Apical protein complex

FIG. 2. The formation of the apical protein complex involves two distinct steps. Bazooka is localized apically in the epithelium from which neuroblasts are derived. In the interphase (G2), delaminating neuroblast formation of the apical complex is initiated. It is thought that Baz acts to allow neuroblasts to retain the apical/basal polarity inherent in the epithelium. Baz recruits Insc to the neuroblast apical stalk during delamination before Pins becomes part of the complex. During this initiation step Baz, Insc and Pins are part of a linear hierarchy. However following delamination and during mitosis, the maintenance of the apical localization of each of these proteins requires all three proteins. 

Asymmetric cell division in Drosophila neuroblasts depends on localization of the apical protein complex (Baz/ParG/ PKC3) and two sets of basal proteins. The basal proteins are incorporated into the ganglion mother cell (GMC) and contain proteins that determine cell fate (see Figure 22-24). 

Many structural components of the tight junctions (TJs) have been defined since 1992 [85-97]. Lutz and Siahaan [95] reviewed the protein structural components of the TJ. Figure 2.7 depicts the occludin protein complex that makes the water pores so restrictive. Freeze-fracture electronmicrographs of the constrictive region of the TJ show net-like arrays of strands (made partly of the cytoskeleton) circumscribing the cell, forming a division between the apical and the basolateral... 

Equilibration refers to the extent of equilibration of I2SI concentration between the apical and basal solutions. For protein complexes, the enzyme is the iodinated (125I) molecule. For glucose, the label is 3-H. 

For localized protein complexes to be differentially incorporated into two daughter cells requires that the plane of cell division be appropriately oriented. In dividing fly neuroblasts, the mitotic spindle first aligns perpendicular to the apical-basal axis and then turns 90 degrees to align with it at the same time that the basal complexes become localized to... 

Although a portion of the nutrients released from feedstuff s is absorbed by diffusing across the apical membrane of enterocytes or through the junctional complexes of adjacent enterocytes (paracellular absorption), the majority of nutrients are absorbed from the lumen of the GIT by carrier proteins that are inserted into the apical membrane of enterocytes and colonocytes. 

FIG. 1. Localization of key proteins involved in the neuroblast asymmetric cell division. During late interphase a complex of proteins including Insc, Baz (and Pins) are localized to the apical cell cortex. This complex acts to mediate the basal cortical localization of the cell fate determinants Numb (and its partner Pon), Pros (and its partner Miranda) and pros RNA (and its partner Staufen) during mitosis. During interphase, Numb is cytoplasmic and Pros is localized to the apical cortex. 

We have previously shown that a 209 amino acid region (aa288-497, asymmetric localization domain) of Insc is necessary and sufficient for apical cortical localization and for mitotic spindle orientation along the apical-basal axis (Tio et al 1999). In a yeast two-hybrid screen we identified Partner of Inscuteable (Pins), a novel 658aa protein with multiple repeats of the Tetratricopeptide (TPR) motif. Affinity purification experiments using embryonic extracts demonstrate that Pins complexes with Insc in vivo. In vitro protein interaction assays demonstrates that Pins interacts with the Insc asymmetric localization domain (see Yu et al 2000). 

From the standpoint of modeling Type I copper proteins,4,5,59,60 a variety of imidazole-based ligands containing thioether sulfurs and imidazole groups have been synthesized.61,62 The structures and spectroscopic properties of their copper(II) complexes (51)-(53) and (55)-(60) were investigated.65,79-82 To characterize apical copper(II)-thioether bonding, the complex (51) was... 

The mechanism by which Na" is reabsorbed in coupled exchange with and K+ in the collecting duct has been discussed previously that is, Na+-driven K+ secretion is partially under mineralocorticoid control. Aldosterone and other compounds with mineralocorticoid activity bind to a specific mineralocorticoid receptor in the cytoplasm of late distal tubule cells and of principal cells of the collecting ducts. This hormone-receptor complex is transported to the cell nucleus, where it induces synthesis of multiple proteins that are collectively called aldosterone-induced proteins. The precise mechanisms by which these proteins enhance Na+ transport are incompletely understood. However, the net effect is to increase Na" entry across apical cell membranes and to increase basolateral membrane Na+-K+-ATPase activity and synthesis. 

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