Molecular and functional characterization of two distinct IGF binding protein-6 genes in zebrafish

Abstract

Insulin-like growth factor binding proteins (IGFBPs) are high-affinity binding partners for IGFs and play important roles in modulating IGF activities. In this study, we have identified and characterized two functional IGFBP-6 genes in zebrafish. Structural, phylogenetic, and comparative genomic analyses indicate that they are co-orthologs of the human IGFBP-6 gene. To gain insight into how the duplicated genes may have evolved through partitioning of ancestral functions, gene expression and functional studies were carried out. In adult fish, IGFBP-6a mRNA was most abundantly expressed in the muscle. The levels of IGFBP-6a mRNA in nonmuscle tissues were very low or barely detectable. In comparison, the levels of IGFBP-6b mRNA were high in the brain, heart, and muscle, but very low or undetectable in other adult tissues. During embryogenesis, the IGFBP-6a mRNA levels were relatively low. The IGFBP-6b mRNA levels were low during the initial 48 h. They became significantly higher at 72 and 96 h postfertilization. Overexpression of zebrafish IGFBP-6a and IGFBP-6b caused a similar degree of reduction in body size and developmental rate. No notable effects were observed on cell fate or patterning in these transgenic fish. These data suggest that the duplicated igfbp-6 genes encode two functionally similar proteins, but they have evolved distinct spatial and temporal expression patterns. These findings are consistent with the notion of an additional gene duplication event in teleost fish and have provided novel insight into the structural and functional evolution of the IGFBP gene family.

Insulin-like growth factor (IGF) signalling and genome-wide transcriptional regulation in fast muscle of zebrafish following a single-satiating meal

“…It is thought 15% of the duplicated genes or paralogues from this basal WGD have been retained in extant species (Jaillon et al, 2004). The distinct patterns of tissue expression and transcriptional regulation of many IGF system paralogues observed in zebrafish Chen et al, 2004;Zhou et al, 2008;Wang et al, 2009;Zou et al, 2009;Dai et al, 2010) is consistent with either subfunctionalization or neofunctionalization of these genes.…”

“…Activation of P13K-AKT-TOR stimulates a phosphorylation cascade that increases translation and protein synthesis (Engert et al, 1996;Duan et al, 2010) and inhibits protein degradation by the 26S proteasome system (Witt et al, 2005). In the zebrafish (Danio rerio), no fewer than 16 components of the IGF system have been described Chen et al, 2004;Zhou et al, 2008;Wang et al, 2009;Zou et al, 2009;Dai et al, 2010). The larger number of IGF components in zebrafish compared with mammals reflects a whole genome duplication (WGD) that occurred at the base of teleost evolution (Jaillon et al, 2004).…”

40 YEARS OF IGF1: IGF-binding proteins

“…In 583 contrast, overexpression of IGFBP-6 inhibited embryonic growth and development in zebrafish 584 (Wang, et al 2009). Transgenic mice overexpressing IGFBP-6 in the brain also were smaller during 585 the first post-natal month, and had cerebellar and reproductive abnormalities as well as abnormal 586 metabolic responses to a high fat diet (Bienvenu, et al 2004;Bienvenu, et al 2005).…”

Insulin-like growth factor binding proteins 4-6

“…These mice gained more weight and were more glucose-intolerant and insulin-resistant than control mice following a high-fat diet, suggesting that brain IGFBP-6 influences the regulation of energy homeostasis [83]. In zebrafish, overexpression of either of the duplicated IGFBP-6 genes inhibited embryonic growth and development [84].…”