George K. Ojakian

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A fundamental aspect in the morphogenesis of a polarized epithelium is the formation of structurally and functionally distinct apical and basal-lateral domains of the plasma membrane. The formation of these membrane domains involves the accumulation of domain-specific proteins and removal of incorrectly localized proteins. The mechanisms involved in these(More)
A monoclonal antibody made against a 135-kD glycoprotein (gp135) on the plasma membrane of Madin-Darby canine kidney (MDCK) cells was used to study the development and maintenance of epithelial cell surface polarity. Immunofluorescence microscopy and immunogold electron microscopy of confluent monolayers demonstrated that gp135 had a polarized cell surface(More)
The development of cell polarity in Madin-Darby canine kidney (MDCK) cells has been analyzed under conditions in which cells are induced to form multicellular epithelial cysts in stages that mimic the ontogeny of epithelial tissues and organs in vivo. The morphogenesis of MDCK cysts in suspension culture or in a collagen gel proceeds in distinct stages(More)
Treatment of the kidney epithelial cell line MDCK with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces a large increase in the permeability of tight junctions within 2-4 hr. This change in transepithelial permeability is accompanied by alterations in cell morphology that include the opening of tight junctions, loss of apical surface(More)
Rab3 proteins (isoforms A, B, C and D) are low molecular weight GTP-binding proteins proposed to be involved in regulated exocytosis. In the present study, Rab3 protein expression and localization was examined in rat parotid gland by reverse transcription (rt) PCR, Western blotting and immunocytochemistry. An approximately 200 bp PCR product was obtained(More)
In open monolayers of epithelial cells grown in vitro, the apical membrane domain forms on the free cell surface that faces the culture medium. However, in vivo, the apical lumenal compartment arises within groups of cells that do not have a free cell surface. We designed in vitro culture conditions, using small colonies of MDCK cells overlaid with(More)
Previous experiments on MDCK cells have demonstrated that the polarized appearance of a 135 kDa glycoprotein (gp135) on the apical plasma membrane can occur through the insertion of both newly synthesized gp135 as well as a pre-existing gp135 intracellular pool. In this study, anticytoskeletal drugs were utilized to determine the role of the cytoskeleton in(More)
Using monoclonal antibodies directed against the plasma membrane of Madin-Darby canine kidney (MDCK) cells, we demonstrated previously that a glycoprotein with an Mr = 23,000 (gp23) had a non-polarized cell surface distribution and was observed on both the apical and basolateral membranes (Ojakian, G. K., Romain, R. E., and Herz, R. E. (1987) Am. J.(More)
We examined epithelial cell surface polarity in subconfluent and confluent Madin-Darby canine kidney (MDCK) cells with monoclonal antibodies directed against plasma membrane glycoproteins of 35,000, 50,000, and 60,000 mol wt. The cell surface distribution of these glycoproteins was studied by immunofluorescence and immunoelectron microscopy. At the(More)
Stacked chloroplast membranes isolated from Chlamydomonas reinhardtii have differentiated particle arrays when examined by freeze-fracture electron microscopy. When the membranes are isolated unstacked, these particle arrays are lost and the fracture faces have a homogeneous appearance. The changes in appearance are due to rearrangement of existing membrane(More)