| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2006: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2005: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2004: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
During the histogenesis of the central nervous system, an enormous number of processes must be precisely executed according to the genetic program controlled by both cell-intrinsic and extrinsic factors. We have investigated the molecular mechanisms controlling laminated structures in the central nervous system using retina as a model system. Previously we have shown ; 1) Wnt2b, a secreted signaling molecule, can induce correct laminar formation from singly dissociated retinal progenitor cells in a rotation culture condition. 2) Wnt2b control proliferation and differentiation of the retina stem cells located in the ciliary marginal zones during normal development. In this research project, we further investigated downstream molecular cascade leading to the maintenance of the retinal stem cells at the peripheral retina.
Firstly, we found that Wnt2b maintained the undifferentiated progenitor cells even under the conditions where Notch signaling was blocked, which has long been believed to
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play a role in maintaining undifferentiated state of retinal progenitor cells. Wnt2b downregulated the expression of multiple proneural bHLH genes independently of Notch signaling, and forced expression of Cath5 under the control of an exogenous promoter suppressed the negative effect of Wnt2b on neuronal differentiation. These result suggested that Wnt2b maintains the naive state of marginal progenitor cells by attenuating the expression of both proneural and neurogenic genes, thus preventing those cells from launching out into the differentiation cascade regulated by proneural genes and Notch.
To further investigate the precise molecular cascade that blocks the function of proneural genes, we carried out subtractive screening of the library derived from Wnt-responding and non-Wnt-responding cells. We obtained several genes that are activated in response to the activation of the Wnt signaling. We then examined the expression pattern of these Wnt-responding genes during development by in situ hybridization. Notably, many of these genes were actually expressed in the stem cell-containing ciliary marginal zones, supporting our hypothesis that Wnt signaling is operating in this specialized cell type. We also found that HES1, which has been recognized as a downstream effector of Notch signaling, is regulated by Wnt signaling in the retinal stem cells, and that HES1 activity was necessary and sufficient for the maintenance of retinal stem cells. Less
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