Eukaryotic initiation factor eIF6 modulates the expression of Kermit 2/XGIPC in IGF-regulated eye development

The eukaryotic initiation translation factor eIF6 is a highly conserved, essential protein implicated in translation. eIF6 is regulated in vivo by extracellular signals, such as IGF signaling (for a review see Miluzio et al., 2009). In Xenopus, eif6 over-expression causes a delay in eye development (De Marco et al., 2011). In this study we showed that eif6 co-immunoprecipitates with the insulin-like growth factor receptor (igfr) and may function downstream of igf in eye formation. The relationship between eif6 and gipc2, a protein partner of a variety of molecules including membrane proteins, was investigated. gipc2 is required for maintaining igf-induced aid activation on eye development (Wu et al., 2006). Significantly eif6 and gipc2 have opposite effects in eye development. While eif6 is required for eye formation below threshold levels, gipc2 knockdown impairs eye development (De Marco et al., 2011; Wu et al., 2006). In this study, it was shown that in eif6 over-expressors, the delay in eye morphogenesis is reversed by gipc2 injection, while the injection of eif6 down-regulates gipc2 expression. Real-time-PCR indicates that eif6 regulates gipc2 expression in a dose-dependent manner. In contrast, gipc2 knockdown has no significant effect on eif6 mRNA levels. These results suggest that eif6 regulation of gipc2 enables correct morphogenesis of Xenopus eye and stimulate questions on the molecular network implicated in this process.