Biological Sciences: X Chromosome Inactivation studied by Injection of a Single Cell into the Mouse Blastocyst

Abstract

CHIMAERISM in mice, whether naturally or artificially caused, is a valuable tool in the study of development. Much information has already been gained from chimaeras made by fusing eggs at cleavage stages^1–3. Chimaeras can also be made by the injection of cells into the mouse blastocyst⁴. Because this method gives chimaerism at a later stage of development it potentially yields different information⁵, and refinement of the technique to inject a single cell into each blastocyst further enhances its scope. The injected cell divides to form a single-cell clone, which can be traced through development. In the past cloning has been used for studying X chromosome inactivation in cultured cells; we have used this new method of single cell injection for studying X inactivation in the embryo in vivo. This communication reports the birth of several mice made chimaeric by the injection of a single cell into the blastocyst, and presents preliminary results concerning the time of X chromosome inactivation in the mouse embryo.