AUTHOR=Guo Xiaolin , Li Xixi , Zhao Feng , Liu Danwen , Yang Zujing , Li Moli , Li Yajuan , Wei Huilan , Wang Hao , Qin Zhenkui , Zhang Zhifeng , Bao Zhenmin 

TITLE=Full-length transcriptome analysis provides insights into larval shell formation in Mulinia lateralis

JOURNAL=Frontiers in Marine Science

VOLUME=9

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.1111241

DOI=10.3389/fmars.2022.1111241

ISSN=2296-7745

ABSTRACT=<p>Mollusca is the second largest animal phylum and represents one of the most evolutionarily successful animal groups. <italic>Mulinia lateralis</italic>, a small bivalve, is a promising model organism to facilitate studies of mollusc development. However, because of the lack of published genomic and transcriptomic resources, integrated research on the formation of larval shells in this species, which is a representative developmental process of molluscs and of great importance for larva survival, is hindered. In this study, the blastula, gastrula, trochophore larva, and D-shaped larva of <italic>M. lateralis</italic> were utilized for generating a comprehensive full-length transcriptome through Pacific BioSciences (PacBio) isoform sequencing (Iso-seq) and Illumina RNA-Seq. A total of 238,919 full-length transcripts with an average length of 3,267 bp and 121,424 annotated genes were obtained. Illumina RNA-Seq data analysis showed that 4,512, 10,637, and 17,829 differentially expressed genes (DEGs) were obtained between the two adjacent developmental stages. Functional annotation and enrichment analysis revealed the specific function of genes in shell biomineralization during different developmental stages. Twelve genes that may be involved in the formation of the larval shell of <italic>M. lateralis</italic> were identified, including <italic>insoluble shell matrix protein-encoding gene 1</italic> (<italic>ISMP1</italic>), <italic>ISMP2</italic>, <italic>ISMP5</italic>, <italic>chitin synthase</italic>, <italic>tyrosinase</italic>, <italic>chitin-binding protein</italic>, <italic>collagen</italic> and <italic>pu14</italic> involved in shell matrix deposition, and <italic>carbonic anhydrase</italic>, <italic>solute carrier family 4 member 8</italic> (<italic>slc4a8</italic>), <italic>EF-hand</italic>, and a calmodulin coding gene <italic>C-2442</italic> participated in ion transportation. In addition, calcium ion binding function, calcium signaling pathway, and endocrine and other factor-regulated calcium reabsorption pathways were significantly enriched. Weighted gene correlation network analysis (WGCNA) identified two modules related to biomineralization and larval shell formation, and <italic>slc4a8</italic> and <italic>ring finger protein 41</italic> (<italic>rnf41</italic>) were key hub genes that may be involved in this process. Moreover, it could be implied that the process of ion transport occurs earlier than the deposition of the shell matrix. This work provided a clear view of the transcriptome for <italic>M. lateralis</italic> and will be valuable in elucidating the mechanisms of larval shell formation as well as other developmental processes in molluscs.</p>