Identification and expression of zebrafish Iroquois homeobox gene irx1

Iroquois homeoproteins are prepatterning factors that positively regulate p roneural genes and control neurogenesis. We have identified a zebrafish Iro quois gene, irx1, which is highly homologous to Xenopus Xiro1, Gallus c-Irx 1 and mouse Irx1. Expression of irx1 was initially detected at the bud stag e. By 16 h post-fertilization (hpf), irx1 expression was exclusively limite d to the prospective midbrain and hindbrain. By 24 hpf, irx1 expression was clearly detected in the acoustic-ovestibual ganglia, tectum, tegmentum, ce rebellum and rhombomere 1 but not in rhombomere 2 or mid-hindbrain boundary .