The Pax gene eyegone facilitates repression of eye development in Tribolium

We investigated the role of eyg during the postembryonic development of the red flour beetle Tribolium castaneum. Our results indicate conserved roles in antennal but not in eye development. Besides segmentation defects in the antenna, Tribolium eyg knockdown animals were characterized by eye enlargement due to the formation of surplus ommatidia at the central anterior edge of the compound eye. This effect resulted from the failure of the developing gena to locally repress retinal differentiation, which underlies the formation of the characteristic anterior notch in the Tribolium eye. Neither varying the induction time point of eyg knockdown nor knocking down components of the Janus kinase/Signal Transducer and Activators of Transcription signaling pathway in combination with eyg reduced eye size like in Drosophila.Taken together, expression and knockdown data suggest that Tribolium eyg serves as a competence factor that facilitates the repression of retinal differentiation in response to an unknown signal produced in the developing gena. At the comparative level, our findings reveal diverged roles of eyg associated with the evolution of different modes of postembryonic head development in endopterygote insects as well as diversified head morphologies in darkling beetles.Pax transcription factor family genes constitute an important part of the genetic toolkit that controls the development of the metazoan body plan including the visual system [1-3]. Four Pax genes have thus far been found to be important for Drosophila eye development: The tandem duplicated Pax6 orthologs eyeless (ey) and twin of eyeless (toy), which are critical regulators of early primordium specification and proliferation [4,5], the Pax2/5/8 paralog shaven (sv), which functions as the cone and pigment cell selector gene during retinal differentiation [6], and the Pax transcription factor gene eyegone (eyg), which has been discovered due to its essential requirement for retinal primordium growth [7