Researchers from GenPharm International Inc. have produced atransgenic mouse that could serve as a small-animal model forstudying the etiology of Alzheimer's disease.
Reporting in today's issue of the Proceedings of the NationalAcademy of Sciences, Barbara Pearson and Ted Choidemonstrate that they have successfully introduced into micethe total genomic human DNA for amyloid precursor protein(APP), which is processed by the cell into the beta amyloidpeptide found in the senile plaques of patients withAlzheimer's.
Pearson and Choi are not the first researchers to createtransgenic mice carrying the human APP gene, but they are thefirst to use total genomic DNA for the experiments rather thancomplementary DNA (cDNA) constructs of the gene. Thedifference, according to Jonathan MacQuitty, GenPharm's chiefexecutive officer, is that genomic versions of the gene containall the naturally occurring control elements that allow thatparticular gene to be expressed properly, whereas syntheticcDNA constructs don't.
And since there appear to be at least five different isoforms (ordistinct transcripts caused by differential splicing) of the APPgene, only use of the total genomic DNA can allow for theirpresence in the brain of the transgenic recipient, MacQuittyadded.
The Johns Hopkins University researcher group, led by J.D.Gearheart, has recently published data on transgenic miceexpressing the APP gene from a yeast artificial chromosomecontaining genomic DNA. However, the research reported byAthena Neurosciences Inc. at the Society for Neurosciencemeeting last week involved constructing transgenic mice with acDNA version of the APP gene (see BioWorld Nov. 10).
Earlier experiments using cDNA constructs include reports inthe scientific literature by groups from the University ofCambridge in the United Kingdom, Miles Research Center andthe University of Rochester, New York.
GenPharm's Choi and Pearson introduced the human APP geneinto mouse embryonic stem (ES) cells by co-lipofection of a 650kilobase yeast artificial chromosome (YAC). This YACmethodology, in which a marker plasmid and the YAC arejointly delivered into a cell using cationic lipids, allowsresearchers to introduce very large pieces of DNA, includingentire genomic fragments, into cells.
The researchers then isolated three ES lines that contained anintact YAC and created a transgenic mouse line by germ-linetransmission of APP-expressing YACs. And those miceexpressed the human APP gene in their brains.
In these experiments, the researchers monitored transcriptionof the APP gene; they have yet to report on whether thetransgenic mice are able to produce the various isoforms of theprotein itself.
Now that the GenPharm team has demonstrated that it can getproper expression of the human APP gene in the brains ofmice, the next step is to introduce mutant forms of the APPgene into mice, MacQuitty said.
"We expect to learn a great deal about Alzheimer's disease bycomparing how mutant and normal human APP function inthese animals as they age," added Robert Kay, vice president ofresearch and development at GenPharm of Mountain View,Calif.
-- Jennifer Van Brunt Senior Editor
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