Actomyosin cortex

So far, it is not fully understood how the asymmetric PAR protein distribution is connected with the reorganization of the actomyosin cortex. Here, we have analyzed the polarity protein PAR-2 and a component of the actomyosin cortex, the non-muscle myosin NMY-2, in vivo with standard and scanning FCS inside the C3ffosol and on the cortex of C. elegans embryos. 

Imaging of the labeled embryos displayed the known distribution of the polarity involved protein PAR-2 and the actomyosin cortex protein NMY-2 during different stages of development. FCS measurements in the cytoplasm yielded autocorrelation curves for GFP PAR-2 with a diffusive or subdiffu-sive behavior. The diffusion coefficient for NMY-2 GFP is smaller, indicating much slower diffusion. The autocorrelation functions of NMY-2 GFP exhibit a sharp decay of the autocorrelation function, suggesting contributions of directed flow. Comparison of the diffusion coefficient of PAR-2 and NMY-2 with a reference protein of similar size in the cytoplasm indicates that both proteins are part of a larger complex or multimerize (data not shown). 

PAR-2 seems to be uncoupled from movement of NMY-2, a member of the actomyosin cortex, as observed in sFCS measurements on the cortex. Further investigations into the different cortical elements and polarity proteins are necessary to elude the mechanisms of asymmetric cell division in developing C. elegans embryos. FCS and sFCS are two techniques capable of investigating the dynamics of the involved proteins, providing a complementary approach to existing techniques. 

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