthermore, reduced production of leukotriene C4 from arachidonic acid metabolism appeared to prevent pigment deposition, whereas endocytosis inhibited the Notch signaling pathway, further decreasing melanin synthesis. This study provides important information for understanding the mechanism of white shell color formation in B. purificata, laying a foundation for further research.