Sperm entry point and embryo development

A group of UK researchers has discovered that the entry point of a sperm as it fertilises a mouse egg determines the orientation of the resulting embryo. Their findings, published in Nature, could have implications for a technique used to treat male infertility, in which doctors create IVF embryos by injecting a single sperm into an egg.

Previously, it was not known how a mammalian embryo 'knows' which way up it is when it begins to develop. But Magdelena Zernicka-Goetz and Karolina Piotrowska, of the Wellcome/CRC Institute in Cambridge, found that the sperm entry point dictates position of the first cell division. This in turn could determine the head-to-tail and front-to-back axes of the growing mouse embryo. Dr Alan Handyside, of the University of Leeds, points out that mouse and human embryos are very similar at this early stage. 'These findings could have direct implications for our understanding of human embryology' he told the Lancet.

Commenting on the Nature article, Dr Roger Pederson of the University of California in San Francisco writes that injecting sperm directly into human eggs during a treatment for infertility (intracytoplasmic sperm injection, or ICSI) could define embryo orientation or possibly even the future body pattern of the child. Because of this possibility, he concludes it is 'urgent' to find out how sperm affect mouse embryo development.