Everything about Polly And Molly totally explained
Polly and Molly (Born 1997 - died unknown), two
ewes, were the first
mammals to have been successfully
cloned from an adult somatic
cell and to be
transgenic animals at the same time. This isn't to be confused with
Dolly the Sheep which was the first animal to be successfully cloned from an adult somatic cell where there was no genetic manipulation carried out on the adult donor nucleus. Polly and Molly, like Dolly the Sheep was cloned at the
Roslin Institute in
Edinburgh,
Scotland.
The creation of
Polly and Molly was building on the experiments of Somatic Nuclear Transfer that had led to the cloning of
Dolly the Sheep. But the crucial difference was that in creating Polly and Molly, scientists injected in their DNA a new gene. The gene chosen was of a therapeutic value to Humans to demonstrate the potential of such Recombinant DNA technology combined with Animal Cloning to produce pharmacological and therapeutic proteins to treat human diseases. The protein in question was the human blood clotting factor IX. Another difference to Dolly the Sheep was the source cell type of the nucleus that was transferred. In the case of Dolly the Sheep, the nucleus that was transferred came from mammary gland cells from a 6-year-old ewe but in the case of Polly and Molly the nucleus of Fibroblast cells were cleaned.
Background
Prior to the production of Polly and Molly, the only demonstrated way to produce a transgenic animal was by
Microinjection of DNA into the pronuclei of fertilized oocytes. However, only a small proportion of the animails will integrate the injected DNA into their genome and in the rare cases that they do integrate this new genetic information, the pattern of expression of the injected transgene's protein due to the random integration is very variable. As the aim of such research is to produce an animal that expresses a particular protein in high levels in, for example, its milk,
Microinjection is a very costly procedure that doesn't produce the desired animal.
In mice, there's an additional option for genetic transfer that isn't available in animals.
Embryonic stem cells provide a means to transfer new DNA into the
germline. They also allow precise genetic modifications by
gene targeting. Modified embryonic stem cells can be selected in vitro before the experiment moves on further for the production of an animal.
Embryonic stem cells capable of contributing to the
germline of livestock species such as sheep have not been isolated.
The production of
Dolly the Sheep and also the
Megan and Morag, the two sheep that led to the production of Dolly, demonstrated that viable sheep can be produced by
nuclear transfer from a variety of somatic cell types which have been cultured in vitro. Polly and Molly represented the further step whereby somatic cells were cultured in vitro, just as in the case with the previous sheep, but in this case they were transfected with foreign DNA, and transfected cells which stably integrated this new piece of genetic information were selected. The nuclei of these somatic cells was then transferred into an empty oocyte, as in the procedure of
nuclear transfer and this was used to produce several transgenic animals. A cell type PDFF was used. PDFF5 would produce male animals and were not transduced. Cell type PDFF2 produced female animals and were transduced. Of the gestations that occurred, 3 PDFF2 animals were born, two of which survived birth 7LL8 and 7LL12. These animals were transfected but contained a marker gene not the cloned gene of interest. These were named "Holly" and "Olly". Another subset of female producing PDFF2 cells, PDFF2-12 and PDFF2-13 also produced animals which had the cell of interest together with the marker. Of these lambs 7LL12, 7LL15 and 7LL13 were born alive and healthy. Two of these were named Polly and Molly.
Transgene
The transgene that was inserted in the donor somatic cells was designed to express human clotting
factor IX protein in the milk of sheep. This protein plays an essential role in blood coagulation and deficiency leads to the disease
Haemophilia B of which treatment requires intravenous infusion of
factor IX. The production of this protein in livestock milk, a process known as
pharming, would provide a source of this therapeutic protein that would reduce the cost and also would be free of potential infectious risk associated with the current source of this protein (human blood).
Further Information
Get more info on 'Polly And Molly'.
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