Molecular cloning of type I collagen cDNA and nutritional regulation of type I collagen mRNA expression in grass carp

Grass carp (Ctenopharyngodon idellus) are important Chinese freshwater fish, and in China, the faba bean has been used as the sole food source for grass carp to transform them into crisp grass carp. Because of this, crisp grass carp has become an economically important fish because of its increased muscle hardness. To study the nutritional regulation of type I collagen in faba bean‐fed grass carp, we isolated type I collagen alpha 2 (COL1A2) on the basis of our isolation of COL1A1. The COL1A2 cDNA was found to be 4899 bp in length and included a 4059‐bp coding sequence (CDS) and encoded a polypeptide of 1352 AA. The protein peptide molecular weight was 127.39 kD, and the theoretical isoelectric point was 9.37. The COL1A2 protein possessed five α‐helixes, eight β‐sheets, 16 regions of triple helical repeats, 21 low‐complexity regions, 10 function domains and two zinc‐binding sites; however, no calcium‐binding sites were observed. The mRNA expression of COL1A1 and COL1A2 was assessed in eight tissues (muscle, hepatopancreas, intestine, gills, skin, fin, kidney and spleen) from grass carp and crisp grass carp by semi‐quantitative RT‐PCR. Expression of COL1A1 in the muscle, intestines and skin of crisp grass carp was higher than that in grass carp, and expression of COL1A2 in the muscle, gills, fin and skin of crisp grass carp was higher than that in grass carp. In the muscle of crisp grass carp, expression of COL1A1 and COL1A2 was higher than that in grass carp, which was further confirmed by real‐time PCR, and collagen content also was enhanced. These results demonstrated that type I collagen was closely related to the increased muscle hardness of faba bean‐fed grass carp.