The Inhibition of Ocean Acidification on the Formation of Oyster Calcified Shell by Regulating the Expression of Cgchs1 and Cgchit4

Abstract

The biosynthesis of a calcified shell is critical for the development of oyster larvae. This process can be severely inhibited by CO 2 -induced ocean acidification, causing mass mortality of oyster larvae. However, the underlying molecular mechanism of such process has not been well explored until now. In the present study, a homolog of chitin synthase (named as Cg chs1) and a homolog of chitinase (named as Cg chit4) were identified from the Pacific oyster Crassostrea gigas . The cDNA sequences of Cg chs1 and Cg chit4 were of 813 bp and 2118 bp, encoding a putative polypeptide of 271 amino acids and 706 amino acids, respectively. There were a Chitin_synth_2 domain and a Glyco_18 domain in the inferred amino acid sequences of Cg chs1 and Cg chit4, respectively. Both Cg chs1 and Cg chit4 shared high sequence identity with their homologs in vertebrates. In addition, when oyster larvae were exposed to acidification treatment (pH 7.4), their shell biosynthesis process was seriously restrained. The expression level of Cg chs1 mRNA was significantly suppressed while that of Cg chit4 was dramatically activated upon acidification treatment. Cg chs1 and Cg chit4 are critical enzymes for chitin metabolism, and such changes in their mRNA expression could result in the decrease of chitin content in oyster larvae’s shells, which might lead to the failure of shell formation. Therefore, results in the present study suggested that acidified seawater might inhibit the formation of oyster calcified shell by suppressing the biosynthesis of chitin.

The Increased Expression of an Engrailed to Sustain Shell Formation in Response to Ocean Acidification

“…The total alkalinity in the pH 8.1, pH 7.8 and pH 7.4 groups was 2849.1 ± 14.5, 2416.3 ± 125.1, and 2110.6 ± 75.3 µeq kg −1 , respectively. And the partial pressure of CO 2 was about 658.1 ± 11.0, 1217.3 ± 11.6, and 2268.4 ± 50.1 ppm in pH 8.1, pH 7.8 and pH 7.4 treatment groups, respectively (Zhang et al, 2019). All the animal-involving experiments of this study were approved by the Ethics Committee of Dalian Ocean University.…”

“…After fertilization, the developing embryos were continuously observed by microscope until the second polar body was formed about 90 min post fertilization. Then, the embryos were transferred into an aquaculture tank containing 100 L aerated seawater of 20 • C (Zhang et al, 2019).…”

Ocean Acidification Triggers Cell Signaling, Suppress Immune and Calcification in the Pacific Oyster Larvae

“…Supplementary Table 4 provides complete literature of genes and pathways regulated in response to ocean acidification in marine bivalves across life stages. The expression levels of genes related to chitin synthesis was significantly decreased while the expression of genes related to chitin degradation was found to be increased in D shaped larvae of Crassostrea gigas at pH 7.4, negatively effecting chitin biosynthesis and hence biomineralization (Zhang et al, 2019). In adult pacific oyster, a series of calcium binding proteins and calcium signaling pathways were up-regulated in response to OA indicating regulation of calcium homeostasis under OA (Wang et al, 2020), also in larval sea-urchins (Evans et al, 2013) on the contrary, calcium dependent signaling pathway were suppressed in pearl oyster Pinctada fucata under low pH (Li et al, 2016b) but whereas in case of Crassostrea virginica, no significant expression of these genes was observed upon exposure to ocean acidification (Downey-Wall et al, 2020).…”

Metabolomic and transcriptomic profiling reveals the alteration of energy metabolism in oyster larvae during initial shell formation and under experimental ocean acidification

“…In the acidification treatment experiment, trochophores collected at 15 hours post fertilization (hpf) were equally divided into two groups, taking three replicates for each group. Larvae cultured in normal sea water (pH = 8.10 ± 0.05) was designated as the control group (Normal group), while those in the CO 2 exposure groups (pH7.7 and pH7.4 groups) were bathed in acidified seawater (pH = 7.40 ± 0.05) 32,33 . The pH value of the CO 2 Figure 7.…”