Lecture34

Transgenic birds

• Various retroviral vectors have been designed to generate transgenic birds and particularly chickens (Ronfort, Legras and Verdier,1997).

• These vectors contain envelopes recognizing embryonic chicken cells.

• These vectors can be injected into newly laid eggs. At this stage, cells are still pluripotent and may participate in the generation of gametes, leading to the transfer of the transgene to progeny.

• This approach proved highly efficient. • Indeed, the embryo at this stage contains about 60

000 cells. • Only a small proportion of these cells has a chance

of being infected by the retroviral vectors. • The resulting chickens are highly mosaic at the

transgene level, leaving very little chance of transmitting their transgene to progeny.

• An alternative proved to be more efficient. Vector injections were performed at stage 16 of embryo development in the vicinity of primordial germ cells.

• These cells were preferentially infected,

• giving the animals an acceptable chance of transmitting their transgene to progeny

• Retroviral vectors have also been implemented to transfer genes into birds.

• The viral particles were injected between the zona pellucida and the oocyte membrane at a time when the nuclear membrane was absent, giving the viral genome the best possible chance of reaching the host genome.

• Two methods have succeeded in producing chickens carrying and expressing foreign genes.

• Infecting embryos with a viral vector carrying – the human gene for a therapeutic protein – promoter sequences that will respond to the

signals for making proteins (e.g. lysozyme) in egg white.

• Transforming rooster sperm with a human gene and the appropriate promoters and checking for any transgenic offspring.

• Preliminary results from both methods indicate that it may be possible for chickens to produce as much as 0.1 g of human protein in each egg that they lay.

• Not only should this cost less than producing therapeutic proteins in culture vessels, but chickens will probably add the correct sugars to glycosylated proteins — something that E. coli cannot do.