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John B Gurdon

Publications and source records attributed to John B Gurdon.

7 recordsLinked to original sources
PubMed2006

Nuclear transplantation in Xenopus.

Nuclear transplantation in amphibia started in 1952. By this is meant, sexually mature cloned frogs can be obtained from the nuclei of embryo cells, differentiating cells, and larval-differentiated cells. Transplanted nuclei are reprogrammed to entirely new patterns of gene expression. In this chapter, the methods used to transplant living nuclei into enucleated eggs of Xenopus are described. A method also is described for transplanting multiple somatic cell nuclei into nonenucleated oocytes, a procedure that achieves reprogramming of gene expression in the absence of cell division.

Active Transport, Cell Nucleus↗
PubMed2005

Epigenetic memory of active gene transcription is inherited through somatic cell nuclear transfer.

The transplantation of somatic cell nuclei to enucleated eggs has shown that genes can be reprogrammed to an embryonic pattern of expression, thereby indicating a reversal of their epigenetic state. However, in Xenopus nuclear transfer experiments using both endoderm and neuroectoderm donor cells, we have observed substantial overexpression of donor cell type-specific genes, both spatially and temporally, in the wrong cell type in some nuclear transplant embryos. For example, more than half of the embryos prepared from transplanted neuroectoderm nuclei overexpressed the neuroectodermal marker gene Sox2 to an excessive level in their endoderm cells. Because, in Xenopus, there is no transcription for the first 12 cell cycles, some somatic cell nuclei must remember a developmentally activated gene state and transmit this to their mitotic progeny in the absence of the conditions that induced that state. We also find that donor cell-specific genes are transcribed at an earlier stage than normal in an inappropriate cell type. This phenomenon of epigenetic memory applies to genes that are transcribed in donor nuclei; it does not influence those genes that are competent to be transcribed in nuclear transplant embryo tissue, but were not actually transcribed in donor nuclei at the time of nuclear transfer. We conclude that an epigenetic memory is established in differentiating somatic cells and applies to genes that are in a transcriptionally active state.

Animals↗
PubMed2003

Nuclei of adult mammalian somatic cells are directly reprogrammed to oct-4 stem cell gene expression by amphibian oocytes.

Nuclear reprogramming by the transplantation of somatic cell nuclei to eggs (in second meiotic metaphase) is always followed by a phase of chromosome replication and cell division before new gene expression is seen. To help understand the mechanism of nuclear reprogramming, we have asked whether the nuclei of normal, nontransformed, nondividing, and terminally differentiated mammalian cells can be directly reprogrammed, without DNA replication, by Xenopus oocytes. We find that nuclei of adult mouse thymocytes and of adult human blood lymphocytes, injected into Xenopus oocytes, are induced to extinguish a differentiation marker and to strongly express oct-4, the most diagnostic mammalian stem cell/pluripotency marker. In the course of 2 days at 18 degrees C, the mammalian oct-4 transcripts are spliced to mature mRNA. We conclude that normal mammalian nuclei can be directly reprogrammed by the nucleus (germinal vesicle) of amphibian oocytes to express oct-4 at a rate comparable to that of oct-4 in mouse ES cells. To our knowledge, this is the first demonstration of a stem cell marker being induced in a differentiated adult human cell nucleus. This is an early step toward the long-term aim of developing a procedure for reprogramming readily accessible human adult cells for cell replacement therapy.

Animals↗
PubMed2002

A dynamic requirement for community interactions during Xenopus myogenesis.

The community effect is an interaction among a group of many nearby cells that is necessary for them to maintain tissue-specific gene expression and differentiate co-ordinately. A community interaction is required for the muscle precursor cells of the Xenopus embryo to develop into terminally differentiated muscle, but exactly when and where the community effect acts during myogenesis has not been determined. Here, we ask whether dependence on the community effect varies with the developmental age of the muscle precursor cells. We find that dependence on the community signal changes with time through the muscle precursor cell population. During neurulation muscle precursor cells that are still in the vicinity of the blastopore and that are fated to form posterior muscle continue to require interactions with their neighbours, while differentiation of the anterior paraxial mesoderm,which gastrulated earlier, is independent of cell contact at this time. Thus the time during which a particular sub-population of muscle precursor cells requires a community interaction is related to their final destination along the anterior-posterior axis. In addition we show that this later acting community interaction around the blastopore involves FGF signalling.

Animals↗
PubMed2002

Uncommitted Xenopus blastula cells can be directed to uniform muscle gene expression by gradient interpretation and a community effect.

The animal cap cells of Xenopus blastulae behave as multi-potent stem cells in so far as they can differentiate along many unrelated pathways according to the kind and amount of signal factor that they experience. At first, animal cap cells activate early zygotic genes across a broad range of TGFbeta concentrations; soon after this, they activate later genes more intensely and over a narrow concentration range. Here we show that uncommitted blastula cells can be directed, by the sequential influence of a particular concentration of a TGFbeta morphogen and an FGF-mediated community effect, to form a homogeneous single cell type. As a result of these two signalling processes, an entire population of animal cap cells can be converted, in the absence of other signals, to a uniform population of one tissue type. Mesoderm cells that experience a particular concentration of activin increase their XMyoD expression by 10-fold and become distinct from neighbouring cells that received lower or higher concentrations of activin. The signalling processes that we employ here may be important in normal development and useful in guiding stem cell differentiation.

Activins↗