Wingless and Hedgehog signaling pathways regulate orthodenticle and eyes absent during ocelli development in Drosophila

Abstract

The homeobox gene orthodenticle (otd) controls the process of regional specification that takes place in the Drosophila eye-antennal disc during ocelli development. Mutations that reduce or abolish otd expression in the ocelli primordium give rise to ocelliless flies. We have identified the cis-regulatory sequence (ocelliless enhancer) that controls otd expression during ocelli development and studied its regulation at the molecular level. The ocelliless enhancer is initially activated by the combined action of Wingless (Wg) and Hedgehog (Hh) signaling pathways. Later, a positive autoregulatory feedback loop sets in to maintain otd expression. Moreover, we have analyzed the role of otd during ocelli primordium development and determined its involvement in the expression of the retinal determination gene eyes absent (eya). otd indirectly regulates eya in ocellar precursor cells through the inhibition of wg, an eya repressor, and the maintenance of hh expression in the ocelli primordium. Hh signaling is necessary for eya activation in ocellar precursor cells and this activation is mediated by the full-length activator form of the transcription factor Cubitus interruptus.

Understanding the Structural and Developmental Aspect of Simple Eye of Drosophila: The Ocelli

“…Optic lobe placode formation, eye-antenna disc morphogenesis [104] orthodenticle Ocellus Photoreceptor development. Essential for rhabdomere biogenesis [8] hedgehog Signalling in ocelli development. Progression of morphogenetic furrow involved in eye.…”

“…Progression of morphogenetic furrow involved in eye. [8] wingless Regulated by Otd during development of ocelli. Eye morphogenesis; Positive regulation of eye retinal cell death; eye pigmentation.…”

“…Eye morphogenesis; Positive regulation of eye retinal cell death; eye pigmentation. [8] homothorax Regulate Otd and eyes absent during ocelli development; maintains ocelli size. Formation of morphogenetic furrow.…”

“…The otduvi mutant results from partial deletion of enhancer region in eye. In 1996's, Royet and Finkelstein reported that otd regulates the combination of hedgehog (hh) and wingless (wg) expression [8,39]. During eye-antenna imaginal disc development otd acts as a target for hedgehog.…”

“…The lateral ocellus develops from two separate discs, while the median ocellus is a result of combination from the anlagen which is present in each of the two plates [6,7]. Ocelli shares many conserved genes and transcription factors with compound eye in terms of development [6][7][8][9]. Furthermore, ocelli is getting special attention because of its association with some parts of largest neurons in insect nervous system which builds a potential scope for researching on neuronal synaptic transmission and its development [10].…”