The first cell fate specification event in mouse development

Abstract

The separation of inner cell mass and trophectoderm is the first cell fate specification event in mammals. The inner cell mass will form the embryo proper and contributes to extraembryonic tissues, whereas the trophectoderm will develop into the placenta to support embryo development. Two models have been proposed to describe the mechanisms behind the differentiation of these two cell types. The cell polarity model states that cell polarization followed by asymmetric cell division lies on the basis of this process. According to the inside-outside model, cell position is the ultimate determinant of cell fate. A combination of both models seems to bet explain the existing data. Early mouse development displays a high degree of developmental plasticity. A debated issue in the field is whether the differentiation between inner cell mass and trophectoderm additionally contains a component of prepatterning. In this thesis I will describe the support that exists for the different models. To illustrate the mechanisms of cell fate specification I will also describe the role of the trophectoderm specific transcription factor Cdx-2 in this process.