Ultrastructural Analysis of Puncture Wound Healing

<div><p>(A) Schematic of unwounded epidermis showing the cell monolayer, its apical cuticle lining, and basal lamina. White ovals indicate nuclei.</p> <p>(B) Schematic of recently wounded epidermis showing a plug of cell debris in the wound gap. Cells and ruptured cuticle at the wound margin are shown.</p> <p>(C–S) TEM sections of unwounded (C–F) and wounded (G–S) larvae at the times indicated after wounding. Transverse sections through each wound site are shown (C, G, J, N, and Q) along with close-ups of the boxed regions at right. c, cuticle; d, debris; e, epidermis; ec, epicuticle; m, muscle; n, epidermal nucleus; p, plug; pc, procuticle; s, scab; t, trachea</p> <p>(C) Pre-wounding. The epidermis and cuticle are intact.</p> <p>(D) Apical surface of epidermal cell showing villi (arrowhead) that secrete cuticle.</p> <p>(E) Basal surface. Arrowhead, basal lamina.</p> <p>(F) Epidermal cuticle. The epicuticle (top three layers) overlies the striated procuticle layer.</p> <p>(G) 1 h postwounding. The epidermis and cuticle are discontinuous but the gap is filled with a plug (outlined by dashed line) of cell debris. The epidermis has partially separated from the cuticle beyond the wound margin (asterisks).</p> <p>(H) The plug contains highly vesiculated cell debris.</p> <p>(I) The epidermis separating (asterisk) from overlying cuticle appears vesiculated and is presumably necrotic.</p> <p>(J) 2 h postwounding. The outer portion of the plug has melanized to form an electron-dense scab (outlined by white dashed line). The epidermis and cuticle are still discontinuous.</p> <p>(K) Debris, including a necrotic trachea, in the plug. The plug is not bounded by a membrane or basal lamina.</p> <p>(L) Portion of scab showing melanized debris and trachea.</p> <p>(M) Close-up of a lamellipodium (bracket) extending into a plug at the outer edge of another 2-h wound. Note basal lamina (arrowhead) along the lamellipodium.</p> <p>(N) 8 h postwounding. The epidermis has migrated across the gap to reestablish continuity, and has secreted new cuticle beneath the scab.</p> <p>(O) A region of epidermal cell cytoplasm near wound plug debris contains vesiculated material (outlined by dashed line) that is probably phagocytosed debris.</p> <p>(P) The newly established epidermis under the wound has a continuous basal lamina (arrowhead) and apical villi (arrow) secreting cuticle.</p> <p>(Q) 24 h postwounding. The new cuticle underlying the scab is thicker and the scab is more electron dense. Four nuclei in close apposition are in a syncytium because there are no membranes separating them.</p> <p>(R) Portion of scab and old cuticle. Note that cuticle in contact with the scab is melanized.</p> <p>(S) Cytoplasmic extension (arrowhead) engulfing debris at the basal surface of the epidermis of another 24-h wound.</p> <p>Bar, 10 μm (C, G, J, N, and Q), 0.33 μm (D and E), 0.83 μm (F), 1 μm (H, M, and P), 2 μm (I and O), 1.67 μm (K and L), 4 μm (R), 1.25 μm (S).</p>