Characterization and functional analysis of a chitin synthase gene (HcCS1) identified from the freshwater pearlmussel XXXX .

@entity3689 @entity1573 @entity31169 @entity35374
The triangle sail mussel, @entity31169 , 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 @entity31169 , and analyzed its possible physiological function. The complete ORF sequence of HcCS1 contained 6903 bp, encoding a 2300- @entity3689 protein (theoretical molecular mass = 264 kDa; isoelectric point = 6.22), and no putative signal peptide was predicted. A @entity35374 motor head domain, a CS domain, and 12 transmembrane domains were found. The predicted spatial structures of the @entity35374 head and CS domains were similar to the electron microscopic structure of the heavy meromyosin subfragment of @entity1573 smooth muscle @entity35374 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 @entity35374 head domain.
