Current methods for producing genetically modified animals for scientific research can be imprecise and time-consuming, and modification of many animal species is simply not possible. A new and improved method for genetic modification, relying on a special type of cell that can be used instead of sperm to artificially fertilize an egg, has now been introduced.Jinsong Li and researchers at the Chinese Academy of Sciences (Shanghai, China) created haploid embryonic stem cells (haESCs) by removing the nucleus from egg cells and injecting them with sperm. The cells have only the genetic material of the sperm, and therefore have only one copy of each gene, but unlike sperm cells, they are able to divide and replicate. The scientists injected these cells into new egg cells, mimicking the natural fertilization process that occurs when sperm infiltrates an egg and resulting in a blastocyst consisting of cells that combine the genetic material of the egg and the haESC. The researchers confirmed that when this type of blastocyst is transferred into the uterus of a female mouse, it is able to develop into a healthy mouse (Celt 149, 605-617; 2012).
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