STRUCTURE AND PROMOTER ANALYSIS OF THE GENE ENCODING THE MOUSE HELIX-LOOP-HELIX FACTOR HES-5 - IDENTIFICATION OF THE NEURAL PRECURSOR CELL-SPECIFIC PROMOTER ELEMENT

HES-5 is a mammalian basic helix-loop-helix factor that has a distant sequence homology to the product of the Drosophila pair-rule gene hair y. HES-5 mRNA is present exclusively in the developing nervous system, but its level decreases as neural differentiation proceeds. In this s tudy, to characterize the molecular mechanism of the neural-specific e xpression of HES-5 we isolated the mouse HES-5 gene. This gene consist s of three exons, and Southern blot analysis shows that it is a single copy gene. The transcription initiation site, determined by primer ex tension and reverse transcriptase-mediated polymerase chain reaction, is located 26 nucleotides downstream of a TATA box. Transient transfec tion analysis shows that the upstream region of the HES-5 gene can dir ect efficient expression in neural precursor cells and moderate expres sion in undifferentiated NCB20 neuroblastoma-brain hybrid cells but no t in glioma or fibroblast cells. The moderate level of expression in N CB20 cells decreases when differentiation into neuron-like cells is in duced. Further promoter analysis shows that this undifferentiated neur al-specific expression is mediated by the multiple GC stretches presen t in the HES-5 promoter. Gel mobility shift analysis suggests the pres ence of a neural precursor cell-specific protein that binds to the GC stretches. These results raise the possibility that HES-5 expression i n the developing nervous system is regulated by the GC stretch-binding protein.