Electrical Coupling across Developmental Boundaries in Insect Epidermis

THE polarity of the surface folds on the abdominal cuticle of the insect Rhodnius which normally run at right angles to the antero-posterior axis, is controlled by the underlying epidermal cells. When portions of integument are transplanted or rotated the epidermal cells produce surface folds the orientation of which shows that the cells ``remember'', at least to some extent, their original polarity<sup>1,2</sup>. Such experiments also suggest that the cells have access to information which defines the spatial pattern of differentiation within each segment<sup>3</sup>. It has been suggested that a gradient of some property exists which is reiterated from segment to segment so that the intersegmental border intervenes between the ``high'' part of one gradient and the ``low'' of the next. In one model the segmental gradient is viewed as a concentration gradient of a diffusible morphogen^2-5. Studies in a closely related insect have shown that from a very early stage the segments have independent lineages, clones stopping abruptly at the intersegmental border^5,6.