Gene targeting strategy and verification. (A) An outline of the murine tau gene (around exon 9–11) is shown, as well as the targeting construct and the modified murine tau gene which was generated by homologous recombination. The null allele, lacking exon 10, was generated by breeding mice harbouring the modified murine tau gene with pgk-CRE transgenic mice. (B) Identification of the recombined allele in genomic DNA of embryonic stem cell (ES) clones 33 and 55 by PCR-analyses. Bands of expected sizes, 3.0 kbp (with primers a and b) and 4.0 kbp (with primers c and d) were detected in these clones, but not in ES clones 32 and 54. (C) PCR analysis with primers flanking the deleted chromosomal region (primers e and f). Amplification of genomic DNA from E10+/− mouse (E10) resulted in two distinct bands, a 900 bp band from the endogenous tau gene and a 460 bp band from the null allele. There was only a 900 bp band from the endogenous tau gene in wild-type mouse (wt). Positive (+) and negative (neg) controls for the PCR reactions. Empty lanes (−).