[tt] Germline gene mods by tweaking sperm-producing stem cells

[Hughes, James J.]

Incidentally, the Vatican doesn't have any objection to this form of
genetic modification so long as the parents conceive through the
traditional act of monkey love. Unfortunately it only has a 10% success
rate so far.- J.

http://www.sciencedaily.com/releases/2007/09/070920145350.htm	
	
Source: 	University of Pennsylvania
Date: 	September 23, 2007

New Strategy To Create Genetically-modified Animals Developed

Science Daily - Researchers at the University of Pennsylvania School of
Veterinary Medicine have demonstrated the potential of a new strategy
for genetic modification of large animals. The method employs a harmless
gene therapy virus that transfers a genetic modification to male
reproductive cells, which is then passed naturally on to offspring.

Ina Dobrinski, associate professor and director of the Center for Animal
Transgenesis and Germ Cell Research at Penn Vet, and her colleagues
introduced adeno-associated virus, AAV, to male germline stem cells in
both goats and mice. The study showed that AAV stably transduced male
germ line stem cells and led to transgene transmission through the male
germ line.

The findings, available online in The FASEB Journal and in the February
2008 print edition, are the first report of transgenesis via germ cell
transplantation in a non-rodent species, a promising approach to germ
line genetic modification. It also demonstrates that germline
transduction and germ cell transplantation in large animals provides an
approach that is potentially less costly than microinjection and
cloning, the traditional methods used to generate transgenic large
animal models for biomedical research.

Researchers used mouse germ cells harvested from experimentally induced
cryptorchid donor testes that were then exposed in vitro to AAV vectors
carrying a green fluorescent protein transgene and transplanted to germ
cell-depleted recipient testes, resulting in colonization of the
recipient testes by transgenic donor cells.

When researchers mated these recipient males with wild-type females, 10
percent of offspring carried the gene originally introduced into the
transplanted germ cells, meaning the genetic modification had been
passed on. To broaden the approach to non-rodent species, AAV-transduced
germ cells from goats were transplanted to recipient males in which
endogenous germ cells had been depleted by fractionated testicular
irradiation. Transgenic germ cells colonized recipient testes and
produced transgenic sperm. When semen was used for in vitro
fertilization, 10 percent of embryos were transgenic.

"Initially, the team used the established germ cell transplantation
model in the mouse to investigate whether AAV-mediated transduction of
germ cells was possible and could result in transgene transmission,"
Dobrinski said. "To broaden the applicability of the results for
different mammalian species, the approach was then applied to a large
animal species in which germ cell transplantation-mediated transgenesis
would provide an important alternate approach to the generation of
transgenic animal models for biomedical research."

Currently, somatic cell nuclear transfer or pronuclear injection is used
to generate transgenic animals. These inefficient and difficult methods
also carry a risk of producing offspring with developmental
abnormalities. The use of retroviral or lentiviral vectors has been
reported in rodents, but it requires that animals be handled and
maintained under higher biosafety precautions that render this approach
less practical for transgenesis in large animal species. In contrast,
animals exposed to AAV can be maintained under standard husbandry
conditions.

AAV is a dependent virus that carries no disease and causes only a very
mild response from the immune system. Because AAV can infect both
dividing and non-dividing cells and passes its genome, it is considered
an excellent candidate for use in gene therapy.

The research was performed as a collaboration between Dobrinski, Ali
Honaramooz, Susan Megee, Jinping Luo, Hannah Galantino-Homer, Mark
Modelski, Fangping Chen and Wenxian Zeng of the Center for Animal
Transgenesis and Germ Cell Research at the New Bolton Center of the Penn
School of Veterinary Medicine; Fang Yang and P. Jeremy Yang of the
Department of Animal Biology at Penn Veterinary Medicine; Margret
Destrempes, Stephen Blash, David Melican, William Gavin, Yann Echelard
and Susan Overton of GTC Biotherapeutics Inc.; and Sandra Ayres of the
Tufts Cummings School of Veterinary Medicine.

The research was supported by a grant from the National Institute of
Child Health and Human Development and the National Center for Research
Resources.