TISSUE-SPECIFIC EXPRESSION OF ISOASPARTYL PROTEIN CARBOXYL METHYLTRANSFERASE GENE IN RAT-BRAIN AND TESTIS

Isoaspartyl protein carboxyl methyltransferase (PIMT) is widely distri buted in mammalian tissues. Using a polymerase chain reaction-generate d 124-bp DNA fragment from brain cDNA as a probe, four different sizes (similar to 4.0, 2.5, 1.7, and 1.1 kb) of transcripts were detected w ith northern blot analysis. They were expressed predominantly in rat b rain and testis. The major transcripts were 2.5 and 1.7 kb in the brai n and 2.5 and 1.1 kb in the testis. One of the major transcripts speci fic to the testis (1.1 kb) was determined to study the structural diff erence of major transcripts in the two tissues. This testicular cDNA h ad neither the 5' (94 nucleotides) nor the 3' (594 nucleotides) end of previously reported brain cDNA corresponding to 1.7 kb. The mRNA leve ls and enzyme activities of different regions and developmental change s were examined in the brain. The mRNA levels and enzyme activities we re concomitantly high in cerebral cortex and hippocampus. Although the y increased rapidly similar to 30 days after birth in the testis and d ecreased in aged rats, they increased gradually after birth and remain ed high during the aging of the brain. Both structural and development al studies show that the expression of the PIMT gene in brain and test is is regulated in a tissue-specific manner.