Neuronal differentiation and subtype specification in embryonic stem cells

Abstract

Neurogenesis occurs in all mammals throughout life in discrete region of newlinethe central nervous system (CNS). The process of neurogenesis starts newlinefrom cells called stem cells which can give rise to multiple lineages and cell newlinetypes that constitute a mature organ. Through the process of differentiation newlinestem cells give rise to neurons and glia. The pathway leading to newlinedifferentiation of stem cells to neurons and glial cells is still not well newlineunderstood. newlineIn the present study I have tried to delineate the molecular newlinemechanism behind the process of differentiation of embryonic stem (ES) newlinecells to form functional neurons. I have used ES cells as a model for this newlinestudy. From previous studies it has been known that the interaction of two newlinefactors the intrinsic determinants and the extrinsic signaling molecules play newlinean important role in the process of neuronal differentiation. To analyze the newlinerole of intrinsic determinants in this study I have demonstrated that during newlinethe process of neuronal differentiation, the expression of neurogenin2 newline(Ngn2) increases as human ES cells are differentiated towards the newlineneuroepithelial lineage. When embryoid bodies (EBs) are treated with the newlineneural inducers vasoactive intestinal peptide (VIP) or retinoic acid (RA), the newlineexpression of Ngn2 increased in EBs and in neurospheres (NS). However, newlinethe expression of Ngn2 was not homogenous in EBs. The TH (tyrosine newlinehydroxylase) positive neurons that were derived from VIP or RA exposed newlineEBs correlated with the proportion of Ngn2 positive cells that were present newlinein EBs and NS. This suggests that Ngn2 plays a role in determining newlinedopaminergic neuron phenotype during the process of neuronal newlinedifferentiation. newline newlineThe role of extrinsic factors was studied during differentiation of hES newlinecells into serotonin neurons. Differentiation of stem cells into serotonin newlineneurons has not been well characterized. Homogeneous neural progenitors newlinewere isolated from differentiating hES cells. These homogeneous neural newlineprogenitors were differentiated into serotonin containing neuro