ARTICLE

THE STRUCTURAL ORGANIZATION OF THE SEPTATE AND GAP JUNCTIONS OF HYDRA

¹ From the Laboratory of Biological Structure and The Neural Mechanisms Section, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20014

The septate junctions and gap junctions of Hydra were studied utilizing the extracellular tracers lanthanum hydroxide and ruthenium red. Analysis of the septate junction from four perspectives has shown that each septum consists of a single row of hexagons sharing common sides of 50–60 A. Each hexagon is folded into chair configuration. Two sets of projections emanate from the corners of the hexagons. One set (A projections) attaches the hexagons to the cell membranes at 80–100-A intervals, while the other set (V projections) joins some adjacent septa to each other. The septate junctions generally contain a few large interseptal spaces and a few septa which do not extend the full length of the junction. Basal to the septate junctions the cells in each layer are joined by numerous gap junctions. Gap junctions also join the muscular processes in each layer as well as those which connect the layers across the mesoglea. The gap junctions of Hydra are composed of rounded plaques 0.15–0.5 µ in diameter which contain 85-A hexagonally packed subunits. Each plaque is delimited from the surrounding intercellular space by a single 40-A band. Large numbers of these plaques are tightly packed, often lying about 20 A apart. This en plaque configuration of the gap junctions of Hydra contrasts with their sparser, more widely separated distribution in many vertebrate tissues. These studies conclude that the septate junction may possess some barrier properties and that both junctions are important in intercellular adhesion. On a morphological basis, the gap junction appears to be more suitable for intercellular coupling than the septate junction.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Facebook    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

• Leys, S. P., Nichols, S. A., Adams, E. D. M. (2009). Epithelia and integration in sponges. Integr. Comp. Biol. 49: 167-177 [Abstract] [Full Text]  
• Fraser, S., Green, C., Bode, H., Gilula, N. (1987). Selective disruption of gap junctional communication interferes with a patterning process in hydra. Science 237: 49-55 [Abstract]  
• Revel, J.-P., Nicholson, B. J., Yancey, S. B. (1982). Partial Sequence and Turnover of Rat Liver Gap Junction Protein. Cold Spring Harb Symp Quant Biol 46: 633-637 [Abstract]  

Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents