In the span of one week, three independent research groupshave reported in scientific literature the successful introductioninto mice of very large pieces of foreign DNA -- via yeastartificial chromosomes (YAC) -- and the transmission of thattransgenic DNA through the germline.
They have used three different methods to introduce thoseYACs into the recipient cells -- spheroplast fusion, micronuclearinjection, and now lipofection -- all apparently successful. Thusthe research community now has the techniques to geneticallymanipulate pieces of DNA as large if not larger than somehuman genes (Factor VIII weighs in at a hefty 180 kilobases)and to study their functions in an in vivo transgenicbackground.
Interestingly, last Wednesday Science lifted its embargo by oneweek of a paper on "Germ Line Transmission of a YeastArtificial Chromosome Spanning the Murine Alpha 1(1)Collagen Locus," by William Strauss and his colleagues at theWhitehead Institute for Biomedical Research in Cambridge,Mass. This coincided with the publication in last Thursday'sissue of Nature of two papers on YACs, by researchers at CellGenesys Inc. of Foster City, Calif., and by a group from theGerman Cancer Research Center in Heidelberg (see BioWorld, 18March).
Strauss and his collaborators used lipofection -- transfectionvia DNA-lipid micelles -- to introduce into murine embryonicstem (ES) cells a YAC clone spanning 150 kilobases surroundingthe murine collagen locus; as well, the cloning vector containedthe sequences for the drug-resistance marker (neomycin) toallow selection of transfected cells.
From those arose two transgenic mouse strains, whichexpressed the collagen transgene at levels comparable to theendogenous collagen gene. "We see physiologic levels ofexpression of the transgene," explained Strauss. "The reasonyou want to do these experiments is to confer someappropriate trait to the animal," he told BioWorld. "We'reinterested in studying regulation and expression of genes."
The lipofection technique used by the Whitehead researchers is"very similar" to the one that GenPharm International Inc. isusing in its human YAC program, said Howard Rosen, directorof corporate development of the Mountain View, Calif.,transgenic animal company.
But Wallace's group has incorporated its marker gene into thevector itself, whereas GenPharm puts its selectable marker on aseparate YAC and then "co-lysofects." (Whitehead researcherand co-author Rudolf Jaenisch is on GenPharm's scientificadvisory board.) Rosen said the Whitehead Institute and MIT(Whitehead's parent organization) have filed a European patenton the technology.
-- Jennifer Van Brunt Senior Editor
(c) 1997 American Health Consultants. All rights reserved.