KROX-20 IS A KEY REGULATOR OF RHOMBOMERE-SPECIFIC GENE-EXPRESSION IN THE DEVELOPING HINDBRAIN

The morphogenesis of the vertebrate hindbrain involves a transient seg mentation process leading to the formation of reiterated organisation units called rhombomeres (r). A number of regulatory genes expressed w ith a rhombomere-specific pattern have been identified, including the gene encoding the transcription factor Krox-20, which is restricted to r3 and r5. We have previously demonstrated that in r3 and r5 Krox-20 directly controls the transcription of Hoxa-2 and Hoxb-2. In the prese nt study, we provide evidence that Krox-20 is required for the express ion of another Hox gene, Hoxb-3, in r5 specifically. Furthermore, the regulatory role of Krox-20 is not restricted to the control of Hox gen e expression, since it is also involved in the activation of a recepto r tyrosine kinase gene, Sek-1, in r3 and r5 and in the repression of t he follistatin gene in r3 but not in r5. In conclusion, at least five regulatory genes belonging to different families are under the direct or indirect control of Krox-20 in r3 and/or r5 and this transcription factor therefore appears as a key regulator of gene expression in the developing hindbrain. (C) 1997 Elsevier Science Ireland Ltd.