More Sensitive Handling of Pre-implantation Eggs!
24th May 2001, New Scientist reports, on the development of a device for maturing and nurturing eggs. David Beebe & Matthew Wheeler, embryologists at the University of Illinois at Urbana-Champaign, are doing this research and development work.
The device is made of a transparent plastic (elastomer) and resembles a small glass slide and contains a network of tiny channels, each around 0.2 millimetres in depth and width. The various channels are connected to programmable syringe pumps, which can move the embryos around, and add or remove fluids. With this device gentle handling of the eggs is possible, and so is selection of the best eggs with the minimum of disturbance. Many embryos can be cultured at the same time. In time the device can be developed to handle a range of diagnostic and monitoring tests, including pre-implantation genetic diagnosis (screening would be a better word, diagnosis in the popular mind implies problems that need defining.)
Embryos need different kinds of culture fluids at different stages in their development. Currently embryos are handled with pipettes and transferred from dish to another. The begin simply as eggs and sperm are mixed in a petri dish, and are retained in dishes until the blastocyst stage when they are ready to be implanted.
Improved Survival & Advantages
This device has not been tested on human embryos.
Tests at this stage have only been with mouse embryos. In the first 48 hours required to develop a mouse embryo to the blastocyst stage using traditional dish methods no embryos survived, but using the micro channelled elastomer slide 75% of the embryos survived to blastocyst, were implanted, and produced apparently healthy pups. Also if less intrusive handling improves the survival rate of embryo's there may be less need for techniques such as cytoplasm transfer which also involves the possible transfer of mitochondrial DNA, and possible unintentional germline changes in the offspring.
A new discovery of this work concerns the removal of the "zona pellucida" (a transparent protective gel covering on the egg). Traditionally the egg was put into an acid medium and removed as soon as the break up of the shell begins. In this process it was discovered that simple washing triggered the break-up. The eggs didn't need to be left in the acid until the break up began.
Tom Shakespeare, of PEALS, in Newcastle UK said that quality control raises ethical issues. "If we are talking about maximising the chances of becoming pregnant and carrying to term, then there's less argument. But if we are talking about either reducing genetic diversity or indeed enhancing selection there are major questions."