Transgenic worms containing a signal peptide/ beta peptide 1-42 minigene (derived from the human Amyloid Precursor Protein, APP) driven by the
unc-54 promoter/enhancer produce intracellular immunoreactive beta peptide deposits that react with the amyloid specific dye thioflavin S. Animals containing an identical construct expressing the 1-40 version of the beta peptide (lacking two C-terminal amino acids) also produce immunoreactive beta peptide deposits, but these deposits do not react with thioflavin S. Recent experiments have been directed towards: 1) determining if the difference in thioflavin reactivity between transgenic lines expressing the 1-42 and 1-40 is due to quantitative or qualitative differences in the expressed peptide, 2) determining what the engineered signal peptide is (or isn't) doing in these constructs, and 3) investigating whether formation of thioflavin-reactive (amyloid) deposits can be enhanced by co-expression of human apolipoprotein E 4, which is strongly associated with increased Alzheimer's Disease susceptibility and has been postulated to directly interact with beta peptide to form amyloid. Quantitative ELISA assays done in collaboration with the lab of S. Younkin (Mayo Clinic) indicate that the failure of beta 1-40 peptide to make amyloid deposits is due to qualitative differences in the expressed peptide (not due to lower overall levels of peptide expression). However, both peptide versions also show evidence of N-terminal modification, raising questions about the role of the signal peptide in beta peptide expression, and complicating interpretation of the ELISA data. I have therefore generated a new series of transgenic constructs with the signal peptide replaced with an initiator methionine, employing
unc-119,
mec-7, and
unc-54 promoters. For currently unknown reasons, none of these lines express immunohistochemically detectable beta peptide. Extrachromosomal transgenic lines have also been constructed that coexpress an
unc-54/Apo E4 construct and either of the original
unc-54/signal peptide/beta peptide constructs. Although immunohistochemistry clearly demonstrates that these lines coexpress both proteins in muscle cells, significant enhancement of thioflavin S-reactive deposits has not been observed in the extrachromosomal lines examined so far. Integrated lines are currently being generated to more carefully examine the interaction of Apo E and beta peptide in this model system.