neurogenin2 elicits the genesis of retinal neurons from cultures of nonneural cells

Abstract

neurogenin2 (ngn2) encodes a basic helix-loop-helix transcription factor and plays an important role in neurogenesis from migratory neural crest cells. Its role in retinal development is poorly understood. We observed that in the developing chick retina, ngn2 was expressed in a subpopulation of proliferating progenitor cells. Ectopic expression of ngn2 in nonneural, retinal pigment epithelial cell culture triggered de novo generation of cells that expressed neural-specific markers and exhibited neuronal morphologies. Further molecular and morphological analyses showed that the main products of the induced neurogenesis were cells resembling young photoreceptor cells and cells resembling retinal ganglion cells. The generation of multiple cell types suggests that ngn2 induces various retinal pathways. Thus, unlike in the peripheral nervous system where ngn2 specifies one type of sensory neuron, ngn2 in the retina is likely involved in a common step leading to different cellular pathways. Our finding that ngn2 can instruct nonneural retinal pigment epithelial cells to differentiate toward retinal neurons demonstrates one possible way to induce de novo retinal neurogenesis.

A Role ofath5in InducingneuroDand the Photoreceptor Pathway

“…In fact, our previous studies showed that cultured RPE cells are responsive to the proneural activities of ngn2 and neuroD and may undergo neural transdifferentiation. Furthermore, the types of cells produced by RPE transdifferentiation agree with the retinal expression patterns of the proneural genes Wang, 1998, 2000b;Yan et al, 2001;Ma et al, 2004). In light of all this, RPE transdifferentiation toward retinal neurons might, at least to a certain extent, recapitulate the molecular events of retinal neurogenesis and offer an effective assay for proneural activities.…”

“…Previously we have shown that cultured RPE cells are responsive to the proneural activities of ngn2 and neuroD, and they may undergo transdifferentiation into cells that resemble photoreceptors and RGCs Wang 1998, 2000a,b;Yan et al, 2001). We found previously that retroviral-driven ectopic expression of chick ath5 promoted bFGF-initiated RPE transdifferentiation toward RGCs but alone was insufficient to induce such transdifferentiation .…”

“…The molecular mechanism underlying photoreceptor genesis has been subjected to intensive investigation but remains not well understood. Previous studies have implicated two basic helix-loop-helix (bHLH) genes, neurogenin2 (ngn2) and neuroD, participating in a genetic pathway leading to photoreceptor genesis (Yan and Wang, 1998;Marquardt et al, 2001;Yan et al, 2001). In the mouse retina, regions where Pax6 is inactivated lack ngn2 expression and contain no photoreceptor cells (Marquardt et al, 2001).…”

Acheate‐scute like 1 (Ascl1) is required for normal delta‐like (Dll) gene expression and notch signaling during retinal development

“…Studies of neurogenesis in Drosophila demonstrate that Delta is regulated by proneural bHLH transcription factors such as acheate-scute or atonal (reviewed by Skeath and Carroll, 1994;Bertrand et al, 2002). Many bHLH homologs are expressed in the vertebrate retina, but only Ascl1 and Neurog2 are expressed in mitotically active progenitors (Jasoni et al, 1994;Jasoni and Reh, 1996;Perron et al, 1998;Yan et al, 2001;Marquardt, et al, 2001;Ma and Wang, 2006;Le et al, 2006;Nelson and Reh, 2008). While the functions of proneural bHLH genes have been extensively investigated with respect to their role in retinal cell fate specification (reviewed by Cepko, 1999;Vetter and Brown, 2001;Yan et al, 2005;Ohsawa and Kageyama, 2007;Harada et al, 2007), their function in the regulation Notch ligands have not been described in the developing retina.…”

NeuroD induces the expression of visinin and calretinin by proliferating cells derived from toxin‐damaged chicken retina

“…The production and purification of viruses was done as described elsewhere (Yan and Wang, 1998;Yan et al, 2001). …”