Figure 6.

Serum prolactin levels are normal in Src knockout mice however, prolactin receptor expression is reduced. A) Blood was drawn from Src-/-, Src+/- and Src+/+ mice at P17 and L2. Prolactin levels were measured using a radioimmune assay and the amount of PRL plotted as the mean (± SEM) of 5 mice for each genotype at the indicated developmental stages. Welch's t test was used to evaluate the statistical significance (defined as P < 0.05). Src-/- to Src+/+ at P17 P = 0.26, Src+/- to Src+/+ at P17 P = 0.27. Src-/- to Src+/+ at L2 P = 0.89, Src+/- to Src+/+ at L2 P = 0.08. B) Total RNA was isolated from the number 4 mammary gland of wildtype and knockout mice at P18, L2, L9, and I 2; three mice were used per genotype and developmental stage. cDNA was synthesized from 1 μg of total RNA and quantitative RT-PCR was performed using primers and probe specific for the long isoform of the prolactin receptor. PRLR message levels were normalized to GAPDH for each sample and the graph represents the mean (± SEM) relative amount of the triplicate tissue samples. C) The number 4 mammary gland was removed from Src-/- and Src+/+ mice at P18 (lanes 1–6), L 2 (lanes 7–12) and L 9 (lanes 13–18). Three separate mice were used per genotype and developmental stage. Protein lysates were prepared as described in the Materials and Methods sections, and immunoblotting conducted to detect the total amount of PRLR expression (top panel), and the amount of actin, as a loading control (bottom panel).