THE RAT B-50(GAP-43) PROMOTER DIRECTS NEURAL-PREFERRED EXPRESSION OF A REPORTER GENE IN XENOPUS-LAEVIS EMBRYOS

B-50 GAP-43) is a neural protein believed to be important for nerve fi ber growth and synaptic plasticity. To study the phylogenetic conserva tion of the mechanisms controlling the expression of the B-50 gene we have introduced a hybrid transgene consisting of 8.4kb of the rat B-50 promoter region fused to the bacterial reporter LacZ into one-cell Xe nopus embryos. The expression of this transgene was studied in various stages of Xenopus development. A characteristic mosaic pattern of bet a-galactosidase (beta-gal) expression was detectable in stage 16 embry o's in cells located in the neural plate. As development proceeds nume rous beta-gal expressing cells were observed in the neurectoderm of de veloping spinal cord, the brain vesicles and in the eye anlage. In add ition to cells located in the embryonic nervous system a small number of beta-gal positive cells was present in tissues from ectodermal (ski n cells) and mesodermal (cells in somites and notochord) origin. In co ntrast, a histone-1C promoter directed non-selective expression of Lac Z. These results demonstrate that the rat 8.4kb B-50 promoter region c ontains sufficient cis-acting information to direct neural-preferred g ene expression in Xenopus laevis embryos. The neural-preferred action of the rat B-50 promoter during early stages of amphibian neuroembryog enesis suggests a high degree of functional conservation of the mechan isms that govern the expression of die B-50 gene in vertebrate evoluti on.