Epidermal feet in insect morphogenesis

Abstract

In many insects the larval cuticle pattern changes at metamorphosis to one of transverse ripples, often with a shortening of the segments (for example, Rhodnius, Hemiptera¹; Calpodes, Lepidoptera; Tenebrio, Coleoptera²). The orientation of these ripples in Rhodnius was used to discover a segmentally repeating gradient of positional information³. Since then there has been much work onthe gradient^4–6 but little on the mechanism by which an epidermal cell controls the cuticle pattern that allows us to read its orientation in the gradient. We report here that in the larval/pupal transformation of Calpodes and other insects, the epidermis develops basal cytoskeletal extensions or feet, oriented in the direction of the gradient at right angles to the ripples. Their contraction coincides with segment shortening and transverse ripple formation. Epithelial cells of the integument are not always packed together like polygonal paving stones as they are usually depicted, but may relate to one another by cytoskeletal extensions of a kind that are more usually reported from separate moving cells in tissue culture. Such epidermal feet may have general relevance in morphogenesis.