CHARACTERIZATION OF THE 5' AND PROMOTER REGIONS OF THE GENE ENCODING THE MOUSE NEURONAL CELL-ADHESION MOLECULE F3

F3 is a 135 kDa neuronal cell surface adhesive glycoprotein belonging to the immunoglobulin supergene family (IgSF) which mediates heterophi lic contact formation among neural cells and is involved in the contro l of neurite growth. F3 expression is regulated, during critical devel opmental periods, on neuronal subpopulations thus suggesting that cont rol of F3 gene expression could be of morphogenetic relevance. To shed light on the mechanism involved in the control of F3 gene expression we isolated clones covering about 50 kilobases of the F3 gene which al so included the promoter region. The study of F3 gene exon/intron orga nization revealed that, like other neural IgSF molecules, each of the first two F3 C2 domains is encoded by two exons while the N-terminus, the signal peptide and the 5' untranslated region are each encoded by distinct exons. A single transcription start site was identified, surr ounded by a short 114 bp sequence able to direct reporter gene express ion in both F3-expressing and -non-expressing cells. In addition, a ce ll type-specific enhancer, only active in F3-expressing cells, was fou nd immediately upstream to it. structural analysis of the promoter reg ion revealed consensus sequences for binding transcription factors inv olved in cell type-specific and/or developmental regulations. Most of them are homeobox containing transcription factors thus suggesting tha t regulation of F3 gene expression could be part of a large developmen tal program.