Apical cortical localization

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). 

However, in interphase delaminating neuroblasts, which are known to have completed S-phase and are at the G2 stage of the cell cycle, this codependence of Baz/Insc/Pins seen in mitotic neuroblasts does not apply. Delaminating neuroblasts possess an apical membrane stalk which retains contact with the epithelial surface and this is where apical cortical localization of Insc is initially seen (see Fig. 2). This initial localization of Insc to the apical stalk occurs... 

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. 

PC has two principal layers of pyramidal neurons, layers II and III, corresponding to superficial and deep pyramidal cells (Fig. 26). A third morphologically distinct subtype, the middle pyramidal cell has also been suggested, but is supported by only limited evidence (Martinez et al. 1987). Pyramidal neurons have several characteristic features and are similar to those in other cortical regions and the hippocampus (1) A primary apical dendritic trunk that extends radially towards the pial surface and arborizes into numerous smaller branches that ramify in layer la and Ib (Haberly, 1983 Martinez et al. 1987). Some of these branches turn and run parallel to the pial surface for short distances. (2) A large number of relatively thin secondary or basal dendrites that emerge from the soma and extend several hundred microns into deeper parts of PC. Both the apical and basal dendritic tree are heavily invested with spines and varicosities. (3) A myelinated axon that typically extends deep to the soma terminates on other local pyramidal cells and interneurons (see below). ... 

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