Abstract
The apical cytoplasm of epithelial cells of the small and large intestines has been examined by freeze-etch techniques as well as conventional and high voltage electron microscopy of sectioned material to gain a better understanding of the fine structural organization of the terminal web region. In the small intestine the terminal web exhibits a distinct stratification caused by the association of different sets of filaments with the three members of the junctional complex. Individual filaments of this network are closely associated with the sealing elements of the tight junctions, the surface of the core microfilament bundles, and the intermicrovillar plasma membrane. This region of the terminal web is the apical zone. The adherens zone appears as a band of interwoven filaments of two different diameters extending across the cytoplasm at the level of the intermediate junction. Within this region of the terminal web, individual 60-70 A actin-like filaments separate from the bundles of core microfilaments to interact with one another and with filaments of similar diameter from the zonula adherens. 100 A tonofilaments also contribute to the adherens zone, presumably stabilizing the orientation of the actin-like filaments. The basal zone which underlies the adherens zone consists of closely interwoven bundles of tonofilaments that are anchored to and interconnect the spot desmosomes. Within the large intestine the cytoplasmic microfilaments form a looser and less clearly stratified network which nevertheless retains the same basic organization found in the small intestine. Transmembrane linkers appear to originate within the cytoplasmic plaques of the spot desmosomes, pass through the plasma membranes, and meet in a staggered configuration in the intercellular space; these linkers may thus mediate the actual mechanical coupling between the cytoskeletal networks of tonofilament bundles of adjacent cells. This integrated system of cytoplasmic filaments and intercellular junctions endows the apical cytoplasm with both the flexibility and the stability necessary for the normal functioning of the epithelium.
Full Text
The Full Text of this article is available as a PDF (6.4 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Borysenko J. Z., Revel J. P. Experimental manipulation of desmosome structure. Am J Anat. 1973 Aug;137(4):403–421. doi: 10.1002/aja.1001370404. [DOI] [PubMed] [Google Scholar]
- FARQUHAR M. G., PALADE G. E. Junctional complexes in various epithelia. J Cell Biol. 1963 May;17:375–412. doi: 10.1083/jcb.17.2.375. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hull B. E., Staehelin L. A. Functional significance of the variations in the geometrical organization of tight junction networks. J Cell Biol. 1976 Mar;68(3):688–704. doi: 10.1083/jcb.68.3.688. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kelly D. E. Fine structure of desmosomes. , hemidesmosomes, and an adepidermal globular layer in developing newt epidermis. J Cell Biol. 1966 Jan;28(1):51–72. doi: 10.1083/jcb.28.1.51. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kelly D. E., Shienvold F. L. The desmosome: fine structural studies with freeze-fracture replication and tannic acid staining of sectioned epidermis. Cell Tissue Res. 1976 Sep 20;172(3):309–323. doi: 10.1007/BF00399514. [DOI] [PubMed] [Google Scholar]
- MILLER D., CRANE R. K. The digestive function of the epithelium of the small intestine. II. Localization of disaccharide hydrolysis in the isolated brush border portion of intestinal epithelial cells. Biochim Biophys Acta. 1961 Sep 16;52:293–298. doi: 10.1016/0006-3002(61)90678-3. [DOI] [PubMed] [Google Scholar]
- McNutt N. S., Weinstein R. S. Membrane ultrastructure at mammalian intercellular junctions. Prog Biophys Mol Biol. 1973;26:45–101. doi: 10.1016/0079-6107(73)90017-5. [DOI] [PubMed] [Google Scholar]
- Mooseker M. S., Tilney L. G. Organization of an actin filament-membrane complex. Filament polarity and membrane attachment in the microvilli of intestinal epithelial cells. J Cell Biol. 1975 Dec;67(3):725–743. doi: 10.1083/jcb.67.3.725. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mukherjee T. M., Staehelin L. A. The fine-structural organization of the brush border of intestinal epithelial cells. J Cell Sci. 1971 May;8(3):573–599. doi: 10.1242/jcs.8.3.573. [DOI] [PubMed] [Google Scholar]
- REYNOLDS E. S. The use of lead citrate at high pH as an electron-opaque stain in electron microscopy. J Cell Biol. 1963 Apr;17:208–212. doi: 10.1083/jcb.17.1.208. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Rodewald R., Newman S. B., Karnovsky M. J. Contraction of isolated brush borders from the intestinal epithelium. J Cell Biol. 1976 Sep;70(3):541–554. doi: 10.1083/jcb.70.3.541. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Shienvold F. L., Kelly D. E. The hemidesmosome: new fine structural features revealed by freeze-fracture techniques. Cell Tissue Res. 1976 Sep 20;172(3):289–307. doi: 10.1007/BF00399513. [DOI] [PubMed] [Google Scholar]
- Staehelin L. A. Structure and function of intercellular junctions. Int Rev Cytol. 1974;39:191–283. doi: 10.1016/s0074-7696(08)60940-7. [DOI] [PubMed] [Google Scholar]