Pro-photoreceptor activity of chick neurogenin1.
OBJECTIVE
Better understanding of photoreceptor fate specification may lead to efficient production of photoreceptors for cell replacement studies. The authors investigated the role of proneural bHLH gene neurogenin1 (ngn1) in photoreceptor genesis using the chick retina.


METHODS
In situ hybridization was used to delineate the spatial and temporal pattern of ngn1 expression. RCAS retrovirus was used to drive overexpression of ngn1 in retinal cells, and siRNA was used to reduce ngn1 expression in loss-of-function experiments.


RESULTS
Chick ngn1 was transiently expressed during early phases of retinal neurogenesis, from embryonic day (E)3 to E6, with cells expressing ngn1 confined to the apical side of the retinal neuroepithelium. The time window and the anatomic location of ngn1 expression coincided with photoreceptor genesis and differed from those of other transiently expressed proneural bHLH genes, such as ash1, ath3, ath5, and ngn2. Most ngn1-expressing cells lacked BrdU incorporation and lacked phosphorylated histone H3. In low-density cell culture, ngn1 overexpression increased neuroD expression and expanded the photoreceptor population but reduced the ganglion population. Treatment of dissociated retinal cells with siRNA against ngn1 mRNA specifically reduced the photoreceptor population. Overexpression of ngn1 in the retina reduced the expression of ash1, ath5, chx10, and ngn2.


CONCLUSIONS
The data suggest that ngn1 participates in a complex transcriptional network and may play a role in guiding a progenitor cell to the photoreceptor pathway.
Yan
Run-Tao
RT
Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0009, USA.
He
Li
L
Wang
Shu-Zhen
SZ
D000818:Animals; D030161:Avian Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D001973:Bromodeoxyuridine / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D002642:Chick Embryo; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D020287:In Situ Nick-End Labeling; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D055495:Neurogenesis / Q000502:physiology*; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D012160:Retina / Q000196:embryology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000378:metabolism
D030161:Avian Proteins; D051792:Basic Helix-Loop-Helix Proteins; D001973:Bromodeoxyuridine; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering