ABSTRACT. Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan are found in a wide variety of organisms. These versatile biopolymers are associated with a broad range of biological functions. This article is the first to report the potential functions of 2 chitin metabolic enzyme genes from Hyriopsis cumingii. A chitinase-3 gene (Chi-3) and a chitin deacetylase gene (Cda) were cloned from H. cumingii and characterized. Semi-quantitative reverse transcription polymerase chain reaction analysis revealed that the Cda gene was expressed in blood, mantle, liver, stomach, kidney, intestine, gill, and foot, whereas Chi-3 was also expressed in those tissues but not in blood. The tissue-specific expression of H. cumingii Chi-3 indicated that other Chi genes may be involved in the H. cumingii immune system. Real-time quantitative polymerase chain reaction analysis showed that the expression of Chi-3 was significantly (P < 0.05) upregulated 12 h after shell damage, suggesting that Chi-3 might hydrolyze superfluous chitin after shell recovery and play a role in shell formation. Conversely, Cda expression did not change significantly (P 4540 G.-L. Wang et al. ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 11 (4): 4539-4551 (2012) > 0.05) to maintain a certain degree of acetylation in chitin/chitosan. This study enriches the basic research on chitin metabolic genes and lays foundations for further research of shell regeneration in mussels.
ABSTRACT. The triangle sail mussel, Hyriopsis cumingii, is the most important freshwater pearl mussel in China. However, the mechanisms underlying its chitin-mediated shell and nacre formation remain largely unknown. Here, we characterized a chitin synthase (CS) gene (HcCS1) in H. cumingii, and analyzed its possible physiological function. The complete ORF sequence of HcCS1 contained 6903 bp, encoding a 2300-amino acid protein (theoretical molecular mass = 264 kDa; isoelectric point = 6.22), and no putative signal peptide was predicted. A myosin motor head domain, a CS domain, and 12 transmembrane domains were found. The predicted spatial structures of the myosin head and CS domains were similar to the electron microscopic structure of the heavy meromyosin subfragment 19264-19274 (2015) of chicken smooth muscle myosin and the crystal structure of bacterial cellulose synthase, respectively. This structural similarity indicates that the functions of these two domains might be conserved. Quantitative reverse transcription PCR results showed that HcCS1 was present in all detected tissues, with the highest expression levels detected in the mantle. The HcCS1 transcripts in the mantle were upregulated following shell damage from 12 to 24 h post-damage, and they peaked (approximately 1.5-fold increase) at 12 h after shell damage. These findings suggest that HcCS1 was involved in shell regeneration, and that it might participate in shell and nacre formation in this species via chitin synthesis. HcCS1 might also dynamically regulate chitin deposition during the process of shell and nacre formation with the help of its conserved myosin head domain.
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