Studies on the Indian catfish Clarias magur reveal Insulin-Like Growth Factor II to be the major type and its upregulation in high-growth performing fish

Abstract

Expression of three growth-associated genes, IGF-I, IGF-II and IGF acid- labile subu-nit (IGFALS), was compared between highest and lowest growth performing fami-lies of Clarias magur being genetically selected for growth. Only IGF-II and IGFALS showed 3.50- and 2.10-fold differential expression, respectively, in RNASeq data of five pooled tissues, brain, liver, muscle, kidney and gonads. Relative expression profil-ing in brain, liver and muscle by qPCR showed 3.4-fold and 2.8-fold upregulation of IGF-II in muscle and liver, respectively, in higher performing family compared with the lower ones, while IGF-I was invariant and also the less expressed gene in all tis-sues. IGFALS expression was found to vary in accordance with IGF-II. Genotyping of one non-synonymous SNP (valine to isoleucine) identified in IGFALS revealed a sig-nificantly higher frequency of the isoleucine genotype in the high- performing group. Present study shows that in magur, IGF-Is significantly expressed not only in the liver but also in the muscle. Unlike other teleosts like cyprinids and cichlids where IGF-I has been reported to be the major component in the somatotropic axis, IGF-II is seen to be the major type in catfish, as also reported in Channel catfish, and is upregulated in high- growth individuals.