Apical cell derivatives

Osteoclasts are multinucleated cells derived from pluripotent hematopoietic stem cells. Osteoclasts possess an apical membrane domain, exhibiting a ruffled border that plays a key role in bone resorption (Figure 48-12). A proton-translocating ATPase expels protons across the ruffled border into the resorption area, which is the microenvironment of low pH shown in the figure. This lowers the local pH to 4.0 or less, thus increasing the solubility of hydroxyapatite and allowing demineralization to occur. Lysosomal acid proteases are released that digest the now accessible matrix proteins. 

Encoded by the MUCI gene on chromosome I and a derivative human antigen, EMA is a transmembrane glycoprotein of the breast mucin complex, and its expression is increased in carcinomas.Unlike normal breast, in which EMA is present on the apical cell membrane, neoplasms demonstrate EMA on the entire circumference of the cell membrane. Increased amounts of the large glycoprotein interfere with cell-to-cell and cell-to-matrix adhesion in neoplastic cells. The utility of EMA antibody is in the detection of epithelial differentiation, as a supplement to the cytokera-tins. Spindle cell, small cell, and large cell neoplasms may on rare occasion be stained with EMA but may be only focally positive for cytokeratins. 437... 

Abe, S., Yamaguchi, S., Watanabe, A., Hamada, K., Amagasa, T., 2008. Hard tissue regeneration capacity of apical pulp derived cells (APDCs) from human tooth with immatme apex. Biochem. Biophys. Res. Commun. 371, 90-93. 

In the presence of Ca (Ashton, unpubl. data McClelland and Cove, unpubl. data) and R [12], spores germinate to produce primary chloronemata, i.e. filaments of primary chloronemal cells, which elongate by apical cell division. Sub-apical cells divide, usually only once or twice, to produce additional apical cells from which side-branches, composed of further branching chloronemata, are derived. Primary chloronemal apical cells divide about every 20 h (McClelland and Cove, unpubl. data) and the cross walls formed are perpendicular to the long axis of the chloronema, the cells of which contain many plump chloroplasts. 

J. Mueller, I. Born, R.H. Neubert, and M. Brandsch. Apical uptake of choline and cationic drugs in epithelial cell lines derived from human placenta. Placenta. 26 183-189 (2005). 

Figure 3.18 Schematic representation of a trilaminar cell membrane which is derived from the apical membrane of the mammary cell and forms the outer layer of the milk fat globule membrane following expression from the mammary cell, but which is more or less extensively lost on ageing. 1, phospholipid/glycolipid 2, protein 3, glycoprotein.

In spite of the fact that the driving forces remain speculative, there is now little doubt that, at secretion, lipid droplets are enveloped in apical plasma membrane, with perhaps some contribution from secretory vesicle membrane. Many questions remain, however, regarding the nature and origin of the inner coat material which lies between the triacylglycerol core and the outer bilayer membrane. To what extent is this material derived from the amorphous surface material seen on lipovesicles within the cell (Dylewski et al. 1984 Deeney et al. 1985 Keenan and Dylewski 1985) and the electron-dense coat on the cytoplasmic face of the apical plasma membrane (Franke et al. 1981) Also to be considered is the clathrin-like coat observed on the outer surface of secretory vesicles (Franke et al. 1976 Mather and Keenan 1983), which may contribute a substantial quantity of material to the lipid droplets (Franke and Keenan 1979), if secretory vesicles do indeed contribute to the formation of the milk lipid globule membrane. 

Greenwalt, D. E. and Mather, I, H. 1985. Characterization of an apically derived epithelial membrane glycoprotein from bovine milk, which is expressed in capillary endo-thelia in diverse tissues. J. Cell Biot. 100, 397-408. 

The stratum granulosum is the most superficial cell layer of the viable epidermis and contains highly differentiated keratinocytes. The lamellar bodies, which have been formed in the stratum spinosum, migrate to the apical periphery of the uppermost granular cells and eventually fuse with the membrane of the keratinocyte. Via exocytosis their content is extruded into the intercellular spaces at the stratum granulosum-stratum corneum interface. The lipids derived from the lamellar bodies are essential for the formation of the stratum corneum barrier. 

The proton pump (H+K+ATPase) of the apical membrane of the parietal cells is the ultimate mechanism that governs acid secretion. Among a family of benzimidazole derivatives, omeprazole (Losec) promotes the healing of ulcers in the stomach, duodenum, and esophagus, and is of special value in patients who do not respond to H2-receptor antagonists. 

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