The pseudoblastema in the wound healing process of the leech <i>Hirudo medicinalis</i> L. (Hirudinea): Changes in cell junctions

Abstract

The role of the connective tissue cells and their migratory behavior have been investigated in the formation and evolution of the pseudoblastema during wound healing in the leech Hirudo medicinalis. In H. medicinalis the healing process shows first a flow of cells that effectively seal the wound and form a temporary cellular clump, the pseudoblastema, which contributes to the phagocytotic process and apparently regenerates the extracellular matrix. The migratory cells forming the pseudoblastema are connective tissue cells known as vasocentral cells, which, when in a resting state, are associated with the vasofibrous cells. During the formation and evolution of the pseudoblastema several changes affect vasocentral cell junctions. At rest, vasocentral cells do not show cell to cell junctions but they show adhering junctions in contact with the extracellular matrix. These junctions disrupt during the migratory phase. When vasocentral cells regroup in the pseudoblastema, adhering junctions are formed between them, and adhering junctions making contact with the matrix appear again. As the pseudoblastema evolves, cell to cell adhering junctions become more conspicuous and undergo other changes. During the next stage of retraction, close contacts develop between pseudoblastema cells and neighboring nondamaged muscle fibers, which probably serve as points of anchorage for the approaching movement of the wound edges. Finally, cell to cell and cell to matrix junctions disappear and the pseudoblastema disintegrates.