Tissue‐specific alternative mRNA splicing ofphenylethanolamine n‐methyltransferase (PNMT) duringdevelopment by intron RETENTION

• Published in: International journal of developmental neuroscience 1999-02, Vol.17 (1), p.45-55
• Main Authors: Unsworth, Brian R., Hayman, G.Thomas, Carroll, Amie, Lelkes, Peter I.
• Format: Article
• Language: English
• Subjects: alternative splicing; brain stem; corticosteroids; development; PC12 cells; phenylethanolamine N‐methyltransferase (PNMT); rat; sympathoadrenal lineage
• ISSN: 0736-5748; 1873-474X
• DOI: 10.1016/S0736-5748(98)00058-6

The expression of phenylethanolamine N‐methyl transferase (EC 2. 1.1.2.8,PNMT), the final enzyme in the cascade of catecholamine synthesis, is differentially regulated inadrenergic neurons in the brain and in adrenal chromaffin cells. Using reversetranscription‐polymerase chain reaction‐based techniques, we detected in the prenatal developingrat brainstem, two species of PNMT mRNA which were produced by a rare alternative splicingmechanism known as intron retention. The spliced, intronless message was downregulatedpostnatally, while the intron‐retained mRNA species continued to be constitutively expressedthrough adulthood. By contrast in the adrenals, at all stages of development examined, only theintronless message was expressed. In line with previous reports on the failure of glucocorticoidsto induce PNMT expression in the brain, the pattern of PNMT splicing in brainstem explants wasnot affected by the presence of the synthetic glucocorticoid dexamethasone. Undifferentiatedsympathoadrenal PC12 pheochromocytoma cells expressed very low basal levels of both mRNAvariants, accompanied by a very low basal PNMT enzymatic activity. Exposure of PC12 cells todexamethasone resulted in the upregulation of only the spliced mRNA variant concomitant with a3‐fold increase in PNMT enzymatic activity. In contrast, treatment of PC12 cells with nervegrowth factor (NGF) enhanced the expression of both the intron‐retained and the intronlessmRNA species without changes in the basal enzyme activity. This latter result suggests that thetranslation of the intronless mRNA species may be regulated by the intron‐retained mRNAspecies, which by itself may yield a truncated, yet enzymatically functional translational product.Our data suggest that the tissue‐specific regulation of PNMT expression is based on a rarealternative splicing mechanism termed intron retention, and that in the adrenal, but not in thebrain, this mechanism is sensitive to regulation by glucocorticoids. Thus, this system is uniquelysuited for studying the hormonal control of tissue‐specific splicing in the nervous system.