|MadSci Network: Development|
Your question was addressed directly by Barton, Surani and Norris (Nature 1984 Sep 27-Oct 3; 311(5984): 374-6) who made mouse embryos that had double copy of maternal genes or of paternal genes. Neither the paternal-only nor the maternal-only embryos developed normally. The embryos that only had maternal genes were almost normal-sized, but the extraembryonic tissue tissue (structures that nourish the embryo, such as the placenta) was underdeveloped. On the other hand, the embryos that only had paternal genes were puny, but the extraembryonic were almost normal. This was one of the groundbreaking experiments that showed parental imprinting in mammalian genome. Imprinting is a mechanism by which some genes ar preferentially silenced in males and in females. The genes that are silenced in male gametes are active in female gametes and vice-versa. Thus, dividing the genes in the embryo as “mom’s” and “dad’s”. This mechanism was first found in insects and now has been shown to happen in mammals as well, including humans. As a consequence of imprinting, the embryo needs both maternal AND paternal genomes to develop properly. Some researchers interpret parental imprinting as a difference in interest between the parents when it comes to the growth of their offspring. In species where males mate with multiple females (such as the mouse), the male would like to see the female invest as much as possible on his offspring, thus making the placenta larger. She, on the other hand, would like to produce additional offspring with other males, to ensure diversity. Therefore, it would serve her interest to ration her resources. The resulting embryo of a normal mating would be a balance of both. How is imprinting generated and how is it maintained is still a subject of intense study. Until we understand better the mechanisms that regulate imprinting, we will not be able to interfere with it. Therefore, I can’t really answer your question regarding stripping of the imprinting signals to generate viable zygotes. All I can say is, from what we know today, imprinting is a very complex mechanism that can’t be messed around with yet. I hope this was helpful. If you are interested in knowing further about imprinting, I suggest that you read “Parental Imprinting of Genes” in the October 1990 issue of Scientific American pg 52-60.
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