Oriented fibre arrays and shape control in certain nuclei, cells and tissues

Abstract

New aspects of shape control and fibre deployment are reported for three situations: certain insect ovarian follicles, certain insect wings, and an unusual nucleus, the ciliate micronucleus. The shaping of insect follicles includes the spatio-temporal integration of intracellular and extracellular fibre arrays in the cockroach follicle. The situation is more complex than previously supposed. Similar events occur in Rhodnius prolixus follicles. It is argued, largely on the basis of my survey, that all insect follicles are involved in the control of egg shape. Evidence is also presented for follicular re-organisation and involvement as a contractile tissue during egg discharge. This possibility has never been considered before. It involves a previously undetected post-vitellogenic phase of cytoskeletal co-ordination. Epidermal cells exhibit a striking sequence of very marked changes in shape during wing morphogenesis in the dipteran insect Calliphora erythrocephala. This includes two epithelial cell contraction-elongation cycles that are spatio-temporally co-ordinated and apparently help to define the shape of a growing wing. It has been shown for Paramecium that an unusual type of spindle microtubule differentiation is involved in micronuclear mitosis. This microtubule differentiation occurs with remarkable spatial and temporal precision at specific locations within the spindle at specific stages in micronuclear elongation.