Molecular characterization of two growth hormone receptor genes, and association analysis between microsatellite polymorphism and growth traits in the topmouth culter (Culter alburnus)

To better study the structure and function of the growth hormone receptor (GHR) of the topmouth culter, Culter alburnus, the DNA sequences of GHR1 and GHR2 were cloned based on mRNA data from the transcriptome of C. alburnus. Bioinformatics analysis was performed and the polymorphic microsatellite loci in the GHRs were tested in 120 samples which were bred in the same batch and cultured in the same pond. The full length of GHR1 cDNA is 3 498 bp, with an open reading frame (ORF) of 1 818 bp, and a 605 amino acid residue encoded protein. The full length of GHR2 cDNA is 1 743 bp, and with an ORF of 1 743 bp, and a 580 amino acid residue encoded protein, the amino acid sequences of GHR1 and GHR2 both comprised a signal peptide, extracellular region, transmembrane region, and intracellular region, and are 37.2% similar. There were marked differences in their structures. GHR1 has seven cysteine residues in its extracellular region of GHR1, but GHR2 has only five. GHR1 has three N-glycosylation sites more than GHR2. In the intracellular domain, there are 10 tyrosine residues in GHR1, but only 5 in GHR2, indicating that the two proteins may have different biological functions. Homologous amino acid sequence alignment showed that the GHRs are highly conserved with GHRs from other Cyprinidae. There were both 9 introns in the GHRs of C. alburnus, the length of intron 1 and 2 in GHR1 is over 10 kb so that they were not amplified in this experiment. Six microsatellite loci were found in the obtained sequence: the microsatellite locus (CT)₆ in the exon 2 of GHR1 was located in the signal sequence coding region, and no polymorphism of the (AC)₅ in intron 8 was detected; there were four microsatellite loci in GHR2, including (TG)₅ in intron 1, (TATC)₅(AT)₁₅(AC)₁₁(AT)₁₄(TG)₆ and (TA)₁₅ in intron 7, which belonged to highly polymorphic loci (PIC > 0.5). The (GAAG)₅ microsatellite loci in intron 6 was moderately polymorphic (PIC = 0.463). The number of genotypes detected using two microsatellite loci in intron 7 was 50 and 61, respectively, which had good potential for individual identification. Correlation analysis indicated that the four polymorphic microsatellite loci were all closely related to the growth traits. The cloning and the characterization of microsatellites of GHR gene may provide a reference for further study of its biological function and molecular marker assisted breeding in C. alburnus.