NEUROSCIENCE: Midline Signals

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Science  15 Sep 2000:
Vol. 289, Issue 5486, pp. 1841c

Despite the overt differences between the crystalline, multifaceted eye of Drosophila and the monofocal, multilayered complexity of the vertebrate eye, the early steps in formation of these two different eye types show remarkable similarities.

Masai et al. find that zebrafish eyes display a molecular correlate of the morphogenetic furrow that sweeps across and imposes pattern on the developing fruitfly retina. In the Drosophila retina, neurogenesis is initiated through induction of the gene atonal, which encodes a transcription factor. Homologs of the atonal gene are found in various vertebrates and include the ath5 gene expressed in zebrafish retina. Analysis of the expression of ath5 in zebrafish mutants suggests that axial tissues, perhaps through the action of the gene one-eyed pinhead in medial tissues and more proximately through signals from the optic stalk, are responsible for inducing normal expression of ath5. If initial induction of ath5 expression at the point of conjunction with the optic stalk does not occur, cells more peripheral in the retina fail to differentiate. The results imply the existence of a wave of neurogenesis that spreads across the zebrafish retina, reliant on ath5 expression and propagated by local signals once it is initiated. — PJH

Neuron 27, 251 (2000).

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