RNase protection assays to quantitate hGH RNA levels in transgenic mouse skin at different ages. (A) RNAs were isolated from transgenic skin at birth (newborn, NB), and at 2.5 and 36 weeks postnatally. RNAs were also isolated from cultured transgenic mouse keratinocytes (Cell). RNase protection assays were carried out as described in the legend to Fig. 3, except that the specific activity of the radiolabeled mGAPDH antisense probe added to each sample was less than that used previously. Following hybridization and RNase treatment, the protected RNA fragments were resolved by electrophoresis through 6% acrylamide gels containing 8 M urea. (B) Phosphoimage analysis of blot in A. The amount of hybridizing radioactivity in each band was determined to obtain the ratio of protected hGH RNA relative to internal mGAPDH RNA in each sample. Relative to the level of mGAPDH RNAs in skin, the level of hGH transgene RNA did not vary significantly over time.