Purchase this article with an account.
Scott M Taylor, Karen Alvarez-Delfin, Carole Saade, James M Fadool, Peter F Hitchcock; The bHLH transcription factors Ascl1a and NeuroD function in a regulatory feedback loop with the Notch pathway to regulate proliferation of photoreceptor progenitors. Invest. Ophthalmol. Vis. Sci. 2014;55(13):719.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Development of photoreceptors in the vertebrate retina requires precise regulation of cell cycle entry and exit. In the retina of the embryonic zebrafish, the bHLH transcription factor NeuroD mediates exit of photoreceptor progenitors from the cell cycle (Ochocinska and Hitchcock, 2009). The purpose of this study was to determine the mechanisms through which NeuroD governs photoreceptor genesis in the zebrafish retina.
First, genetic mosaic analysis was performed to determine if NeuroD functions cell autonomously in the developing retina. Second, morpholino-induced NeuroD loss-of-function (LOF) was used in combination with in-situ hybridization and qRT-PCR to determine which molecules/pathways are regulated by NeuroD. Third, LOF approaches were used for putative target proteins to experimentally test the hypothesized relationships with NeuroD and with each other.
Genetic mosaic analysis revealed that NeuroD functions non-cell autonomously in the developing retina, and therefore subsequent experiments were focused on identifying mechanisms that could mediate this function. In-situ hybridization and qRT-PCR revealed that expression of notch1a, her4, ascl1a and hes6 increase following NeuroD LOF. Inhibition of the Notch pathway using the gamma secretase inhibitor DAPT rescued the NeuroD LOF phenotype and restored ascl1a expression to normal levels. Ascl1a LOF resulted in the loss of neuroD expression, increased Notch pathway activity, and increased ascl1a expression. Both Ascl1a and NeuroD LOF resulted in increased cyclinD1 and cyclinB1 expression, indicating a shared mechanism of cell cycle regulation.
Taken together, these data indicate that within photoreceptor progenitors the Notch pathway functions upstream of Ascl1a, which, in turn, governs the expression of NeuroD, which provides feedback inhibition onto the Notch pathway and ascl1a. The data also show that loss of Ascl1a maintains retinal progenitors in a proliferative, undifferentiated state and that Ascl1a strongly regulates its own expression.
This PDF is available to Subscribers Only