A fertilized egg contains two copies of every gene, one from sperm and one the original egg cell — mother and father make equal genetic contributions. Usually, both copies are expressed in relevant embryo cells. But some genes are specifically 'imprinted' so that only the maternal or paternal copy is active — mother and father make unequal 'epigenetic' contributions. Now biologists have learnt more about this mysterious asymmetry from human cells with no maternal imprinting at all.
Fertilized mutant eggs died soon after implanting into the uterus wall, David T. Bonthron and colleagues at St James’s University Hospital, University of Leeds, UK, found (Nature, Vol. 416, No. 6880, 04 Apr 02). Further investigations of these cells should shed some much-needed light on how imprinting works, why it is necessary and why it sometimes fails.
In a News and Views article about this and closely related recent work, M. A. Surani of the Institute of Cancer and Developmental Biology, Cambridge, UK, concludes that "for the time being men are indispensable". "Even the relatively few epigenetic marks that have survived in the paternal genome are crucial for development and hence a significant barrier to virgin birth," he jokes, "but with the increasing pace of research, even this barrier might be breached in the future."
David T. Bonthron
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