Mechanics of the Cytoskeleton

Abstract

This chapter summarizes evidence for a cytoskeletal function intensegral integration on both the organismal and the cellular levels.The plant cytoskeleton consists of two major elements, microtubules andactin filaments. The spatial organization of these elements is highlydynamic and changes fundamentally during the cell cycle, withconspicuous effects on the predicted stress strain patterns. Ininterphase cells, microtubule bundles are thought to control thedirection of cellulose deposition and thus to reinforce the axiality ofcell growth. By microtubule-actin linkers such as the novel class ofplant-specific kinesins with a calponin-homology domain, the rigidmicrotubules and the flexible actin bundles can be integrated into asystem endowed with mechanical tensegrity. Because the plantcytoskeleton is relieved of the load-bearing task it fulfils in thenon-walled animal cells, it has adopted sensory functions.Stretch-induced changes of protein conformation and stretch-activatedion channels seem to act in concert with the cytoskeleton, which actseither as a stress-focussing susceptor of mechanical force uponmechanosensitive ion channels or as a primary sensor that transducesmechanical force into differential growth of microtubule plus ends. Thiscytoskeletal tensegrity sensor is used both to integrate the growth ofindividual cells with mechanical load of tissues and organs and as anintracellular sensor used to control holistic properties of a cell suchas organelle positioning. The distinct nonlinearity of microtubules inparticular renders them an ideal tool for self-organization in responseto mechanical input from the exterior.