Alzheimer's amyloid precursor protein mRNA without exon 15 is ubiquitously expressed except in the rat central nervous system

The expression of L-βA4 amyloid precursor protein (L-APP) mRNA, which is a splicing product excluding exon 15 of the APP gene, was investigated in various tissues of adult rats by a polymerase chain reaction analysis of reverse-transcribed RNA (RT-PCR). L-APP mRNA was ubiquitously expressed in all the examined tissues including the liver, kidney, heart, skeletal muscle, spleen, thymus, adrenal, stomach, submandibular gland, testis and ovary, except for the central nervous system (CNS) tissues such as the brain and spinal cord. The DNA sequence analysis of the RT-PCR products from adult rat liver showed an L-APP cDNA form, in which exon 14 was spliced from exon 14 to exon 16, and exon 15 of the APP gene was excluded. In addition, regarding as the brain and liver, L-APP mRNA expression was examined during the development of the embryonic stage. In the brain, no L-APP mRNA expression was detected even in the embryonic stage, whereas L-APP mRNA expression of the liver was still found in the embryonic stage. These results suggest that the splicing event excluding exon 15, which is exactly adjacent to exon 16 and exon 17 encoding the βA4 protein, would probably occur very rarely in the CNS and that the splicing of L-APP might already be regulated in the embryonic stage.