Fig. 1. Targeted disruption of Math5. (A) Homologous recombination between 2.3 kb and 4 kb vector arms resulted in replacement of the bHLH domain (contained within the SmaI fragment) with a PGK-neo cassette and insertion of cytoplasmic ß-gal near the N terminus of Math5. Positions of the single-copy probe and PCR primers are indicated. Primers A+A' (5' arm) and B+B' (3' arm) were used for long-range PCR. (B) BamHI Southern analysis of littermate tail DNA obtained from an F₂ cross. (C) Internal PCR primers (D+D' for wild-type, C+C' for mutant) amplify allele-specific products from weanling tail DNA. (D) RT-PCR products (F+F') from E15.5 total eye RNA show the absence of Math5 mRNA and a great reduction of Brn3b mRNA in the Math5^-/- mutant, in comparison to ß-actin. B, BamHI; E, EcoRI; H, HindIII; S, SmaI.