| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥3,200,000 (Direct Cost: ¥3,200,000)
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| Research Abstract |
In the vertebrate, the retina region is specified in anterior neural plate and evaginates to form the optic cup, where six major classes of neurons and one-type of glia differentiate. Thus, the retina provides a good model, in which to study neuronal differentiation in the developing brain. Another interesting feature is that neuronal differentiation is initiated in one location and spreads to the whole region of the retina. In the compound eye of the invertebrate, the fruit fly, Drosophila melanogaster, cycle between activation of secretion factor, Hedgehog, and transcription factor, Atonal, is essential for progression of a neurogenic wave across the eye field. However, mechanisms underlying induction and progression of neurogenesis in the vertebrate retina is unknown.
To elucidate mechanisms underlying induction and progression of neuronal differentiation in the developing retina, we cloned zebrafish atonal gene, ath5, which expresses exclusively in newly differentiating retinal neur
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ons, In zebrafish, ath5 expression is initiated at nasal retina and spreads to dorsal and temporal region of the retina, suggesting that a wave of neuronal differentiation spreads from nasal to temporal in zebrafish. The nasal region is adjacent to the optic stalk tissue, raising a possibility that interaction between optic stalk and neural retina is important for initial induction of ath5 expression in the nasal retina. To test this possibility, the boundary between the optic stalk and the neural retina was ablated with focussed laser beam. This ablation disrupts initial induction of ath5 expression. Furthermore, transplantation of optic stalk tissue induces ectopically ath5 expression in temporal region of the retina. These data suggest that initial induction of neurogenesis is regulated by signals from optic stalk and that progression process is mediated by relays of short-range signals. These data suggest a striking similarity of regulation of a neurogenic wave between the vertebrate and Drosophila eye. Less
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