This lecture starts with an introduction about the different types of electron microscopy: scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning TEM (STEM) used in biology and materials science. A brief overview will be given about the standard ways to obtain information about membrane proteins using electron microscopy, including three-dimensional TEM. The main part of the lecture will be about liquid-phase electron microscopy. TEM has traditionally been associated with the study of thin solid samples in vacuum. With the availability of reliable thin membranes of silicon nitride, TEM of liquid specimens has become accessible with nanoscale resolution in the past decade [1]. The usage of scanning transmission electron microscopy (STEM) presents a novel concept to study membrane proteins within whole mammalian cells in their native liquid environment [2]. The cells in liquid are placed in a microfluidic chamber enclosing the sample in the vacuum of the electron microscope, and are then imaged with STEM. It is not always necessary to enclose the cells in the microfluidic chamber. For many studies, it is sufficient to obtain information from the thin outer regions of the cells, and those can be imaged with high resolution using environmental scanning electron microscopy (ESEM) with STEM detector [3]. Liquid STEM was used to explore the formation of HER2 homodimers at the single-molecule level in intact SKBR3 breast cancer cells in liquid state [4]. HER2 is a membrane protein and plays an important role in breast cancer aggressiveness and progression. Within scope of the SFB1027, liquid STEM is used for research on the stoichiometry of ORAI calcium channels within the intact plasma membranes of whole cells [5].

References:

[1] de Jonge, N., Ross, F.M., Electron microscopy of specimens in liquid, Nature Nanotechnology 6, 695-704, 2011.

[2] de Jonge, N., Peckys, D.B., Kremers, G.J., Piston, D.W., Electron microscopy of whole cells in liquid with nanometer resolution, Proc Natl Acad Sci 106, 2159-2164, 2009.

[3] Peckys, D.B., Baudoin, J.P., Eder, M., Werner, U., de Jonge, N., Epidermal growth factor receptor subunit locations determined in hydrated cells with environmental scanning electron microscopy, Scientific reports 3, 2626: 1-6, 2013.

[4] Peckys, D.B., Korf, U., de Jonge, N., Local variations of HER2 dimerization in breast cancer cells discovered by correlative fluorescence and liquid electron microscopy, Science Advances 1, e1500165, 2015.

[5] Peckys, D.B., Alansary, D., Niemeyer, B.A., de Jonge, N., Visualizing quantum dot labeled ORAI1 proteins in intact cells via correlative light- and electron microscopy, Microsc Microanal 22, 902-912, 2016.