Endocrinization of the early embryo: an emerging role for hormones and hormone-like factors

In the last decade, we witnessed the extension of endocrinologically based concepts and molecules to many other arenas of intercellular communication, e.g. immunology, hematology and cancer biology. At the start of the new decade we are witnessing the beginning of a similar transformation in our understanding of early embryogenesis, i.e. that hormones, growth factors and other hormone-like agents and their receptors, familiar to us in other contexts, may be the long-sought mediators of many key events in early embryogenesis. Why these agents were overlooked before and how they have started to emerge is the theme of this essay. The title 'Endocrinization of the Early Embryo' refers to both the biological and intellectual developments.