Two studies in the mouse now suggest ways to increase the numbers of viable cloned offspring. Mice are cloned by transferring the nuclei of donor cells from adults or embryos into enucleated eggs. These eggs are then activated and implanted into foster mothers who carry the developing embryos to term. The authors injected nuclei from two genetically distinct donor strains into recipient eggs and found that they differ in their ability to generate viable offspring. This shows that some strains of animals will be easier to clone than others.
Timing is everything, particularly when it comes to activating the development of the clones.
After an egg is injected with a donor nucleus, it is treated with a chemical that triggers embryonic development. These results should help to increase the frequency of successful cloning and bring us closer to using mouse clones to unravel fundamental questions in mammalian biology. Receptor tyrosine kinases relay signals across the cell membrane, having an outer part that receives a signal, and a complex inner part that transmits the signal to different recipients inside the cell. Its function is needed for the development of blood, pigment cells and sex cells. But despite normal sexual activity once they reach puberty, the male mice are sterile.