The birth of a mouse in a petri dish -the end result of the use of an effective technique to manipulate oocytes -heralds a new era in reproductive biology
THIS mouse, was born in the Jackson laboratory at Bar Harbor, Maine, us. Its birth marked the culmination of years of research by developmental biologist
John Eppig and his research assistant Marilyn O'Brien. The actual process of raising the creature took three weeks, which is the normal period of gestation that a mouse undergoes ( Science, Vol 271, No 5249).
Any mammalian female is born with thousands of oocytes (a reproductive cell in the ovary that gives rise to an ovum) which produce eggs over a period of time. This limits the chances of successful in vitro fertilisation (IVF) which can be carried out only on mature eggs. Oocytes are surrounded by granulosa cells -white blood cells hav- ing granules in the cytoplasm -and it is believed that some kind ofbiochemi- cal signals are transmitted between the two types of cells and that it is this com- munication which acts as a prelude to the oocytes maturing into fertilisable eggs. This is what Eppig wanted to investigate when he transferred the oocyte-granulosa complex from mice into a culture dish. The first attempt failed because the granulosa cells sepa- r~ted from the complex and got stuck to the sides of the dish.
After years of playing around with conditions in the culture dish, Eppig and O'Brien finally hit upon the right conditions for developing the oocyte. First, cultures of the new-born mouse's ovaries were made before isolating the oocyte-granulosa complex. This allowed time for the granulosa cells to stick to each other in layers, rather than to the dish. The complex was then bathed with growth factors and stirnula- tory hormones, resulting in mature eggs after two weeks.
Prompted by their success Eppig and O'Brien decided to try out IVF. Forty per cent of the oocytes developed in the above manner, actually underwent fer- tilisation and cleavaged into the two-cell embryo stage. Of the 190 two-cell embryos~ that were transferred to the oviducts of surrogate mothers, onlyone managed to survive.
According to Joanne Fortune, a reproductive physiologist at Cornell University's College of Veterinary Medicine in the USA, the success rate may have been very low, but the fact that one mouse was born, was enough to render the technique feasible. This technique holds great potential for other areas like wildlife conservation and in solving problems concerned with human fertility.
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