Looking at mRNA in fruit flies

mRNA particles in a Drosophila neuron. The outline of the nerve cell is tinted green. The large pink dot in the middle is the cell's nucleus, and the individual pink dots outside the nucleus are mRNA particles (arrows).
© Rode/Rumpf

Project title: Novel tools for mRNA labeling in Drosophila
Principal investigators: Sebastian Rumpf, Andrea Rentmeister
Project time: 07/2016 - 10/2018
Project code: FF-2016-13

Biologists and chemists work closely together in this project. Their aim is to visualize a biomolecule which is found in cells and which plays a decisive role for all functions in the cell: the messenger RNA or, for short, mRNA.

Dr. Sebastian Rumpf, a biologist, is investigating the degradation of neuronal processes, the axons and dendrites, which enable nerve cells to connect with each other and to pass on signals. This process of breaking down non-specific neuronal processes is called “pruning” and is important for the development of the nervous system. Sebastian Rumpf and his colleagues are examining the pruning process in larvae of the fruit fly Drosophila melanogaster. In their project they are focusing on a certain gene which plays a role in the breakdown of dendrites: mical. The genetic information is stored on a section of the DNA and – in a so-called transcription process – transcribed into the mRNA, which further transports the genetic information within the cell so that proteins can be made from it. The researchers have discovered that regulating mRNA plays a major part in the expression of mical – and thus in the pruning process. The messenger RNA is often transported to the location within the cell where the encoded protein acts. This is why the researchers want to know where the mical mRNA is localized within nerve cells.

This is where Prof. Andrea Rentmeister, a chemist, comes in. Rentmeister, a CiM professor, develops novel techniques to visualize mRNA. She gave Sebastian Rumpf decisive suggestions which made it possible, for the first time, to see and analyse in vivo the mical mRNA in the nerve cells of the flies. For this purpose, the researchers combined two well-known techniques: using the CRISPR method, which makes it possible to change DNA sequences, they inserted into the mical gene short target sequences. Once transcribed into mRNA, these sequences can be bound by specific marker proteins, thus enabling the researchers to label the mical mRNA with fluorescent proteins. This process is called the MS2 method. Observing the mRNA is designed to help the Sebastian Rumpf’s team of biologists to gain a better understanding of the mechanisms which are responsible for regulating the mical gene and thus for the breakdown of the nerve cell processes.

Moreover, the team of biochemists headed by Andrea Rentmeister is developing a new kind of method to visualize mRNA: chemical mRNA cap-labeling. The process is based on the concept of click chemistry. This enables installation of molecular labels in biomolecules, based on selected chemical reactions that do not disrupt the biological processes in the cell or produce unwanted by-products. The researchers are attempting in their project to transfer the experiments from the test-tube to the fruit fly as an animal model. The biologists are now, on the one hand, developing fly-lines with specific enzymes which label and change the so-called cap structure of the mRNA. The mRNA cap plays an important part for their function. And, on the other hand, the researchers are testing how the chemicals for the labelling in the flies behave, and, as a result, how individual mRNAs can be labelled and visualized.