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Press release
The factor that controls the capacity of eggs to replicate identified at last | |||
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Paris, October 16, 2002 |
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| Researchers
at the Institut de Génétique Humaine (Institute of Human Genetics)
of the CNRS in Montpellier have just identified, in a vertebrate, Xenopus,
the factor that confers on the egg its competence to replicate its genome
after fertilization. This factor is Cdc6, a protein already known for its
role in cell proliferation. The possible implications of this work are such
that the use of Cdc6 as a fertilizability marker is the subject of a patent
application. This discovery is published in Nature of October 17,
2002. In vertebrates, meiosis is a crucial step in development because it makes it possible, in females, for immature oocytes to be transformed into eggs ready to be fertilized. Only these ova are capable of replicating their genome to give an embryo, but only after encountering a spermatozoon. As early as 1967, the hypothesis of the existence of a factor that regulates the replication competence of the DNA was advanced, and it was then confirmed in the nineteen nineties. But this is the first time that a team of researchers has succeeded in identifying it. It is known as Cdc6, a protein involved in the initial phases of DNA replication during cell proliferation. The researchers observed that the factor Cdc6 is not detectable in immature oocytes whereas it is present at the end of meiotic maturation, as well as in fertilized eggs. They have demonstrated that, in Xenopus, Cdc6 is firstly pre-stored in the immature oocyte in the form of a messenger RNA. Then, the oocyte maturing into an egg triggers the synthesis of protein, just before the egg is fertilized. By means of this mechanism, oocytes can thus remain in the ovaries for years, in the quiescent state, without any risk of them starting to replicate prior to fertilization. This work confirms the decisive role that Cdc6, and other factors of the same family, could play, when a diagnosis is to be made on the capacities of a cell to proliferate normally or pathologically. They also reveal a new molecular mechanism that provides a balance between cell proliferation and cell differentiation, both of which are essential to the embryo developing harmoniously. References: Competence to replicate in the unfertilized egg is conferred by Cdc6 during meiotic maturation, Jean-Marc Lemaître, Stéphane Bocquet, Marcel Méchali, Nature, October 17, 2002. Researcher
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