Conway Review Lecture 1990
10/09/1990 in Dublin
Control of Growth in Preimplantation Embryos
Dr. Michael T. Kane, Department of Physiology, University College, Galway.
I would like to thank the President and the Selection Committee of the Academy for the honour of an invitation to present the 1990 Conway Review Lecture. The subject of the topic is the Control of Growth in Preimplantation Embryos.
Introduction:
Information on the control of growth in the preimplantation mammalian embryo is of major interest both because of its relevance to human and animal fertility, and because the embryo is an extremely interesting biological entity. At the blastocyst stage it becomes capable of rapid invasive growth and in spite of the fact that it is foreign tissue it escapes rejection by the mother’s immune system – “le scandale immunologique”.
The following brief account of preimplantation development is included to set the lecture in the context of the whole area of growth control and differentiation in the preimplantation embryo.
The one-cell mammalian embryo is a relatively large cell whose size varies with the species from about 70 to 140 Ixm. The first stage of preimplantation development is called cleavage and consists of a series of cell divisions which progressively reduce cell size and the cytoplasmic nuclear ratio to that of a normal cell. This process takes place in the oviduct over a period of 2-3 days. Towards the end of the cleavage process cells start to form cell-cell junctions and compact to form a ball of cells, the morula. The next stage of embryo development is blastocyst formation. During this process the embryo first differentiates to form a layer of outer cells, the trophoectodermal or trophoblastic layer and a clump of inner cells, the inner cell mass. The trophoectodermal cells pump ions and water and generate a fluid filled cavity, the blastocoele. In species such as the mouse, blastocyst formation is quickly followed by hatching or shedding of the noncellular envelope, the zona pellucida and implantation then takes place.