Mouse cloned from drop of blood
Tokyo: Scientists have for the first time cloned a mouse from a single drop of blood.
Researchers used circulating blood cells collected from the tail of a donor mouse to produce the clone.
The female mouse cloned from a peripheral leukocyte proved to be fertile by natural mating, and lived for a normal lifespan, researchers said.
Researchers at the RIKEN Center for Developmental Biology in Kobe, Japan, devised a technique to avoid the diminishing returns of recloning the same cell.
Success rates increased from the standard three per cent in first-generation clones to ten per cent in first-generation and 14 per cent in higher-generation clones, researchers said.
The type of somatic cell used for this process is critical and depends largely on its efficiency in producing live clones, as well as its ease of access and readiness for experimental use.
While cumulus cells, which surround oocytes in the ovarian follicle and after ovulation, are currently the preferred cell type, Drs Satoshi Kamimura, Atsuo Ogura, and colleagues questioned whether white blood cells (or leukocytes) collected from an easily accessed site, such as a tail, would be effective donor cells.
Such cells would allow for repeated sampling with minimal risk to the donor mouse.
There are five different types of white blood cells and, as expected, the researchers found that lymphocytes were the type that performed the most poorly: only 1.7 per cent of embryos developed into offspring.
The physically largest white blood cells, and thus the easiest to filter from the blood sample, were granulocytes and monocytes.
The nuclei of these cells performed better, with 2.1 per cent of the embryos surviving to term, compared to 2.7 per cent for the preferred cell type, cumulus cells.
The granulocytes' performance was poorer than expected due to a much higher rate of fragmentation in early embryos (22.6 per cent): twofold higher than that of lymphocyte cloning and fivefold higher than cumulus cell cloning.
The researchers were unable to determine what could be causing the fragmentation and intend to perform further studies to improve the performance of granulocyte donor cells.
Although the blood cells tested did not surpass the success rate of cumulus cells in this study, the researchers have demonstrated, for the first time that mice can be cloned using the nuclei of peripheral blood cells.
These cells may be used for cloning immediately after collection with minimal risk to the donor, helping to generate genetic copies of mouse strains that cannot be preserved by other assisted reproduction techniques.