Molecular cloning of amyloid cDNA derived from mRNA of the Alzheimer disease brain: coding and noncoding regions of the fetal precursor mRNA are expressed in the cortex

To gain insight into factors associated with the excessive accumulation of β-amyloid in the Alzheimer disease (AD) brain, the present studies were initiated to distinguish between a unique primary structure of the AD-specific amyloid precursor mRNA vis a vis other determinants that may affect amyloid levels. Previous molecular cloning experiments focused on amyloid derived from sources other than AD cases. In the present work, the authors cloned and characterized amyloid cDNA derived directly from AD brain mRNA. Poly(A)+ RNA from AD cortices was used for the preparation of λgt11 recombinant cDNA libraries. An insert of 1564 nucleotides was isolated that included the β-amyloid domain and corresponded to 75% of the coding region and ≅ 70% of the 3'-noncoding region of the fetal precursor amyloid cDNA reported by others. On RNA blots, the AD amyloid mRNA consisted of a doublet of 3.2 and 3.4 kilobases. In control and AD cases, the amyloid mRNA levels were nonuniform and were independent of glial-specific mRNA levels. Based on the sequence analysis data, they conclude that a segment of the amyloid gene is expressed in the AD cortex as a high molecular weight precursor mRNA with major coding and 3'-noncoding regions that are identical to the fetal brain gene product