John Gurdon Kt DPhil DSc FRS, Distinguished Group Leader in the Wellcome Trust/CRUK Gurdon Institute in Cambridge.
Reprogramming of gene expression by nuclear transfer
The differentiated state of adult cells is remarkably stable, and ensures the normal function of our body tissues and organs. Hardly ever does a cell of one kind change into a different kind of cell. However, there are certain experimental procedures by which gene expression of a specialised adult cell can be reversed to that of an embryonic cell. This opens the way to provide therapeutically useful replacement cells of any kind from other readily available cells of another kind, such as skin.
One procedure for reversing the differentiated state of a cell is by transplanting its nucleus (frog or mammal) to an egg or oocyte. Our aim is to understand how eggs or oocytes achieve this, so as to identify the reprogramming molecules involved, and thus, eventually, to improve the efficiency of this route towards cell replacement without immunosuppression.
We use the growing eggs ('oocytes') of amphibia to activate embryo-expressing genes in the transplanted nuclei of adult mammalian cells. We have recently identified polymerised actin and its cofactors as a significant component of this oocyte transcriptional apparatus for reprogramming somatic nuclei. A question of at least as much importance is how the differentiated state of a cell makes its nucleus resistant to the reprogramming activities of an oocyte. Genes that become transcriptionally repressed in normal development are of this kind. Some genes show an epigenetic memory of their active state. We have identified macroH2A as one chromatin protein that helps to confer an inactive state of genes on the inactive X chromosome of female mammals. We have recently developed a procedure by which chromosomal proteins can be progressively removed from somatic cell nuclei to improve embryonic gene reactivation. This can lead to the identification of chromosomal components that resist reprogramming by oocytes. The removal of these could greatly improve the efficiency of nuclear reprogramming.
• Gurdon JB (2006) From nuclear transfer to nuclear reprogramming: the reversal of cell differentiation. Ann Rev Cell Dev Biol 22, 1-22. PMID: 16704337
• Jullien J, Halley-Stott RP, Miyamoto K, Pasque V and Gurdon JB (2011) Mechanisms of nuclear reprogramming by eggs and oocytes: a deterministic process?Nature Reviews Molecular, 12, 453-459
• Pasque V, Jullien J, Miyamoto K, Halley-Stott RP and Gurdon JB (2011) Genetic and epigenetic factors affecting nuclear reprogramming efficiency. Trends in Genetics, 27(12)516-525
• Narbonne P, Miyamoto K and Gurdon JB (2012) Reprogramming and development in nuclear transfer embryos and in interspecific systems. Current Opinion in Genetics & Development, 22:450-458
• Jullien J, Astrand C, Szenker E, Garrett N, Almouzni G and Gurdon JB (2012) HIRA dependent H3.3 deposition is required for transcriptional reprogramming following nuclear transfer to Xenopus oocytes. Epigenetics and Chromatin, 5:17