CLONING AND ANALYSIS OF A NEW DEVELOPMENTALLY-REGULATED MEMBER OF THEBASIC HELIX-LOOP-HELIX FAMILY

We have isolated a basic helix-loop-helix (bHLH) family member from an embryonic chick-brain cDNA library. This 3.86-Kb cDNA, GbHLH1.4, exhi bits extensive sequence similarity in the bHLH domain with Drosophila daughterless and the vertebrate cDNAs E12 and HTF4. Outside of the bHL H region the similarity is significantly reduced. GbHLH1.4 recognizes a 4.0-Kb mRNA and in situ hybridization analysis shows that GbHLH1.4 m RNA is widely expressed at early stages of development but becomes pro gressively restricted as embryogenesis proceeds. At later stages of em bryonic development, mRNA transcripts are localized to several structu res including the ventricular layers of the spinal cord and brain, the facial primordia, dorsal root ganglia and heart muscle and cardiac va lves. Strikingly, GbHLH1.4 expression in chick embryos exhibits signif icant overlap with that reported for the murine negative HLH regulator , Id.