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First mammalian stem cells grown with only one set of chromosomes

12 September 2011
Appeared in BioNews 624

UK researchers have for the first time created mouse embryonic stem cells using just one set of chromosomes. Most mammalian cells, except sperm and eggs, are diploid, meaning they contain two sets of chromosomes. The ability to produce haploid cells, that contain only one set of chromosomes, may prove helpful in revealing the different functions of our genes.

'These embryonic stem cells are much simpler than normal embryonic mammalian stem cells. Any genetic change we introduce to the single set of chromosomes will have an easy-to-determine effect. This will be useful for exploring in a systematic way the signalling mechanisms within cells and how networks of genes regulate development', said Dr Anton Wutz, who led the study at the Wellcome Trust Centre for Stem Cell Research at the University of Cambridge.

Genetic studies often involve randomly mutating a gene in order to uncover its importance in a cell or organism. In simple model organisms, like bacteria and yeast, this is more easily achieved as they have haploid genomes, with only one copy of the gene to mutate. Mice and other mammals however have diploid genomes and so contain two copies of the gene 

In diploid genomes, the effects of a mutation in one copy of the gene can be masked by the second, normal copy of the gene. Introducing the same mutation in both copies of the gene involves the more complicated procedure of introducing targeted, point mutations. The creation of haploid cells therefore overcomes the need for this complex procedure.

'If you take our haploid embryonic stem cells and you introduce a mutation in a gene, you can immediately assess what the loss of gene function does to the cell', said Dr Wutz 

Researchers created the haploid stem cells by stimulating unfertilised eggs to divide. A small proportion of these cells continued to divide into multicellular, haploid embryos from which the researchers derived haploid blastocysts. The inner stem cells of the blastocysts were then extracted and continued to divide, thereby creating a population of haploid embryonic stem cells.

Dr Michael Dunn, head of molecular and physiological sciences at the Wellcome Trust, who was not involved in the study said: 'This technique will help scientists overcome some of the significant barriers that have so far made studying the functions of genes so difficult. This is often the first step towards understanding why mutations lead to disease and, ultimately, to developing new drug treatments'.

Derivation of haploid embryonic stem cells from mouse embryos
Nature |  7 September 2011
Haploid Stem Cells
The Scientist |  7 September 2011
Wutz, A., and Leeb, M. “Derivation of haploid embryonic stem cells from mouse embryos,” Nature, doi:10.1038/nature10448, 2011.
Wellcome Trust - press release |  8 September 2011
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