Targeted inactivation of the phosphatidylserine receptor gene. (a) Ptdsr gene-targeting strategy. Homologous recombination in ES cells results in the deletion of exons I and II of the murine Ptdsr gene through replacement of a loxP-flanked neomycin phosphotransferase gene (neo), thereby ablating the reading frame of the encoded protein. Coding exons I-VI are shown as filled boxes, and deleted exons are colored green. Restriction sites are: A, AatII; B, BamHI; EI, EcoRI; EV, EcoRV; K, KpnI; R, RsrII; S, SacII; Sc, ScaI, X, XhoI. The probe sites are red boxes labeled: C, 5' outside probe; D, 3' outside probe. (b) Southern blot analysis of genomic DNA extracted from wild-type (+/+) and Ptdsr+/- (+/-) animals, digested with BamHI and hybridized with the 5' outside probe to confirm germ-line transmission of the mutant Ptdsr allele. 'Wild-type' indicates the BamHI fragment of 17.2 kb from the wild-type Ptdsr allele; 'mutant' indicates the BamHI fragment of 11.6 kb from the targeted Ptdsr allele. (c) PCR genotyping of embryos and animals from intercrosses of heterozygous Ptdsr+/- using a wild-type and a mutant allele-specific primer combination, respectively. (d) Northern blot analysis of total RNA isolated from E13.5 wild-type, Ptdsr+/- and Ptdsr -/- embryos. (e) Western blot analysis of protein from homogenates of E13.5 wild-type, Ptdsr+/- and Ptdsr -/- embryos using a Ptdsr-specific antibody. Developmental abnormalities at (f,g) E15.5 and (h) birth; in this and all subsequent figures wild-type littermates are located on the left and homozygous mutant mice on the right. The Ptdsr -/- embryos show exencephaly (f) or prosencephalic hernia in the forebrain region (arrowhead, neonate 2; h), uni-or bilateral absence of the eyes (f,g and neonate 2 in h, and arrow, neonate 3 in h), an abnormal head shape with proboscis (g), edema (arrowheads in f and g), and general anemia (asterisk, neonate 3 in h).