Chapter 3 Membrane Nanotubes in Urothelial Cell Line T24

Abstract Membrane nanotubes (also referred as tunnelling nanotubes—TNTs, nanotubules, cytonemes), that directly connect separated neighboring cells, may offer a very specific and effective way of intercellular transport and communication. Our experiments on T24 cell line show that TNTs can be divided into two types with respect to their biochemical and biophysical characteristics and the nature of their formation. As type I were characterized the nanotubes which are shorter, more dynamic and contain actin filaments. These structures remain stabile even if underlying actin cytoskeleton is disintegrated by cytochalasin D. The nanotubes of type II are much longer, appear more stable and contain cytokeratin filaments. In both types microtubules can be found, but this type of cytoskeleton is present in only a small fraction of the TNTs. On the nanotubes of both types small vesicular dilatations were found as an integral part of the nanotubes (i.e., dilatations of the nanotubes, gondolas). Vesicular dilatations of type I nanotubes move along the nanotubes in both directions, while the vesicular dilatations of type II nanotubes do not move along the nanotubes. Both TNTs by themselves and the transporting gondolas were proposed to be involved in intercellular communication and transport. The possible mechanisms of stabilization of membrane nanotubular protrusions and TNTs are also discussed.