Growth factors and pattern formation.

Growth and pattern formation occur simultaneously in many epimorphic fields and it has been suggested that specification of positional information is somehow linked to cell division. It is possible, therefore, that boundary regions responsible for the specification of positional information produce cell growth factors. In this paper I review the properties of some known growth factors, describe their effects on the cell cycle and discuss how they might act. In developing a convenient in vitro assay for morphogenetic factors it will be much easier in measure incorporation of [3H]thymidine into responding cells than to estimate changes in positional value.