Although the very first electron microscopy (EM) images of eukaryotic cells were attributed in 1945, it was the Ruska family that not only developed the EM, but also pioneered in the field of infections with pictures of bacteria and viruses. It took until 1949 until the cell’s internal structures were first shown when samples for the first time were embedded in plastic to enable thin sections.

In early studies the focus was set on cellular organelles. Mitochondria and endoplasmic reticulum were the first organelles to be described in greater detail. Brain tissue observations on a cellular structure were also started as a transmission electron microscopy (TEM) project. During the times of intense research using TEM, scanning electron microscopy (SEM) was only just beginning to appear as a tool for imaging surface topography, until it was brought to light in the 1960s and 1970s [1]. This blog should offer you some insights into recent projects involving SEM in cell biological applications.

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How SEM helped observe the impact of the Golgi matrix protein giantin on the cilia function in zebrafish

A nice example was shown by Bergen et al. [2]. The Golgi matrix protein giantin was used in their study to observe its impact on cilia function in zebrafish. Imaging the olfactory pit neuroepithelial cilia with SEM, they were able to prove a difference between their control group versus two morphants.

To be able to image the cilia with a secondary electron detector, they had to fixate the samples with paraformaldehyde, dehydrate them, critical point dry them and finally sputter coat them.

From the images, they could see that the phenotype reproduced in vivo and transfected with short interfering DNA lead to bulbous cilia tips compared to smooth cilia in the knockdown cells. They could therefore show that the largest Golgi matrix protein, giantin, plays a role in ciliogenesis and the control of ciliary length.


How SEM helped observe the functional consequences for human macrophages after a treatment with carbon nanotubes

Another example extends into a human application. Sweeney et al. [3] observed the functional consequences for human macrophages after a treatment with carbon nanotubes. Aveolar macrophages provide the first line of immune cellular defense by removing foreign matter (microbes or particles) from the aveolar space.

Before being able to image the macrophages in the SEM, the cells were dehydrated with ethanol, and after that, sealed to a stub before being sputter coated. The SEM images were able to prove that untreated macrophages appeared spherical with few filopodia and just some membrane ruffling, while treated macrophages became activated, flattened out and showed numerous filopodia.

In addition, huge amounts of macrophages at sites of attempted phagocytosis were observed. The conclusion that was drawn is that long, but not short, carbon nanotubes can affect the macrophage function. Being exposed to carbon nanotubes does not only activate their bioreactivity, but also reduces the ability to phagocytose bacteria. This result stands in contrast to observation with short carbon nanotubes.

Hopefully these two examples illustrate how observations performed with a SEM can be beneficial for cell biological investigations.

Speaking of observations through a scanning electron microscope, take a look at our new quiz ‘Guess the size’.

This 5-minute quiz challenges you to test out your sizing skills by letting you guess the sizes of 12 objects magnified by a SEM. Do you think you can get top score and seize giant glory?

Take the quiz


References

[1] Is EM dead? – Knott & Genoud, Journal of Cell Science, 126, 2013.

[2] The Golgi matrix protein giantin is required for normal cilia function in zebrafish – Bergen et al., Biology open, 2017.

[3] Functional consequences for primary human alveolar macrophages following treatment with long, but not short, multiwalled carbon nanotubes – Sweeney et al., International Journal of Nanomedicine, 2015.

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