Cytotactin: a morphoregulatory molecule and a target for regulation by homeobox gene products.

Two major lines of research in developmental biology should help us to understand the bases of morphogenesis. The first is the analysis of the morphogenetic effects of local expression of various adhesion molecules. The second is the analysis of cascades of regulatory genes that interact during development. Of particular significance are regulatory interactions involving homeobox-containing genes which are expressed in a place-dependent manner in the embryo. Success in connecting these two lines of research would help to resolve the puzzle of how species-specific tissue patterns can arise and be maintained. In this article, we focus on cytotactin, a morphoregulatory molecule of the extracellular matrix that exhibits sharply restricted spatiotemporal patterns of expression during development. Recent experiments indicate the promoter of the cytotactin gene contains target regions that appear to respond to homeodomain proteins. These observations, and those on other morphoregulatory molecules, suggest a possible connection between their effects on cell patterning and control by homeobox-containing genes.