Transcript Document

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.