Purchase this article with an account.
R.-T. Yan, L. He, S.-Z. Wang; Pro-photoreceptor Activity of Chick Neurogenin1. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4012.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Understanding the "decision-making" process of photoreceptor genesis bears important clinical implications, as such knowledge is needed for efficient production of developing photoreceptors to be used in replacement therapies. This study investigates the role of proneural bHLH gene neurogenin1 (ngn1) in regulating photoreceptor production in the chick.
Chick ngn1 was RT-PCR amplified based on published information. In situ hybridization was used to delineate the spatial and temporal pattern of ngn1 expression. For functional study, RCAS retrovirus-driven overexpression of ngn1 in retinal cells was used in gain-of-function experiments and siRNA-mediated attenuation of ngn1 expression was used in loss-of-function experiments.
In the chick retina, ngn1 was transiently expressed during early phases of retinal neurogenesis, from embryonic day 3 (E3) to E6. Cells expressing ngn1 were localized to the apical side of the retinal neuroepithelium, an anatomical location of M-phase cells and newly born photoreceptor cells. Double-labeling showed that most ngn1-expressing cells were negative for phosphorylated histone H3, which identifies M-phase cells. Similarly, only a fraction of ngn1-expressing cells incorporated BrdU. Overexpression of ngn1 in the retina diminished the expression of ngn2 and ash1, two proneural bHLH genes involved in the production of various types of retinal cells. Infection of retinal progenitor cells with RCAS-ngn1 resulted in an expansion of photoreceptor population and a reduction in ganglion cell population. Notably, the changes were not observed in the retina, but with dissociated retinal cells cultured at low densities. This is not unexpected, because proneural genes are known to induce and then become the target of the Notch-delta mediated lateral inhibition, which is alleviated in low density cell culture. When dissociated retinal cells were cultured in the presence of siRNA against ngn1 mRNA, the photoreceptor population was specifically reduced.
The time window and the anatomical location of ngn1 expression coincided with photoreceptor genesis in the chick retina. Cells expressing ngn1 were likely undergoing the transition from proliferation to differentiation. Overexpression of ngn1 repressed bHLH genes involved in the production of different types of retinal cells and expanded photoreceptor population, while attenuation of ngn1 expression reduced photoreceptor production. These results suggest that ngn1 plays a positive role in photoreceptor genesis.
This PDF is available to Subscribers Only