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In order to understand us as humans, and how the world around us functions, scientists want to investigate the inner workings of a cell. While what occurs in these tiny entities is miraculous, visualizing these processes in real-time is no easy feat; a relatively new imaging platform called lattice light sheet microscopy is making the task a little easier.
Developed by Eric Betzig – noted for his Nobel Prize in Chemistry in 2014 for the development of super-resolved fluorescence microscopy – lattice light sheet microscopy (LLSM) makes use of a lattice pattern of thin light beams. It uses a structured light sheet to excite fluorescence in successive planes of a specimen, enabling the capture of a time series of three-dimensional images offering information on dynamic biological processes.
LLSM is a novel combination of techniques and evolved from Betzig’s Bessel beam plane illumination microscope, which illuminates samples with a virtual sheet of light, created when a beam of non-diffracting light – a so-called Bessel beam - sweeps across the imaging field to produce high-resolution images.
The use of a lattice network of thin light beams reduces the total amount of light delivered to a sample and thus minimises phototoxicity. One of the chief challenges encountered by scientists when studying live cells is being able to perceive them without upsetting their behaviour. LLSM overcomes this by reducing a cell’s exposure to light using a plane of illumination rather than a point of light.
LLSM couples a separate excitation lens in a perpendicular axis to the detection lens, meaning it is possible to confine the excitation of the specimen being observed therefore reducing the phototoxicity and increasing the speed of image acquisition.
This decrease in phototoxicity allows scientists to investigate subcellular processes and permits the three-dimensional imaging of molecules, cells and even embryos in incredibly fine detail for longer periods of time than was previously possible – all without damaging the living tissues. Not only does LLSM allow for the imaging of three-dimensional dynamic processes in vivo, it also offers advantages in speed and sensitivity compared to other microscopy methods and allows temperature, carbon dioxide and humidity levels to be maintained.
LLSM is used for observing a number of dynamic cellular interactions and allows for more precise, detailed study of cells and the creation of continuous fluorescence movies of developing organisms, thus enabling scientists to track the movements of individual proteins in 3D, the growth and division of cells and the molecular dynamics of developmental processes.
The technique has been used to visualise membrane nanotubes, which provide a means of communication between cells utilising soluble messengers such as endocrine signalling. Their role in cancer progression, specifically breast cancer, and resistance to therapies has been investigated by researchers from the University of California, Irvine, who used LLSM to show that cultured cells form multiple nanotubes that mediate intercellular communication of Ca2+signals between cells and traffic GFP tagged membrane aggregates.
It has also been used to image membrane dynamics i.e. the splitting of cells into compartments, and then later two cells, during mitosis. Scientists from Harvard Medical School employed LLSM to study the dynamics of clathrin pit formation in the plasma membrane on the cell surface, finding that such pits form at a lower rate during late mitosis.
The potential applications of LLMS are potentially limitless: however, to ensure good image quality is achieved, LLSM is currently limited to transparent and thin samples. Quality degrades the deeper within a sample the images are taken due to sample induced aberrations and defects. The technique is being actively developed, and combined with other to techniques to allow penetration deeper in to materials.
References and further reading
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