Generation of a conditional IGF1R knockout in β cells. (a) A diagram of the Igf1r locus around exon 3 (filled square) is shown, followed by diagrams of the null (Igf1r^+/–) (41), floxed (Igf1r^lox) (42), and recombined floxed (Igf1r^Δlox) (42) alleles. The positions of the P1, P2, and P3 primers (arrows) used for genotyping are indicated. (b) PCR analyses using DNA from islets and control tissues. The lanes labeled – and + correspond to the negative and positive controls. Primers P1 and P2 yield a product of approximately 120 bp in WT and null Igf1r alleles, and 220 bp in the Igf1r^lox allele. In the Igf1r^Δlox allele, excision of exon 3 enables amplification to occur between primers P3 and P2, yielding 320 bp. In the lanes to the right of the markers, DNA from different tissues of Igf1r^Δlox/– mice was used. Br, brain; Li, liver; and Ki, kidney. (c) Western blot analysis of IGF1R expression. We obtained protein extracts from wild-type mouse embryonic fibroblasts or from fibroblasts derived from Igf1r^–/– mice as positive and negative controls (first two lanes on the left). We purified islets from wild-type (third lane from the left) and Igf1r^Δlox/– mice (right lane). Following detection of IGF1R, the blot was stripped and reprobed with anti-tubulin antiserum. The position of the various bands is indicated on the left of the autoradiogram.