The rat central nervous system expresses Alzheimer's amyloid precursor protein APP695, but not APP677 (L-APP form).

A novel splicing form of beta A4 amyloid precursor protein (APP) lacking exon 15, corresponding to 18 residues, was first reported in leukocytes and then in ubiquitous organs. To determine which APP molecules (APP695, APP751, or APP770) either with (N-APP) or without (L-APP; leukocyte-derived APP) exon 15 were expressed in various organs, we investigated the alternative splicing at exon 15 in the rat brain, kidney, heart, and testis by a PCR analysis of reverse-transcribed RNA and Southern blot analysis. Regarding APP695 without exons 7 and 8, L-APP was either seldom or never expressed in the brain, whereas both N- and L-APP were expressed in other organs. On the other hand, regarding APP751/770 containing exon 7, which codes for the Kunitz-type serine protease inhibitor domain, both N- and L-APP were expressed in all the organs examined, including the brain. These results suggest that a particular alternative regulation system related to exon 15 might be present in only APP695 of the brain and influence the proteolytic processing of APP.