Talk:Keith Campbell (biologist)
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[edit] Hybrid Embryos
Hybrid Embryos:
1. What are they? 2. Why do we need them? 3. How do we make them?
1. What are they?
Regardless of the many rumours that have been circulated suggesting that a hybrid embryo may develop which contains both animal and human characteristics this is definitely not the definition of HYBRID EMBRYOS that was the subject of the recent parliamentary and public debate.
In my opinion the term HYBRID EMBRYO is itself misleading and the term CYBRID may be more applicable. Normal embryo development consists of the combination of maternal and paternal DNA within the fertilised egg to form a functional diploid genome. The fertilised egg is a comparatively large cell and during early development the majority of components required are present in the egg. This includes proteins, messenger RNAs, mitochondria, membranes etc. Early development does not involve cell growth and the cells become smaller with each division. At the cellular level he major major event occurring is nuclear DNA synthesis in order to transfer a replicated diploid genome to each of the cells. Only later in development (e.g. 1-2 cells in mice, 4-8 in humans and pigs, 8-16 in cattle and sheep does the nuclear genome begin to direct development and produce the majority of the factors required for cellular growth subsequent development.
In somatic cell nuclear transfer (SCNT) otherwise known as ‘CLONING’, the process which was used to produce ‘DOLLY’ the sheep (2006). The maternal genome is removed from the egg and replaced with a diploid genome from another cell already containing a diploid genome as described. Cells can be removed for SCNT from embryos through all developmental stages to the adult animals, these are generally termed somatic cells (although as yet not all cell types have proved successful). In addition to controlling early development the egg components are able to ‘REPROGRAM’ the somatic genome to control development (rather like translating text into another language) the DNA code itself remains unchanged. Many experiments have suggested that many of the mechanisms allowing this translation are conserved across species and therefore for instance a sheep egg may be able to support replication of a human genome and translate the genome during early development. The translated genome would then take over and specify the nature of the proteins etc required for further development.
With time, the animal contribution from the donor egg would be slowly diluted from the resultant embryos/cell produced. There is one known exception to this, the MITOCHONDRIA. The mitochondria egg are organelles which contain DNA and control oxidative phosphorylation which provides the energy for cellular functions. Mitochondria are inherited maternally in the egg and replicate independently of the nucleus. Therefore a hybrid embryo would contain animal mitochondria. Mitochondrial function relies on nuclear factors if these were not compatible then the energy balance of the hybrid embryo/cell would be compromised and probably result in impaired function and possibly death. Using techniques developed at Nottingham in collaboration with J St. John (Warwick) it is possible that we may be able to change the mitochondria to human derived in the hybrid embryos.
2. Why do we need them?
There are a number of reasons why we should be allowed to produce hybrid embryos, these include but are not limited to;
1. To understand cellular function – for basic research. In particular to produce embryonic stem (ES) cell lines from individuals with genetic disorders/progressive diseases for which there are no cellular or animal models at the present time. 2. To produce potentially autologous (personalised) ES cells for human therapies (these would hopefully not be rejected by the bodies immune system). 3. The quality and quantity of human oocytes/eggs, which are available for research is the major limiting factor in the production of ES cells by SCNT. The use of animal eggs would, if successful, provide a huge resource for research.
4. How do we make them?
To date there are reports of human/animal and other interspecies embryos produced by SCNT spanning at least the last 10 years. The publication of the derivation of ES like cells from rabbit/human embryos is the most successful report. Other studies transferring pig/rat/primate nuclei into pig /sheep/cattle oocytes have proved less successful. AT THE VERY LEAST THESE EXPERIMENTS SHOULD BE ALLOWED TO VALIDATE THESE PREVIOUS REPORTS.
To produce these ‘hybrid’ embryos a human nucleus would be transferred into an animal egg from which the nuclear DNA had been removed. The embryo would then be cultured in the laboratory to the blastocyst stage – 5 days in humans – and then cultured so as to allow the isolation of ES cells. —Preceding unsigned comment added by Sheepman425756 (talk • contribs) 14:13, 9 June 2008 (UTC)
