New method marks receptor proteins in selected cells

Where is a certain receptor protein located in a nerve cell? Without an answer to this question, it is difficult to draw firm conclusions about the function of this protein. Two scientists at the Max Planck Institute for Neurobiology developed a method in the fruit fly that marks receptor proteins in selected cells. In this way, they gained new insights into the neural mechanisms of motion vision. In addition, the research community receives an innovative instrument for labeling proteins of all kinds.

One of the most fundamental questions in neurobiology is how sensory input is processed in the brain’s neural circuits. It is not only important to understand which neurons are connected via synapses, but also how they communicate with one another. Receptors play a crucial role in this.

These special proteins are located in the membrane covering of neurons and especially at synapses, where they receive incoming signals from other cells. Depending on the receptor type and position, they determine how the cells react to incoming information: Are they activated or inhibited and how quickly does this happen? In order to understand a neural network in its entirety, it is therefore important to study receptors and their distribution in neurons. However, this is not an easy task.

Some established methods provide little or no information about the distribution of proteins. Other techniques allow labeling of receptors that are artificially introduced into cells, but not naturally occurring ones. Therefore, PhD students Sandra Fendl and Renee Vieira from the Alexander Borst department used the genetic resources of the Drosophila fruit fly and developed a method for labeling proteins.

With the new technology, endogenous receptors are marked with the green fluorescent protein – and only in selected cells. The latter is essential for the assignment of the marked receptors within the dense neural network to the cells that are of particular interest.

Using this method, the scientists analyzed receptors in neurons that process movements in the fruit fly’s visual system. They found that different receptors are not randomly arranged along neurons. Even within a dendrite, the part of a neuron that receives incoming signals, receptor proteins are distributed in very characteristic ways.

The study shows with an accuracy of a few micrometers which synapse meets which receptor along the dendrite. Now predictions can be made about the properties of individual nerve cell connections. This adds another important piece of the puzzle to a full picture of the neural circuitry in the fruit fly’s visual system.

But that’s not all: the new tool can easily be expanded to include thousands of other proteins. In the future, countless proteins in selected cells can be labeled and examined – and this goes well beyond the specific neurobiological question of fly movement vision.