First published online for Germany’s Year of Light 2015, here is what I do these days.
Did you know that humans are genetically similar worms? Some worm genes make proteins that are similar to proteins in humans. Scientists at Max Planck Institute of Molecular Cell Biology and Genetics are using the worm, C. elegans, to study these proteins in hopes of gaining a better understanding of how the proteins function in humans.
C. elegans is a nematode worm. It can be found in nutrient rich soil often feeding on bacteria that thrive on decaying organic matter. Although lacking a circulatory and respiratory system, the worm has a mouth, pharynx, intestines and a nervous system. As an adult worm, it only grows to about 1mm in length. This tiny worm can generate over 20,000 proteins throughout its life. If we can understand how these proteins function in C. elegans we may be able to draw the same conclusions about their functions in human.
Above: C. elegans worms with a GFP tagged protein, syp-1. The green is the protein and the blue is the DNA inside the worm. Syp-1 plays a role in pairing chromosomes during meiosis. Top Left: egg, Top Right: Three worms at larvae stage 1, Bottom Left: Midsection of larvae stage 4, Bottom Right: Tail of adult. Taken by Me, while in the Transgeneomics Facility/Sarov Lab – MPI-CBG.
Imaging this creature’s proteins is a fairly simplified task as the worm is transparent, making it perfect for microscopy work. But how do we distinguish between different proteins in the worm? And how do we get the best image possible? We use light.
Imagine if we could light up one specific protein in the entire worm, essentially creating a glowing worm that we could use to study one protein at a time under a microscope. Well that is what the scientists at MPI have done. Using molecular biology techniques, they have attached a green fluorescent tag (or green fluorescent protein – GFP) to a worm protein that exists also in humans. And they have done this for many different proteins. The GFP tag makes the protein glow green under fluorescent light and allows the scientists to track the protein inside the worm.
The particular microscopy method employed to study these fluorescent worm proteins is known as SPIM. SPIM stands for Selective Plane Illumination Microscopy and uses sheets of light perpendicular to the detection lens to bring a specimen in to focus. This is different from other microscopes in many ways. It allows the scientist to avoid a lot of photo bleaching – a phenomenon where light fades the fluorescence in a sample, rendering it unusable. The light sheet SPIM also allows for quick 360o imaging and 3D reconstruction of specimens.
The scientists at MPI used SPIM to take pictures of many different GFP tagged proteins in C. elegans. A thin sheet of fluorescent light illuminates a tiny section along the worm body. Every other part of the worm is in the dark. If a fluorescent protein is present in this tiny lit up section, it will become visible. The light is repositioned on a different tiny section along the worm body and pictures are taken in this fashion along the entire length of the worm, from head to tail. The worm is also rotated a full 360o while pictures are being acquired via the light sheet illumination. After all of the 2D pictures are taken, a computer program uses the fluorescent light data in each image to construct the pictures into a final 3D image.
One goal of these images is to complete an interactive Pictionary of worm proteins, providing a visual tool to track where specific proteins are located during the different stages of the worm life cycle. Viewing the 3D image on a computer, one can rotate the worm in the x, y and z-axis allowing the visualization of one specific protein throughout the entire worm. This provides a multitude of answers to questions about worm proteins. How much of Protein A is present in the head of the worm as opposed to the body or the tail? Is Protein B always in the head of the worm or does its position change throughout the worm’s life cycle? Is it possible that Protein A and Protein B interact with each other?
If we can make conclusions about these human-like worm proteins, we will gain an understanding of how these proteins function in humans. This alone could lead to medical advancements in treating human diseases such as Alzheimer’s disease, spinal muscular atrophy, Parkinson’s disease and cancer.