Dynamic Phase Microscopy Reveals Periodic Oscillations of Endoplasmic Reticulum during Network Formation

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T. V. Vyshenskaya^1,2, V. P. Tychinsky^2,3, D. G. Weiss², and S. A. Kuznetsov^1,2*

¹Faculty of Physics and Faculty of Biology, Lomonosov Moscow State University, 119899 Moscow, Russia

²Institute of Biological Sciences, University of Rostock, 18059 Rostock, Germany; fax: +49-381-498-6302; E-mail: sergei.kuznetsov@uni-rostock.de

³Faculty of Optoelectronics, Moscow State Institute for Radioengineering, Electronics and Automation, 117454 Moscow, Russia

^* To whom correspondence should be addressed.

Received April 11, 2014; Revision received May 26, 2014

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Dynamic phase microscopy was used to study the dynamic events of formation of the endoplasmic reticulum (ER) in interphase-arrested Xenopus egg extract. We have shown that the ER periodically oscillated in an ATP-dependent manner in the frequency range of 1.6-2.2 Hz, while the tubular membrane network formed in vitro. The spectral density, i.e. the pattern of a given frequency component in the Fourier spectrum, was strongly correlated with the dynamic events during microtubule-dependent and microtubule-independent ER network formation observed by video-enhanced contrast differential interference contrast and fluorescence microscopy. Because the 1.6-2.2 Hz frequency of oscillation during the network formation was detected both in the presence and absence of microtubules, it appears to be an intrinsic ATP-dependent ER membrane property. Several characteristic active and inactive stages of ER network formation were observed both in the presence and absence of microtubules. However, data analysis of these stages indicated that microtubules and dynein motor activity have a strong influence and a cooperative effect on the kinetics of ER formation by controlled fusion reaction.

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KEY WORDS: endoplasmic reticulum, membrane fusion, membrane oscillations, microtubules, dynein, Xenopus, coherent microscopy

DOI: 10.1134/S0006297914090077

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