Comparison between epidermal growth factor, transforming growth factor-α and EGF receptor levels in regions of adult rat brain

Examination of adult rat brain regions by specific radioimmunoassays revealed a widespread distribution of transforming growth factor-α (TGF-α), but not epidermal growth factor (EGF), the peptide that had previously been reported to be present in rodent brain. Polyadenylated RNA samples from the different regions of rat brain were analyzed by Northern blot to identify mRNA species encoding precursor proteins for EGF (preproEGF), TGF-α (preproTGF-α), and the EGF/TGF-α receptor. The results indicate that TGF-α is the most abundant ligand for the EGF/TGF-α receptor in most parts of the brain analyzed. Message for preproEGF was only detectable after prolonged autoradiographic exposure; levels of preproEGF mRNA were between two and three orders of magnitude lower in brain than those expressed in control tissue (kidney), and one to two orders of magnitude lower than preproTGF-α mRNA levels in all brain regions. These results were confirmed by analysis of mRNA by RT/PCR, and support the hypothesis that expression of preproEGF mRNA in the brain is limited to smaller discrete areas, whereas preproTGF-α gene expression is almost ubiquitous.