Insulin-like growth factor (IGF) signalling is required for early dorso-anterior development of the zebrafish embryo

Abstract

The insulin-like growth factor (IGF) signalling pathway has been highly conserved in animal evolution and, in mammals and Xenopus, plays a key role in embryonic growth and development, with the IGF-1 receptor (IGF-1R) being a crucial regulator of the signalling cascade. Here we report the first functional role for the IGF pathway in zebrafish. Expression of mRNA coding for a dominant negative IGF-1R resulted in embryos that were small in size compared to controls and had disrupted head and CNS development. At its most extreme, this phenotype was characterized by a complete loss of head and eye structures, an absence of notochord and the presence of abnormal somites. In contrast, up-regulation of IGF signalling following injection of IGF-1 mRNA, resulted in a greatly expanded development of anterior structures at the expense of trunk and tail. IGF-1R knockdown caused a significant decrease in the expression of Otx2, Rx3, FGF8, Pax6.2 and Ntl, while excess IGF signalling expanded Otx2 expression in presumptive forebrain tissue and widened the Ntl expression domain in the developing notochord. The observation that IGF-1R knockdown reduced expression of two key organizer genes (chordin and goosecoid ) suggests that IGF signalling plays a role in regulating zebrafish organizer activity. This is supported by the expression of IGF-1, IGF-2 and IGF-1R in shield-stage zebrafish embryos and the demonstration that IGF signalling influences expression of BMP2b, a gene that plays an important role in zebrafish pattern formation. Our data is consistent with a common pathway for integration of IGF, FGF8 and anti-BMPs in early vertebrate development.

Insulin-like growth factor-binding protein-3 inhibition of prostate cancer growth involves suppression of angiogenesis

“…The phenotype in embryos injected with the mutant form is essentially indistinguishable from that with wild-type IGFBP-3, indicating that the effect of IGFBP-3 on vasculogenesis is independent of IGF sequestration. These apparently dorsalized embryos resemble previously characterized Zebrafish mutants such as the notochord mutant ntl, which shows defects in notochord differentiation (Odenthal et al, 1996) as well as the dominant-negative IGF-1R overexpression mutant (Eivers et al, 2004).…”

Insulin-like growth factor signaling regulates zebrafish embryonic growth and development by promoting cell survival and cell cycle progression

“…Given recent reports for a role for IGF signaling in the induction of anterior neural tissue and patterning [15][16][17] , we tested whether igf1r MOs and dnIGF1R: GFP mRNA-injected embryos exhibited defects in patterning the central nervous system (CNS). Neither igf1r MOs nor dnIGF1R:GFP mRNA-injected embryos exhibited defects in CNS patterning, as indicated by the expression of otx2 (presumptive forebrain and midbrain), pax6b (eye field and forebrain) and shh (notochord) at 10 hpf.…”

“…The study by Richard-Parpaillon et al 16 used only one igf1r MO targeting one Xenopus igf1r gene. Pera et al 15 and Eivers et al 17 overexpressed a secreted form of a truncated IGF1R lacking both the transmembrane and intracellular domains. The lack of a transmembrane anchor may affect its effectiveness as a dominant-negative inhibitor because there are a family of secreted IGF-binding proteins (insulin-like growth factor binding proteins), which bind IGFs with equal or even greater affinity than the IGF1R.…”

“…32,33 We and others have previously shown that the zebrafish IGF ligands and IGF1Rs are highly expressed in almost all tissues and at all stages of embryogenesis. 14,17 In fact, IGF, IGF1R and IGFBP transcripts are detected even at the onecell stage. 3,14 It is, therefore, intriguing that the developmental arrest phenotype in IGF1R-deficient embryos did not occur until approximately 16 hpf.…”

“…15,16 A similar study in zebrafish was also reported. 17 Thus, there is a major discrepancy concerning the cellular basis for the conserved IGF1R signaling cascade during vertebrate development.…”