Fig. 1. Generation of the Mab21l1-null allele. (A) Maps of the Mab21l1 locus, the targeting vector used for mutagenesis and the Mab21l1 targeted allele. White boxes represent the Mab21l1-coding region, the neo cassette and the DTA cassette. Black bars represent DNA fragments used as 5' and 3' probes for Southern blots; the sizes of restriction fragments detected are shown with lines. Arrowheads indicate the location of the primer pairs (primers m1F, m1R and neoR) used for PCR genotyping, with sizes of the PCR products given above. E, EcoRI; B, BamHI; K, KpnI; S, SalI. (B) Southern blots of tail DNA from progeny of heterozygous mice after KpnI and SalI digestion. Blots were probed with the 5' probe, a 3.0 kb KpnI-EcoRI fragment, or the 3' probe, a 1.3 kb BamHI-SpeI fragment. The endogenous KpnI fragment hybridizing with the 5' and 3' probes is 19 kb in length. Insertion of the neo cassette containing SalI sites reduced the KpnI fragments to 8.3 and 7.5 kb. (C) PCR genotyping of genomic DNA. Sizes of PCR products are indicated on the right. (D) Whole-mount in situ hybridization of Mab21l1 in E10.5 heterozygous and homozygous embryos. Note, Mab21l1 expression seen in the heterozygous embryo (left) is absent in the homozygote (right).