Instability of endogenous MRP/proliferin transcripts in the nucleus of mouse embryo fibroblasts contrasts with their stability when produced during transient transfections

Abstract

The mitogen regulated protein/proliferin (MRP/PLF) gene is transcribed in primary mouse embryo fibroblasts (MEFs), but the pre-mRNA is not properly converted into a stable cytoplasmic mRNA and instead is rapidly degraded, apparently in the nucleus [Malyankar et al. (1994): Proc Natl Acad Sci USA 91:335-359]. In 3T3 cells derived from the MEFs by the standard 3T3 immortalization protocol, stable MRP/PLF mRNA is produced. We show here that the processing of intron sequences is similar in the two cell types and that some of the MRP/PLF transcripts are polyadenylated in the MEFs. We also document the production of stable MRP/PLF mRNA generated by transcription of various plasmid constructs containing different portions of the MRP/PLF3 gene after calcium phosphate-mediated transfection into the MEFs. We conclude that the inability of the MRP/PLF mRNA to accumulate in the MEFs is unlikely to result solely from a single localized sequence in the primary transcript (or the mRNA) that causes it to be subject to rapid breakdown; possibly export of the mRNA from the MEF nucleus is defective or some aspect of the transcriptional process marks the transcript for degradation.

Intron 1 Elements Promote Erythroid-specific GATA-1 Gene Expression

“…Such effects of intron elements on transcription are not common, yet have been well documented in other systems. Examples include a tissue-specific reduction in mRNA stability upon the deletion of intron 1 of the ␣ 1 -collagen gene (36), attenuated nuclear export of mitogenregulated proliferin transcripts (37), and roles for intron 1-3 of the mouse thymidine kinase gene in markedly modulating transcript initiation (38). In the narrowed context of erythroid genes, several examples also exist wherein introns can regulate lineage-specific transcription.…”