Patterning of the Zebrafish Retina by a Wave of Sonic Hedgehog Activity

Abstract

The Drosophila retina is patterned by a morphogenetic wave driven by the Hedgehog signaling protein. Hedgehog, secreted by the first neurons, induces neuronal differentiation and hedgehog expression in nearby uncommitted cells, thereby propagating the wave. Evidence is presented here that the zebrafish Hedgehog homolog, Sonic Hedgehog, is also expressed in the first retinal neurons, and that Sonic Hedgehog drives a wave of neurogenesis across the retina, strikingly similar to the wave in Drosophila. The conservation of this patterning mechanism is unexpected, given the highly divergent structures of vertebrate and invertebrate eyes, and supports a common evolutionary origin of the animal visual system.

Zebrafish: A model system for the study of eye genetics

“…Differentiation then spreads dorsally around to the ventral temporal retina in a wave-like manner reminiscent of the movement of the morphogenetic furrow in Drosophila (Schmitt and Dowling, 1996). Also similar to Drosophila, the wave of differentiation is associated with a wave of sonic hedgehog expression by the differentiating cells (Neumann and Nuesslein-Volhard, 2000;Shkumatava et al, 2004). The similarities do not end there.…”

Cyclops‐independent floor plate differentiation in zebrafish embryos

“…A stable line was analysed with the green fluorescent protein (gfp) as reporter. The ShhGFP transgene (Neumann and Nü esslein-Volhard, 2000) contains 2.2 kb of shh upstream promoter sequence together with 5.8 kb comprising the intronic enhancers (Fig. 3A).…”

“…Double mutants were generated in the following allelic combinations: cyc tf219 / syu t4 , cyc tf219 /dtr tm276b , oep m134 / dtr tm276b , oep m134 /yot ty17a , smu b641 / cyc b426 . The ShhGFP transgene was described previously (Neumann and Nü esslein-Volhard, 2000).…”

Signal integration during development: Insights from the Drosophila eye

“…Intriguingly, while initiation and propagation of the MF was once thought to be an interesting but esoteric aspect of Drosophila development, studies in zebrafish suggest a similar strategy may be used in the developing vertebrate retina (Neumann and Nuesslein-Volhard, 2000). In the fish, photoreceptor differentiation initiates in the center of each prospective eye field and propagates radially outward (Neumann and Nuesslein-Volhard, 2000;Stenkamp et al, 2000;Russell, 2003).…”