Fig. 9. Proposed interactions between Flh, Ash1a, Ngn1 and other regulators during epiphysial neurogenesis. Flh has several distinct activities, it regulates its own expression (green solid arrow), and the expression of the bHLH transcription factors Ash1a and Ngn1 (in purple), which in turn activate lateral inhibition genes (in red), and the potential differentiation factors NeuroD, Otx5 and Onecut. Flh also activates TbxC expression independently of Ash1a and Ngn1 activity; the function of TbxC in the epiphysis is currently unknown (blue dashed arrow with a question mark). In addition, roles for Flh in the transcriptional regulation of lateral inhibition and differentiation genes, independent of the regulation of ash1a and ngn1 transcription, is inferred from analysis of the epiphysis in flh mutants (green dashed arrows with question marks, see text for details). Note that the early expression of ash1a is independent of Flh suggesting that another (as yet unknown) factor operates, possibly redundantly with Flh, to regulate bHLH gene expression at early stages (see Discussion).

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