Speedy Mouse Eludes Time Trap

DOCK-A-GENE

Sarah Bronson first demonstrated Hprt docking in the mid-1990s when she was in Oliver Smithies' group at the University of North Carolina.¹ "Hprt was chosen specifically because we expected it to be neutral and permissive," says Bronson, now an assistant professor of cellular and molecular physiology at Pennsylvania State University. Several other groups have since used hprt technology, and Bronson has developed further applications.²

Bronson gave some of her reagents to Alan Peterson, associate professor of neurology at McGill University in Quebec. His group produced 17 lines of transgenic mice to study the promoter of the myelin basic protein gene.³ "But [producing the mice] was nearly as difficult as making knockout mice," Peterson says.

To speed things up, the researchers used C56BL/6 and multiple 129 strains to produce a line of vigorous ESCs. Then they removed most of the hprt locus. The resulting BPES cells (named after people in Peterson's lab) quickly colonized a wild-type blastocyst and populated the resulting mouse with their progeny. "Virtually all of the HAT-resistant clones [which contain a functioning hprt gene] contain the appropriately docked construct and, with BPES cells, most of the chimeras are dominated by the ESC lineage," Peterson says.

Because the hprt locus resides on the X chromosome, expression is the same from generation to generation, Fages says, "So we don't have to go to the F2 generation to get stable expression."

SPEEDING MOUSE DEVELOPMENT

Peterson says his group has taken "a significant number" of constructs from DNA to newborn chimeras in the course of a month. He adds, "The technology has vastly expanded the type of question [s] we can address."

"Alan certainly represents one of the groups that have made good use of the targeting strategy we developed," says Bronson. She notes also that several academic labs have good germline-competent ESC lines with the necessary hprt deletion; however, these are not available commercially.

McGill University is patenting the BPES cells and has licensed the technology to Nucleis. Another French company, ProSkelia, which analyzes the morphology, density, histology, and biochemistry of mouse bones, recently used Speedy Mouse Technology and will soon phenotype founders containing four different transgenes of interest to ProSkelia.

Michael Wiles, director of technical development at the Jackson Laboratory in Bar Harbor, Maine, says he wonders whether the Speedy Mouse's mixed genetic background will result in too much cellular noise. He also expresses skepticism of the company's timeline. "In reality, people are unlikely to use the founders themselves as their experimental animal, because using them as throwaways would seem too expensive." He adds that most labs don't have the capability to quickly and cheaply make new characterized founders from frozen transgenic ESCs.

Despite his reservations, Wiles says the technology seems "pretty good," and he adds that any technology that can produce transgenic mice more rapidly "is definitely a positive thing."

- Linda Sage