The human breast and ovarian cancer susceptibility gene, BRCA1, encodes a protein of unknown function. Based on results from molecular analysis in human pedigrees, the BRCA1 gene product may be a tumor suppressor gene and, therefore, the mutant alleles are predicted to be null alleles or loss-of-function mutations. We are creating a mouse with a null allele at the BRCA1 locus. Using the published BRCA1 gene sequence, we synthesized probes corresponding to 1.5 kb of the 3.0 kb exon 11, which were used to screen a mouse 129Sv genomic library. Two overlapping genomic clones spanning about 23 kb were isolated. We demonstrated that the clones contain the mouse homolog of BRCA1. A 7.5 kb region from the mouse BRCA1 genomic clones was used to make a null allele targeting construct for this locus. A PGK-neo gene was inserted into the mouse BRCA1. The construct was linearized and introduced into TC1 ES cells by electroporation. We are currently analyzing the resistant ES clones for homologous recombinants.
