Molecular characterization of gonadotropin-releasing hormone receptor and its expression profiling in response to HCG stimulation in striped murrel, Channa striata (Bloch, 1793)

Abstract

The gonadotropin releasing hormone receptors (GnRHR) play an important role in the activation of GnRH and elicit the release of gonadotropins that plays an important role in maturation and spawning. In the present work, molecular characterization of the GnRHR gene of snakehead murrel, Channa striata was carried out. The full-length cDNA of GnRH receptors of the 1581 bp sequence, which encodes 440 amino acids was identified by RACE-PCR. Signal peptide analysis confirmed that GnRHR is a non-secretory protein, and hydropathy profiles indicated its hydrophobic nature. The deduced amino acid sequences of the GnRHR showed the expected conserved domains, which include seven membrane-spanning domains, two potential N-linked glycosylation sites (631 Asp, 561 Asp), and 32 sites phosphorylation sites of serine and threonine residues. A homology search of GnRHR cDNA sequence revealed 88 % identity with Channa argus, followed by 85 % and 83 % sequence identities with Lates calcarifer, and Anabas testudineus at the protein level. Phylogenetic analysis depicted a close association with Channa argus and other fish species. Our findings showed differential GnRHR expression during different reproductive stages, with higher expression after HCG administration. Expression profiling revealed that GnRHR is highly expressed in the brain and testis at 16 h post-HCG injection, while it was neutrally regulated in female ovarian tissues. This study provides full-length coding sequence information of the GnRHR gene and will help to understand the reproductive biology of murrel using expression studies and devise strategies for induced breeding.