PIP3 Waves and PTEN Dynamics in the Emergence of Cell Polarity

Abstract

In a motile eukaryotic cell, front protrusion and tail retraction are superimposed on each other. To single out mechanisms that result in front to tail or in tail to front transition, we separated the two processes in time using cells that oscillate between a full front and a full tail state. State transitions were visualized by total internal reflection fluorescence microscopy using as a front marker PIP3 (phosphatidylinositol [3,4,5] tris-phosphate), and as a tail marker the tumor-suppressor PTEN (phosphatase tensin homolog) that degrades PIP3. Negative fluctuations in the PTEN layer of the membrane gated a local increase in PIP3. In a subset of areas lacking PTEN (PTEN holes), PIP3 was amplified until a propagated wave was initiated. Wave propagation implies that a PIP3 signal is transmitted by a self-sustained process, such that the temporal and spatial profiles of the signal are maintained during passage of the wave across the entire expanse of the cell membrane. Actin clusters were remodeled into a ring along the perimeter of the expanding PIP3 wave. The reverse transition of PIP3 to PTEN was linked to the previous site of wave initiation: where PIP3 decayed first, the entry of PTEN was primed.

Actin and PIP3 waves in giant cells reveal the inherent length scale of an excited state

“…1). The average velocity of 0.11 mm6s 21 for the propagation of PIP3 bands in electrofused cells is similar to that in normal-sized cells, where an average of 0.14 mm6s 21 was found (Gerisch et al, 2012). In the cell shown in Fig.…”

“…We produced these cells by electric-pulse-induced cell fusion or by myosin II knockout in order to investigate pattern dynamics not limited by the narrow borders of normal-sized cells, which have been studied previously (Gerisch et al, 2012). As with the wave patterns in normal cells, those in giant cells are generated spontaneously.…”

“…Correlated with differences in the membrane are differences in the structure and composition of the underlying actin networkthe inner territory of densely packed actin filaments is enriched in the Arp2/3 complex, whereas the external area consists of widemeshed actin bundles that are associated with myosin-II and the actin-bundling protein cortexillin . Thus, the wave patterns on the substrate-attached cell surface provide an opportunity to image, within one plane of focus, transitions between two states of the cell membrane in line with changes in the underlying actin cortex (Gerisch et al, 2012).…”

“…The wave dynamics in Dictyostelium provide a system to study the propagation of an excited state within a single cell (Gerisch et al, 2012). The wave patterns that have been previously analyzed were formed within the boundaries of a single cell where the lateral borders confined the space for wave expansion to 10-20 mm, allowing only sections of the pattern to develop.…”

Phase geometries of two-dimensional excitable waves govern self-organized morphodynamics of amoeboid cells

“…S2D). A recent study (24) suggested PTEN depletion proceeds a few seconds ahead of PIP3 accumulation. These events appear almost simultaneously in the time resolution (10-s interval) of the present analysis.…”