The pGt0Lxf gene trap vector contains a splice acceptor sequence upstream of a Beta-geo (beta-galactosidase/neomycin phosphotransferase II fusion) reporter gene; in this instance the splice acceptor was joined to a cryptic splice donor site in the vector intron, approximately 30 base pairs from the vector's 5' end, that was activated when the vector integrated into exon 6 of the gene. Transcription from the gene's endogenous promoter and splicing of the message yields a fusion mRNA joining endogenous upstream exons to the Beta-geo coding sequence. Beta-galactosidase is expressed in neurons of adult brain, strongly in caudate-putamen, olfactory tubercle, nucleus accumbens, thalamus, hippocampus and cerebellar Purkinje cells and more weakly throughout the remaining grey matter. (J:101748, J:146527)