Cytoskeletal coordination and intercellular signalling during metazoan embryogenesis.

This article draws attention to certain recently discovered features of cell surface organization and cytoskeletal deployment that may be revealing a new basis for intercellular signalling during metazoan embryogenesis. It is a signal mode that could coordinate many aspects of 'Entwicklungsmechanik' by spatiotemporal integration of the cytoskeletal/motor network throughout developing tissues. Evidence that this is achieved by 'intercellular cytoskeletal/plasma membrane connecting systems' which coordinate the spinal organization of microtubules, microfilaments, and intermediate filaments in developing animal tissues is critically examined. It is argued that this system does operate but that it is not used to transmit positional information in embryonic fields. However, it probably responds to such information and might play an important part in establishing field boundaries during the very earliest stages of embryogenesis. Certain aspects of cell surface organization in contemporary protozoans reveal ways in which the Protozoa could have been pre-adapted for the employment of cytoskeletal/cell surface signalling during the advent of multicellularity. In marked contrast, such signalling does not appear to be exploited during plant morphogenesis. The extent to which cytoskeletal organization might be coordinated in sister cells by transmission of spatial instructions during cell division in both animal and plant tissues is also considered.