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Negative bHLH transcription factor Hes1 can inhibit neural stem cells (NSCs) from precocious neurogenesis through repressing proneural gene expression; therefore,sustenance of Hes1 expression is crucial for NSC pool maintenance.Here,we find that Ids,the dominant-negative regulators of proneural proteins,are expressed prior to proneural genes and share an overlapping expression pattern with Hes1 in the early neural tube of chick embryos.Overexpression of Id2 in the chick hindbrain upregulates Hes1 expression and inhibits proneural gene expression and neuronal differentiation.By contrast,Hes1 expression decreases,proneural gene expression expands and neurogenesis occurs precociously in Id1 ; Id3 double knockout mice and in Id1-3 RNAi-electroporated chick embryos.Mechanistic studies show that Id proteins interact directly with Hes1 and release the negative feedback autoregulation of Hes1 without interfering with its ability to affect other target genes.These results indicate that Id proteins participate in NSC maintenance through sustaining Hes1 expression in early embryos.