Separation of developmental compartments by a cell type with reduced junctional permeability

Abstract

Two recent reports^1,2 have suggested that the junctional membrane of the cells located at compartment boundaries in developing insect epithelia, although permeable to inorganic ions^3,4, prevents the cell-to-cell transfer of the fluorescent tracer Lucifer yellow (LY). However, cells within a compartment are linked by junctions permeable to both inorganic ions and organic tracers^1–5. These findings imply that junctional communication is important in tissue development and that spatial selectivity may allow developmental autonomy in nearby compartments. The observation that LY was occasionally seen to pass across the segment border of the milkweed bug Oncopeltus fasciatus¹ suggested to us that the permeability of the junctions of the segment border may be locally controlled. We report here that the selectivity in the junctional channels at compartment boundaries in this insect is variable and under the control of a discrete population of border cells. The extent to which these cells reduce the rate of tracer passage across the compartment boundary relative to that within the compartment is influenced by the culture medium in which the tissue is placed.