Growth and specification: fly Pax6 homologs eyegone and eyeless have distinct functions

Abstract

Development requires not only the correct specification of organs and cell types in the right places (pattern), but also the control of their size and shape (growth). Many signaling pathways control both pattern and growth and how these two are distinguished has been something of a mystery. In the fly eye, a Pax6 homolog (eyeless) controls eye specification together with several other genes. Now Dominguez et al.1 show that Notch signaling controls eye growth through a second Pax6 protein (Eyegone). In mice and humans the single Pax6 gene appears to encode both specification and growth controlling proteins through alternative mRNA splicing.

Regulation of the Pax6 : Pax6(5a) mRNA ratio in the developing mammalian brain

“…There is evidence that Pax6 and Pax6(5a) have different functions in vivo in both vertebrates [9-11] and invertebrates [12,13]. Studies of Pax6 - and Pax6(5a) -related genes in Drosophila melanogaster , ey/ toy and eyg/ toe , have shown that they promote, respectively, differentiation and proliferation of eye precursor cells [12,13].…”

“…Studies of Pax6 - and Pax6(5a) -related genes in Drosophila melanogaster , ey/ toy and eyg/ toe , have shown that they promote, respectively, differentiation and proliferation of eye precursor cells [12,13]. Overexpression of Pax6 and Pax6(5a) can alter the expression of different sets of genes in mammals [10,11].…”

Signaling circuitries in development: insights from the retinal determination gene network

“…In addition to the PAX6 orthologs Twin of eyeless (TOY) and Eyeless (EY), two Drosophila Pax6-like genes not found in vertebrates [eyegone (eyg) and twin-of-eyegone (toe)] may act in parallel to ey during eye formation (Jang et al, 2003). Recent results suggest EY and EYG play discrete, but coordinated, roles, with EY providing important eye-specification cues and EYG regulating eye growth (Dominguez et al, 2004) (reviewed by Rodrigues and Moses, 2004).…”

New insights from hemichordate genomes: prebilaterian origin and parallel modifications in the paired domain of the Pax gene eyegone

“…The inability to detect homologs in various well‐curated genomes of basal chordates and vertebrates suggests that eyg was lost during the early evolution of chordates. Noting the absence of eyg in vertebrates, it has been previously proposed that Drosophila eyg might be evolutionarily related to isoform 5a of vertebrate Pax6 (Jun et al, '98; Rodrigues and Moses, 2004; Yao and Sun, 2005). In the latter case, the PAI subdomain is assumed to be rendered nonfunctional by the insertion of 14 amino acids encoded on the differentially spliced exon (Epstein et al, '94).…”