Figure 1.

(a) Ribonuclease protection analysis of PTHrP and cyclophilin transcripts in RNA from yeast (lane 1) and mammary glands from virgin PTHrP^lox/– (lane 2) and BLG-Cre/PTHrP^lox/– (lane 3) mice shows that PTHrP is normally expressed at low levels; therefore significant recombination has not yet taken place. (b) Ribonuclease protection of PTHrP and cyclophilin in RNA from mammary glands of lactating BLG-Cre/PTHrP^lox/– (lane 2) and PTHrP^lox/– (lane 3) mice. Yeast RNA (lane 1) was a negative control. The efficiency of BLG-Cre–mediated recombination is highlighted by the essentially complete lack of PTHrP RNA in the BLG-Cre/PTHrP^lox/– mammary glands. (c) PTHrP protein was undetectable (12 of 14) or drastically reduced (2 of 14) in milk from BLG-Cre/PTHrP^lox/– mice (mean 0.06 ± 0.04 nM, n = 14) compared with littermate PTHrP^lox/– controls (16.4 ± 4.1 nM, n = 9) as a result of the mammary-specific targeting of PTHrP gene deletion.