Increased epidermal growth factor expression produced by testosterone in the submaxillary gland of female mice is accompanied by changes in poly-A tail length and periodicity.
The level of mature EGF messenger RNA (mRNA) in the female submaxillary salivary gland (SMG) begins to rise after 3 days' treatment with testosterone (200 micrograms sc qod), and by 5 days it reaches a plateau of approximately 5 times baseline. Testosterone can increase the transcription of other genes in the SMG rapidly, so the lag in the EGF is not due to a slow androgen receptor response, and EGF mRNA can respond rapidly to other mediators, so the lag is not an innate characteristic of EGF transcription. Immunoreactive EGF levels reach a steady-state several times greater than the plateau reached by EGF mRNA, suggesting that testosterone also enhances the efficiency of EGF mRNA translation. Because testosterone has been reported to alter poly-A polymerase activities and because the translation and stability of some mRNAs is affected by changes in their polyadenylation, we used 3' rapid amplification of complementary DNA ends (3' RACE) to determine whether testosterone affected this aspect of EGF RNA metabolism. We found that EGF transcripts in untreated female SMG occur indistinct size classes, with poly-A tails of approximately 20, 50, 70, 100, and 200 A's attached after the terminal polyadenylation signal. In contrast, EGF transcripts in male SMG have poly-A tails of less clearly defined lengths, being more heterogeneous, ranging from approximately 20-100 A's. Treating female mice with testosterone causes the poly-A pattern in the SMG to change to a more heterogeneous population ranging from approximately 20-100 A's, similar to the male pattern. This change in EGF transcript polyadenylation occurs concurrently with the changes observed in the levels of EGF mRNA. EGF transcripts from male or female kidney contain distinct poly-A tails of approximately 20, 50, 70, 100, and 200 A's: neither EGF mRNA levels nor polyadenylation was altered by testosterone. The tissue-specific increase in EGF mRNA levels and in translational efficiency produced by testosterone in the female mouse SMG could involve this posttranscriptional alteration in transcript polyadenylation.