Recent studies of early development in a number of ivertebrate and vertebrate species have suggested that growth factors and their receptors may play important roles in differentiation as well as cell proliferation. In the mouse embryo, the expression of the receptors for insulin and insulin‐like growth factors I and II (IGF‐I and ‐II) are temporally regulated. The ontogeny of receptor and ligand expression within the insulin and IGF gene family suggests that the very earliest stages of mammalian embryogenesis may be (...) subject to regulation by autocrine and paracrine factors from maternal and embryonic sources. (shrink)