Functional characterization of insulin-like growth factors in an ancestral fish species, the Shovelnose sturgeon Scaphirhynchus platorhynchus

Observations from the present study provide the first characterization of the GH-IGF axis in Shovelnose sturgeon Scaphirhynchus platorhynchus, an ancestral fish species. An initial characterization of steady-state IGF-I and IGF-II gene expression in multiple tissues was conducted using real-time RT-qPCR. Overall, the tissues had significantly different profiles of IGF-I gene expression, with the highest IGF-I expression observed in the liver. The highest IGF-II gene expression was also observed in the liver, with minimal or no detection in muscle. A comparison between IGF-I and IGF-II expression within individual tissues revealed higher levels of IGF-II than IGF-I mRNA in the spleen, stomach and trunk kidney, and higher levels of relative IGF-I mRNA expression in the intestine and muscle. The GH-IGF axis was further elucidated by observing the effects of exogenous GH on IGF-I and IGF-II expression in liver and muscle tissue. The results revealed a significant dose-dependent response of both hepatic IGF-I and IGF-II, and muscle IGF-I mRNA expression following rbGH administration. At the highest rbGH concentration (240 μg/g BW), IGF-I mRNA levels in liver and muscle peaked significantly at 48 h, indicating both hepatic and muscle IGF-I expression to be stimulated by GH. Hepatic IGF-II expression was also stimulated 48 h following rbGH administration. Expression of IGF-II mRNA was not inducible in the muscle. Few studies have evaluated the effects of exogenous GH on IGF expression in ancestral vertebrate species, and as such, this research provides valuable insight into the evolution of the somatotropic axis in vertebrates.