GENE TRAP INTEGRATIONS EXPRESSED IN THE DEVELOPING HEART - INSERTION SITE AFFECTS SPLICING OF THE PT1-ATG VECTOR

We describe the characterisation of three gene trap integrations in em bryonic stem cells in which the lacZ reporter gene is repressed by ret inoic acid (RA) in vitro and is expressed in the developing heart in v ivo. In one of these, the gene trap vector has integrated into a gene that is located on chromosome 17 and is homologous to the human transc ription factor gene, TFEB. Embryonic and adult cardiac expression of b oth the fusion transcript and the endogenous gene was confirmed. Howev er, we show that the integration has not resulted in a null allele, be cause wild type transcripts, possibly resulting from splicing around t he vector, are observed in homozygous tissue. The other two cardiac-ex pressing gene trap integrations have occurred into exons on chromosome s 1 and 5 and have used cryptic donor sites within the vector to gener ate functional fusion transcripts. One of these exon integrations resu lts in a lethal neonatal phenotype. (C) 1998 Wiley-Liss, Inc.