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 us 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. (C) 2000 Elsevier Science Ltd. All rights reserved.