Molecular Analysis of Atypical Family 18 Chitinase from Fujian Oyster Crassostrea angulata and Its Physiological Role in the Digestive System

Transcriptome analysis of East Asian common octopus, Octopus sinensis, paralarvae

BACKGROUND

The genes involved in cephalopod development and their association with hatching and survival during early life stages have been extensively studied. However, few studies have investigated the paralarvae transcriptome of the East Asian common octopus (Octopus sinen sis).

OBJECTIVE

This study aimed to identify the genes related to embryonic development and hatching in O. sinensis using RNA sequencing (RNA-seq) and verify the genes most relevant to different embryonic stages.

METHODS

RNA samples from hatched and 25 days post-hatching (dph) O. sinensis paralarvae were used to construct cDNA libraries. Clean reads from individual samples were aligned to the reference O. sinensis database to identify the differentially expressed genes (DEGs) between the 0- and 25-dph paralarvae libraries. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to supplement the RNA-seq data for embryogenic developmental stages.

RESULTS

A total of 12,597 transcripts were annotated and 5,468 DEGs were identified between the 0- and 25-dph O. sinensis paralarvae, including 2,715 upregulated and 2,753 downregulated transcripts in the 25-dph paralarvae. Several key DEGs were related to transmembrane transport, lipid biosynthesis, monooxygenase activity, lipid transport, neuropeptide signaling, transcription regulation, and protein-cysteine S-palmitoyltransferase activity during the post-hatching development of O. sinensis paralarvae. RT-qPCR analysis further revealed that SLC5A3A, ABCC12, and NPC1 transcripts in 20 and/or 30 days post-fertilization (dpf) embryos were significantly higher (p < 0.05) than those in 10-dpf embryos.

CONCLUSION

Transcriptome profiles provide molecular targets to understand the embryonic development, hatching, and survival of O. sinensis paralarvae, and enhance octopus production.

Genomic and transcriptomic landscapes and evolutionary dynamics of molluscan glycoside hydrolase families with implications for algae-feeding biology

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Genome-wide characterization of GH families is conducted for Mollusca.

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GH9, GH10, GH18 and GH20 families are remarkably expanded in molluscs.

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The wide adoption of CBMs likely facilitates the hydrolysis of polysaccharides.

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Hepatopancreas is the main organ for the prominent expression of GH families.

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Functional divergence of GH families possibly contributes to their adaptive roles.

The hydrolysis of sugar-containing compounds by glycoside hydrolases (GHs) plays essential roles in many major biological processes, but to date our systematic understanding of the functional diversity and evolution of GH families remains largely limited to a few well-studied terrestrial animals. Molluscs represent the largest marine phylum in the animal kingdom, and many of them are herbivorous that utilize algae as a main nutritional source, making them good subjects for studying the functional diversity and adaptive evolution of GH families. In the present study, we conducted genome-wide identification and functional and evolutionary analysis of all GH families across major molluscan lineages. We revealed that the remarkable expansion of the GH9, GH10, GH18 and GH20 families and the wide adoption of carbohydrate-binding modules in molluscan expanded GH families likely contributed to the efficient hydrolysis of marine algal polysaccharides and were involved in the consolidation of molluscan algae-feeding habits. Gene expression and network analysis revealed the hepatopancreas as the main organ for the prominent expression of approximately half of the GH families (well corresponding to the digestive roles of the hepatopancreas) and key or hub GHs in the coexpression gene network with potentially diverse functionalities. We also revealed the evolutionary signs of differential expansion and functional divergence of the GH family, which possibly contributed to lineage-specific adaptation. Systematic analysis of GH families at both genomic and transcriptomic levels provides important clues for understanding the functional divergence and evolution of GH gene families in molluscs in relation to their algae-feeding biology.

Characterization of Free Fatty Acid Receptor 4 and Its Involvement in Nutritional Control and Immune Response in Pacific Oysters (Crassostrea gigas)

Free fatty acid receptor 4 (FFAR4) has various physiological functions, including energy regulation and immunological homeostasis. We examined the only FFAR4 homologue in the Pacific oyster Crassostrea gigas (CgFFAR4), which functions as a sensor of long-chain fatty acids. CgFFAR4 is 1098 bp long and contains a seven-transmembrane G protein-coupled receptor domain. CgFFAR4 expression was high in the hepatopancreas, but it was downregulated after fasting, indicating that it plays an essential role in food digestion. Lipopolysaccharide stimulation downregulated CgFFAR4 level, probably as an immune response of the animal. Reduced glycogen level alongside decreased insulin receptor, insulin receptor substrate, and C. gigas glycogen synthase transcription levels after CgFFAR4 knockdown revealed that CgFFAR4 was involved in the regulation of fatty acid and glycogen levels via the insulin pathway. Accordingly, this is the first study on an invertebrate FFAR and provides new insights into the role of this receptor in immune response and nutritional control.

Molecular cloning and functional analysis of chitinases in the fresh water snail, Lymnaea stagnalis

Molluscan shells, consisting of calcium carbonate, are typical examples of biominerals. The small amount of organic matrices containing chitin and proteins in molluscan shells regulates calcification to produce elaborate microstructures. The shells of gastropods have a spiral shape around a central axis. The shell thickness on the internal side of the spiral becomes thinner than that on the outer side of the spiral during the growth to expand the interior space. These observations suggest that a dissolution process works as a remodeling mechanism to change shell shape in molluscan shells. To reveal the dissolution mechanism involved in the remodeling of gastropod spiral shells, we focused on chitinases in the fresh water snail Lymnaea stagnalis. Chitinase activity was observed in the acetic acid-soluble fraction of the shell and in the buffer extract from the mantle. Allosamidin, a specific inhibitor of family 18 chitinases, inhibited the chitinase activity of both fractions completely. Homology cloning and transcriptome analyses of the mantle revealed five genes (chi-I, chi-II, chi-III, chi-IV, and chi-V) encoding family 18 chitinases. All chitinases were expressed in the mantle and in other tissues suggesting that chitinases in the mantle have multiple-functions. Treatment with commercially available chitinase obtained from Trichoderma viride altered the shell microstructure of L. stagnalis. Larvae of L. stagnalis cultured in allosamidin solution had a thinner organic layer on the shell surface. These results suggest that the chitinase activities in the shell and mantle are probably associated with the shell formation process.