A model of retinal cell differentiation in the chick embryo.
This article presents an overview of retinal cell differentiation in the chick embryo, in the context of a hypothetical model based on information generated during the last several years. The model proposes that: (1) most (if not all) proliferating neuroepithelial cells have the potential to give rise to a progeny comprising two or more different cell types; (2) the time at which cells undergo their terminal mitosis does not determine their differentiated fate; (3) many postmitotic precursor cells remain plastic (i.e., uncommitted) for some time after terminal mitosis, during which they encounter position-dependent signals as they migrate toward their definitive laminar position within the retina; (4) as a consequence of these inductive stimuli, precursor cells that migrate to different retinal layers express different transcriptional regulators; (5) morphologically undifferentiated precursor cells are committed to cell type-specific, complex patterns of differentiation, which they can express even when isolated from their normal microenvironment, and (6) even after precursor cells become committed to a specific identity, additional inductive signals are necessary for the cells to complete the development of a fully mature phenotype. The article presents a summary of the supportive evidence, as well as a critical evaluation of the model, and concludes with an overview of unanswered questions regarding retinal cell differentiation and a brief evaluation of the prospects for further progress in this field.
Wilmer Eye Institute, The Johns Hopkins University, School of Medicine, MD, Baltimore, USA. radler@jhmi.edu
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D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002642:Chick Embryo / Q000166:cytology* / Q000502:physiology; D008938:Mitosis / Q000502:physiology; D012160:Retina / Q000166:cytology / Q000196:embryology*; D015398:Signal Transduction / Q000502:physiology; D013234:Stem Cells / Q000502:physiology