Fig. 1.

Generation of M₂−/− mice.A, Targeting strategy. Arrows MF13 andPR1 indicate the PCR primers used for homologous recombinant screening, and arrows MF26,MR22, and PR1 indicate PCR primers used for genotyping. BamHI (B),HindIII (H),EcoRI (R), and SmaI (S) sites relevant to the identification of homologous recombinant clones are shown together with the expected sizes hybridizable to the M₂ and the neoprobes. B, Hybridization with the M₂ probe showing a 5.5 kb band specific to the targeted allele (KO) and a 10.6 kb band derived from the wild-type allele (WT). C, Hybridization with the neo probe showing a 5.5 kb band specific to the targeted allele. D, Northern analysis showing mRNA levels of M₂ and M₄ in the brains of wild-type, M₂+/−, and M₂−/− mice. Note that the M₂ mRNA in the M₂+/− brain decreased to approximately half of the wild-type brain and was absent in the M₂−/− brain. The mRNA levels of M₄ are not different among the three genotypes. Bottom, Signals hybridized with a Gapd probe used as an internal control.