Psen1^tm2Psgh

A methionine to leucine missense mutation (M146L) was introduced into exon 6 via homologous recombination of a construct modified by PCR-mediated mutagenesis and containing a neomycin selection cassette approximately 150 bp into intron 6. The expected mutant transcript was undetected by Northern blot analysis, possibly due to the neo cassette affecting either expression or proper splicing. Low levels of transcript (0.5 to 1% of wild-type) were detected by RT-PCR analysis of RNA obtained from the brain and dorsal spinal cord, however no protein was identified by Western blot analysis. Accumulations of amyloid beta (A4) precursor protein (APP) fragments resulting from alpha- and beta-cleavage in the absence of gamma-cleavage further indicated the complete loss of normal protein expression. (J:80624)