An electroretinogram (ERG) records the change in electrical activity of a photoreceptor in response to light exposure. Whereas human photoreceptors are light-detecting cells in the retina that connect to a neuron, Drosophila photoreceptors themselves are the neurons. Therefore, ERGs are easily accessible in Drosophila. ERGs are used in mutant Drosophila to identify genes involved in phototransduction and neurodegeneration.

Electroretinogram (ERG)

As NMJ electrophysiology is performed in third instar larvae, the method is not easily applied to longitudinal studies. The giant fiber system (GFS) in adult flies, however, is amenable to in vivo electrophysiology. Electrodes are applied to the eye, stimulating the giant fiber neurons in the brain. The GFS then activates the fly’s “flight” muscles in response to change in light exposure. GFS recordings have been used to study epilepsy and seizures.

Giant-fiber-system Recordings

Neuromuscular junction (NMJ) electrophysiology is performed on Drosophila third instar larvae to study human diseases characterized by abnormal electrophysiology, such as epilepsy and ALS. The larva is fileted down the length of its body to expose the ventral nerve cord and body wall muscles. Electrodes are then inserted into a motor neuron and a corresponding body wall muscle. This method of studying the NMJ is accurate, but difficult and labor-intensive, so electrophysiology is combined with genetic screens to fully characterize NMJ mutations.

Neuromuscular Junction Electrophysiology

The Drosophila wing injury assay is used to study axonal de-/regeneration in vivo. Cutting the wing severs the axon, causing axonal degeneration. However, after approximately a week, the injured axons regenerate by extending new sprouts toward the site of injury. Forward genetic screens can be combined with wing injury assays to identify genes responsible for axonal development.

Wing Injury Assay

- Electroretinogram (ERG)
- Neuromuscular junction electrophysiology
- Giant-fiber-system recordings
- Wing injury assay


Pomona College

 Drosophila melanogaster (fruit flies) are valuable model organisms for studying mechanisms underlying development and human disease. Like C. elegans, Drosophila are favored models due to their short generation time, high rate of reproduction, and convenient maintenance within the laboratory. Around 65% of genes that cause disease in humans have functional homologs in flies, and 38 of 59 human neurological genes have orthologs in flies. Additionally, the Drosophila genome has been fully sequenced, allowing for more precision when manipulating genes.

Drosophila melanogaster (fruit fly)

Ugur, B., Chen, K., & Bellen, H. J. (2016). Drosophila tools and assays for the study of human diseases. Disease Models & Mechanisms, 9(3), 235–244. https://doi.org/10.1242/dmm.023762

Drosophila tools and assays for the study of human diseases (2016)

- Reverse genetics
- Forward genetics
- Diagnostic strategy

Genetic tools for Drosophila

 The chemotaxis assay is used to study C. elegans olfactory behavior. The odorant or chemical of study is applied to one side of the agar plate, with a control chemical applied to the opposite side. Sodium azide is added to both sides to immobilize the worms upon reaching their chosen odorant. Worms are placed equidistant from either chemical and allowed to chemotax, or roam freely, for a set period of time (roughly an hour to ensure the sodium azide immobilizes all worms). A chemotaxis index is calculated by subtracting the number of worms on the control zone from the number of worms on the odorant zone, divided by the total number of worms. Therefore, a chemotaxis close to 1 indicates a strong preference for the odorant, while a value close to -1 indicates either a strong repulsion to the odorant, or a lack of preference in general. This assay is also applicable to Drosophila larvae, and can be adapted to study more complex behaviors such as associative learning.

Learn Before

Related

Learn After