Elsevier

Journal of Insect Physiology

Volume 11, Issue 2, February 1965, Pages 161-166, IN9-IN11, 167-175
Journal of Insect Physiology

Cellular membrane formation by plasmatocytes of diapausing Cecropia pupae

https://doi.org/10.1016/0022-1910(65)90102-2Get rights and content

Abstract

The early phase of wound healing in diapausing Hyalophora cecropia pupae is dominated by the formation of an acellular membrane by plasmatocytes. Phase contrast microscopic observations of blood from unwounded pupae reveal few circulating haemocytes, approximately half of which are plasmatocytes of varying morphology. In the days following injury both the absolute and relative number of plasmatocytes increase. The initial increase in cell number is not attributable to mitosis because no mitotic figures are seen until 18–24 hr after wounding, whereas substantial increases in cell number are observed by this time. A relative increase in large fusiform plasmatocytes suggests instead that the initial cellular response to injury is the release of haemocytes from depots within the insect. Subsequently, mitoses of haemocytes, particularly plasmatocytes, become rather frequent, and further increases in cell number appear to result from these mitoses.

Time lapse sequences of wound healing were photographed with phase optics through the optically flat surfaces of a plastic chamber which connected the haemocoeles of two pupae in telobiosis. As plasmatocytes touch the plastic surface of the chamber, they lose much of their heteromorphy. On these surfaces a cell typically flattens, produces a ruffled membrane, and migrates randomly over the plastic.

As the population of attached haemocytes increases, movement of the individual cells is progressively restricted. A complete cellular sheet eventually covers the plastic surfaces. This cellular membrane is subsequently thickened by the deposition of additional plasmatocytes on the blood side. The cellular membrane then degenerates and tears free from the plastic. The broken membrane fragments are pulled into the wound areas by circulatory movements of the haemolymph and partially seal the pupae from the blood chambers. Wound closure is aided by the tendency of hyaline plasmatocytes to adhere to each other and to other cells and thereby to form large clumps of cells. These clumps attach to membrane fragments and form plugs that stop the flow of haemolymph into the blood chamber.

Tracheae, accompanied by epithelial sheets, grow from the margins of the wound. The extending tracheal system aids in wound closure and is the means whereby a continuous epithelium is established across the injured area. Since hypodermal cells apparently do not undergo mitosis in the absence of ecdysone, and since only occasional hypodermal cells and a few tracheoblasts synthesize DNA in the absence of hormone, the ability of the cells of the tracheal system to migrate and produce an epithelial sheet assumes great importance for successful wound healing in diapausing pupae. Evidently the replacement of thinned-out epidermal cells as well as the secretion of a cuticle in the wound area is delayed until the hormonally mediated pupal-adult transformation.

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    This research was supproted in part by a research grant (AI-04291) from the National Institute of Allergy and Infectious Diseases, U.S. Public Health Service, and a grant from the University of Massachusetts Research Council. We thank Dr. Everett Anderson and Dr. Blair Bowers for helpful discussions and Dr. Judith Haskell for aid in preparing the figures and for reading the manuscript.

    National Institutes of Health Predoctoral Fellow (GPM-18,923) in 1962–1963.

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