author(s)
Raju Ram and Chandan Haldar

abstract
Growth hormone-releasing hormone (GHRH) is an important neuroendocrine factor that stimulates the release of growth hormone (GH) from the anterior pituitary somatotrophs. Unlike in mammals, information on teleosts GHRH is insufficient. Here, GHRH full ORF (open reading frame) has been extracted from transcriptome data of Indian catfish, Clarias magur. It is a 423 bp transcript consisting of an ORF translatable to a 140 aa long polypeptide. This protein was shown to have apparent molecular weight (MW) of 16119.11 Da with pI of 6.61. The secondary structure of GHRH showed the presence of 17 αhelices, 27 coils and 10 β-sheets in the protein. The structural percentage of amino acid revealed that 37 amino acids (26.43%) have an alpha helix, 25 (17.86%) have extended strand, 10 (7.14%) have a beta turn, and 68 amino acids (48.57%) have random coil structures. Phylogenetically GHRH was closer to other catfishes like channel catfish and striped catfish. For homology modelling, pituitary adenylate cyclase activating polypeptide-38 (PDB id: 2d2p.1.A) was identified as suitable template. The alignment between our target GHRH and structural template was satisfied and predicted model showed high sequence similarity (58%). Relative mRNA expressions of GHRH in various tissues of different growth wise selected fish groups (i.e. high and low growth performing fishes) were estimated by using q-RT PCR analyses. It was abundantly expressed in the brain followed by male/female gonads of growth wise selected catfishes; demonstrating its possible functions may not be restricted to GH release only, but also in many other physiological and developmental regulations. Our results could be of great help to choose molecular marker like SNP or microsatellite engaged with this gene may contribute towards marker assisted selection for catfish significantly.