title: The bHLH factors Xath5 and XNeuroD can upregulate the expression of XBrn3d, a POU-homeodomain transcription factor.
abstract: The basic helix-loop-helix (bHLH) factor Xath5 promotes retinal ganglion cell differentiation when overexpressed and may do so by regulating the expression of factors involved in the differentiation of these cells. Potential candidates include the Brn3 POU-homeodomain transcription factors, which have been implicated in retinal ganglion cell development. Here we have identified a new member of the Brn3 gene subfamily in Xenopus, XBrn3d. In situ hybridization analysis shows XBrn3d expression in developing sensory neurons and developing ganglion cells of the retina. Using a hormone-inducible Xath5 fusion protein, we have shown that in animal caps Xath5 can directly regulate the expression of XBrn3d. Since XBrn3d is also expressed in sensory populations where Xath5 is not expressed, we examined the regulation of XBrn3d expression by the bHLH factor XNeuroD. A XNeuroD-hGR fusion protein is similarly able to directly induce the expression of XBrn3d in animal caps. In addition, overexpression of XBrn3d by RNA injection promotes the expression of ectopic sensory neuronal markers in the lateral ectoderm, suggesting a role in regulating neuronal development. Therefore, Xath5 and XNeuroD can directly regulate the expression of a neuronal subtype-specific factor, providing a link between neuronal differentiation and cell fate specification.
authors.affiliation: Department of Neurobiology and Anatomy, University of Utah School of Medicine, Salt Lake City, Utah 84132, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Hutcheson
authors.forename: M L
authors.initials: ML
authors.lastname: Vetter
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005136:Eye Proteins / Q000235:genetics / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D018257:Helix-Loop-Helix Motifs; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D009475:Neurons, Afferent / Q000166:cytology / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D050818:Transcription Factor Brn-3; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D015854:Up-Regulation; D014981:Xenopus / Q000196:embryology / Q000235:genetics; D029867:Xenopus Proteins
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D009419:Nerve Tissue Proteins; D050818:Transcription Factor Brn-3; D014157:Transcription Factors; D029867:Xenopus Proteins; C109416:ATOH7 protein, Xenopus; C093564:Neurogenic differentiation factor 1