Troponin-I localizes selected apico-basal cell polarity signals

Abstract

Beyond its well characterized role in muscle contraction, Drosophila Troponin I (TnI) is expressed in other cell types where it plays a role in proliferation control. TnI traffics between the nucleus and the cytoplasm through a sumoylation-dependent mechanism.We address here the role of TnI in the cytoplasm. TnI accumulates in the apical region of epidermal cells and neuroblasts. TnI helps to localize and co-immunoprecipitates with Par-3/Bazooka and with disc large (Dlg), two components of the apico-basal polarity system. By contrast, Scribbled is not affected by TnI depletion. In neuroblasts, TnI is required for the polar localization of Miranda while non-polar Dlg is not affected. TnI loss-of-function triggers genome instability, cell apoptosis and extrusion from wing disc epithelia. However, rescue from apoptosis by p35 does not prevent genome instability demonstrating that both features, apoptosis and genome instability, are mechanistically independent. While PI3K is known to contribute to apico-basal polarity of epithelia in vertebrates, Drosophila PI3K depletion alters neither the apical localization of TnI or Par3/Bazooka, nor the basal localization of Dlg. However, the overexpression of PI3K prevents the polarity defects caused by TnI depletion. Thus, TnI binds certain apico-basal polarity signals in a cell type dependent context, and it unveils a h i t h e r t o unsuspected diversity of mechanisms to allocate cell polarity factors. 3

Cytonemes in Tumourigenesis

“…In addition, TMs in human cells provide functional coordination to GB cells and facilitate cell repair, brain infiltration, and offer resistance to radiotherapy through dilution of Ca intracellular peaks , which thereby increases the aggressiveness of GB. [16] +2 [14]…”