Super Resolution Imaging
Often in science, to understand more, we need to be able to see smaller and in more detail and the smaller you go the more secrets you can unlock. Microscopes have been available to scientists since the late sixteenth century; however, there have been many advances in this area since the beginning of the twentieth century with the development initially of electron microscopy whilst the end of the century saw the development of fluorescence microscopy.
In biology, being able to see smaller and in more detail will assist with key understanding such as the function and interaction of proteins in a cell. Knowledge of this would help make huge progress in areas such as the development of novel drugs.
Using special biomarkers, current techniques in fluorescence microscopy allow us to light up these proteins and see where there are in the cell; however, the resolution is not sufficient for us to be able to see the individual proteins in action. It’s like looking at the floodlights in a sports stadium, when the lights are on you can see plenty of light, but you can’t see the individual bulbs.
How to overcome this challenge has been a focus of the recent research of Dr Aylin Hanyaloglu. Her key interest has been G protein-coupled receptors (GPCRs). These receptors form more than 3% of the human genome, play an important part in basic functions such as smell, taste and vision and are the target of more than 40% of current prescription drugs. Gonadotrophins are a class of hormones found in all vertebrates and are important in reproduction and pregnancy they also act as a switch for GPCRs. If we were able to see how receptors interacted, this could have huge potential benefits for improving our understanding of the mechanisms in the cell and assist with drug development work.
Current fluorescence microscopy technology allows us to see objects as small as 250nm (80 times smaller than the width of human hair), however, the technology developed by Aylin and her colleagues can reveal detail as small as 8nm, potentially enabling individual interactions between proteins and receptors to be viewed. As in our floodlight example above, it means that the individual light bulbs can now be turned on and off and therefore viewed one by one.
The technology is called PD-PALM (photoactivation localization microscopy with photoactivatable dyes), the technique uses CAGE photoswitchable dyes to enable the fluorescence of single molecules to be switched on and off allowing researchers to potentially view the individual interactions of proteins and receptors in the cell. In Figure 1, (i) a PD-PALM microscopy image of 4 individual receptors labeled at it's 'tip' with dye (yellow and blue dots) and associating as a tetramer. The white scale bar is 50 nm. The entire receptor molecule in this arrangement of dots are 'unveiled' by computer modelling (ii). Images taken from Jonas et al (2015) J Biol Chem.
Aylin’s work has been highly successful so far and attracted much interest, she has organised a Biochemical Society Workshop on the subject which attracted sponsorship from Zeiss and Hamamatsu and the work has also been selected as Paper of the week in the Journal of Biological Chemistry.