Characterization of GHRs, IGFs and MSTNs, and analysis of their expression relationships in blunt snout bream, Megalobrama amblycephala

- The six growth-regulating genes in M. amblycephala were characterized.
- The expression patterns of the six genes were analyzed in M. amblycephala.
- The expression relationships between the six genes were evaluated.

In order to test the hypothesis that the expression levels of GH/IGF axis genes would be negatively related to the expression of the myostatin genes in fish species, we cloned six growth regulating genes including growth hormone receptors-1/-2 (GHRs), insulin-like growth factors-I/-II (IGFs) and myostatins-a/-b (MSTNs) from blunt snout bream (Megalobrama amblycephala). The contents of mRNA transcripts for the six genes were determined in the different tissues of adult and developmental stages for the embryonic and larval periods. The results of quantitative real-time PCR showed that GHRs, IGFs and MSTNs were widely expressed in the tissues we tested, with the relatively lower expression levels in mesonephros, gonad and spleen for the six genes. The analysis of expression correlation coefficients among these six genes showed that GHR 1, GHR 2 and MSTN b were correlated with each other in adult tissues (P < 0.01). For the developmental stages, GHR 1 had a similar expression pattern to GHR 2 during the examined periods, both with the highest expression levels at 160 hpf (hours post-fertilization) (P < 0.05). IGF-II had higher expression levels than that of IGF-I before 400 hpf (P < 0.05), while IGF-I was active after 52 hpf. The maximum of MSTN a and MSTN b mRNA levels were at 24 hpf and 400 hpf, respectively. The analysis of expression correlation coefficients showed that GHR 1, GHR 2, IGF-I, IGF-II and MSTN b were positively correlated with each other during embryonic development (P < 0.01). The results from this study suggested that the relationship between GH/IGF axis genes and MSTNs was complex and not absolutely negative correlated in fish species.