First A Spider-Goat Next a Spider-Man


My last post was on Nexia Biotechnologies tranfection of a goat with a gene to produce spider silk.  I wanted to elaborate on the technology behind the process.  A complete description is available from the company.

As a fertility specialist I know this technology well since it involves in vitro fertilization (IVF) and is the basis of what will become human gene therapy.  As they write:

The first method uses microinjection of the genetic construct into a fertilized egg. This traditional method of pronuclear microinjection involves literally injecting the genetic construct into the pronucles of a one-celled fertilized egg with an extra-fine needle. The genetic construct will merge itself with the fertilized egg’s native DNA and once this is achieved, the egg is transferred to a recipient goat and the pregnancy follows its normal course. The second method uses nuclear transfer technology. In this method, the nucleus of a cell containing the genetic construct of interest is fused to a recipient fertilized egg whose native DNA has been previously removed and the resulting egg is transferred to a recipient goat.

Ok folks- both these methods already exist in humans!  The first method is the basis of how gene therapy is planned to be done in humans.  .  This single cell is then analyzed quickly for signs of genetic diseases and I can pick the healthy embryos (without the disease) to implant into the mother’s womb.  This is called PGD or preimplantation genetic diagnosis.  The current human research is trying to refine the process (and safety) of inserting genes like was done with the goat.  Step one: fix sickle cell anemia or Tay Sach’s Disease.  Potentially eliminate it from the gene pool as well.  There are dangers however- genes for genetic diseases in some cases have potential beneficial effects that would be eliminated (like sickle cell carriers having resistance to malaria).  More ominous is potential “down-stream effects”  where changing one gene may have ripple-like effects on other seemingly unrelated genes.  Most researchers I know in this field are looking at somatic cell gene therapies (only affects the non reproductive tissues) so “problems” are not passed on to offspring as would be with germ-cell (egg and sperm affected) techniques. 

The second technique was a promising technique to deal with age related infertility.  There is a high level of egg dysfunction from the eggs of older women.  Researchers in infertility took eggs from an older woman and removed the gene-containing nuclei and used it to replace the nuclei of the egg from a young donor.  In theory, if the old egg was genetically normal but had poor supporting stuff then placing it in a young egg host would lead to increased fertility.  This technique has essentially been banned by the FDA.  I was present at a meeting of the ASRM in SAn Antonio where researchers I know with collaborators in China reported on results doing this on humans. The pregnancies did not survive.  The legal and ethical ramifications are huge and reviewed here. 


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