Involvement of insulin-like growth factor-I in inner ear organogenesis and regeneration

The verterbrate inner ear is an excellent model system to study signalling mechanisms in embryonic development. During the last years, insulin-like growth factor-I (IGF-I) has attracted attention in relation to the regulation of inner ear ontogenesis. IGF-I and its high-affinity tyrosine-kinase receptor are expressed during early stages of inner ear development. IGF-I is a powerful mitogen for the otic vesicle, where it stimulates cell-division and mitogenic signalling cascades. Later in development, IGF-I also promotes survival and neurogenesis of the otic neurones in the cochleovestibular ganglion (CVG). The actions of IGF-I are associated with the generation of lipidic messengers and the activation of Raf kinase, which results in the rapid induction of the expression of the proliferative celt nuclear antigen (PCNA) and the nuclear proto-oncogenes c- fos and c-jun. Regulation of organogenesis involves a dynamic balance of the mechanisms regulating cell division, differentiation and death. A model is proposed where this balance is the consequence of the action of IGF-I and NGF, which converge in Raf activation or suppression. The combinatorial expression of Jun and Fos family members in particular domains of the otic vesicle would be the final result of such cascade. Some of these mechanisms may be also implicated in otic regeneration.Peer Reviewe

Genetic annotation of gain-of-function screens using RNA interference and in situ hybridization of candidate genes in the Drosophila wing

Gain-of-function screens in Drosophila are an effective method with which to identify genes that affect the development of particular structures or cell types. It has been found that a fraction of 2-10% of the genes tested, depending on the particularities of the screen, results in a discernible phenotype when overexpressed. However, it is not clear to what extent a gain-of-function phenotype generated by overexpression is informative about the normal function of the gene. Thus, very few reports attempt to correlate the loss- and overexpression phenotype for collections of genes identified in gain-of-function screens. In this work we use RNA interference and in situ hybridization to annotate a collection of 123 P-GS insertions that in combination with different Gal4 drivers affect the size and/or patterning of the wing. We identify the gene causing the overexpression phenotype by expressing, in a background of overexpression, RNA interference for the genes affected by each P-GS insertion. Then, we compare the loss and gainof-function phenotypes obtained for each gene and relate them to its expression pattern in the wing disc. We find that 52% of genes identified by their overexpression phenotype are required during normal development. However, only in 9% of the cases analyzed was there some complementarity between the gain- and loss-of-function phenotype, suggesting that, in general, the overexpression phenotypes would not be indicative of the normal requirements of the gene. © 2012 by the Genetics Society of America.Peer Reviewe