Fig. 8. G1-cyclin mRNA levels. Total RNA isolated from rat liver was analyzed for cyclin expression levels. Northern analysis was performed for cyclin D1 using subcloned PCR product as a probe (A, upper panel). rRNA levels on the ethidium bromide-stained gel were used as a loading control (A, lower panel). To confirm these results, multiplex semiquantitative RT-PCR was performed to assess cyclin D1 mRNA content at the three developmental time points analyzed by Northern blot (B). An additional experiment (C) was performed in which cyclin D1 mRNA content in single samples from an E19 fetal rat; from rat pups on postnatal (P) days 1, 4, 7, 14, and 28; and from a normal adult rat (Ad). This experiment also included analysis of RNA preparations from two adult rats that underwent partial hepatectomy (PH) or sham operation (S) 24 h before sacrifice. For these last three samples, the number of PCR cycles was reduced to keep amplification in the linear range. D, an experiment in which a parallel analysis was carried out for cyclin E.