Date of Award
Doctor of Philosophy
The regulation of gap junction permeability may be important during development, since this could change the nature and rate of movement of molecules passing between cells. Results in developing insect epidermis show that intercellular channels close in a graded fashion, altering the kind of substances passing between cells over time, and that reduced junctional permeability at the intersegmental border establishes spatial patterns of coupling within the epidermis.;The nature of channel closure, which might be graded or all-or-none, determines how junctional permeability changes when the coupling level is varied. The passage of small fluorescent dyes and inorganic ions between cells was examined during gradual uncoupling by Li of epidermis from the beetle Tenebrio molitor. The junctional resistance increases monotonically over 60 minutes, but the intercellular passage of the fluorescent tracers carboxyfluorescein (CF) and lissamine rhodamine B (LRB) is blocked long before electrical coupling is lost. There is discrimination by size, since LRB, with a limiting dimension for channel passage of 14A, is blocked before CF (12A). This suggests that intermediate levels of coupling are selective, and indicates that the average channel diameter decreases during uncoupling.;The cells in adjacent segments develop largely independently of each other, under the control of separate morphogenetic gradients, but the epidermis is continuous and there is cooperation in cuticle synthesis. Regulation of intercellular communication at the intersegmental boundary may be responsible, since in the bug Oncopeltus fasciatus, LRB, CF and Lucifer yellow move freely between cells within the segment but are impeded from passage to the adjacent segment. A strip of cells at the segment border has reduced junctional permeability, which is modulated independently of that within the segment. Under conditions that block the passage of dye, electrical coupling between segments remains strong, although an increase in junctional resistance of the border cells can be detected. Exposure to the molting hormone 20-hydroxyecdysone removes the barrier to intersegmental dye spread. This suggests that while depressed junctional coupling normally limits segmental interaction, developmental regulation ensures full cooperation at critical times.
Blennerhassett, Michael George, "Selectivity In Junctional Communication" (1984). Digitized Theses. 1403.