Stage M2 : "Identification and characterization of a wild-derived mutation affecting photoreceptor neuron identities in the adult Drosophila retina."
5 Mots clés :
Drosophile, Variabilité génétique, Retine, Neurone photoreceptor, Rhodopsin
Responsable de l'équipe d'appui/Maître de stage : Vasiliauskas, Daniel
Intitulé et adresse du laboratoire :
Neurogénétique chez la Drosophile
Institut des Neurosciences Paris-Saclay - UMR 9197 / CNRS
CNRS - Délégation Ile-de-France Sud (DR04)
1, Avenue de la Terrasse
Description du stage :
Colour photoreceptor neurons of the fly retina has proven to be an excellent system for studying mechanisms which establish and maintain distinct functional identities of closely related neuronal types. Our lab focused on the R8 photoreceptor type, with its two subtypes p and y. The cells of the two subtypes express distinct Rhodopsins (Rh, a G-protein coupled receptor that acts as a photon receptor) which define their spectral sensitivities: pR8 cells express the "blue-sensitive" Rh5, while yR8 express the "green-sensitive" Rh6. (See reference 1 for images of what this looks like in the eye and for more details about the system.) The developmental program that leads to this mutually exclusive expression pattern has been relatively well understood (1) although a number of interesting unresolved questions remain. For example: The mutually exclusive Rh5/Rh6 expression is established through a bistable positive feedback-driven genetic switch which turns ON (for Rh6) or OFF (for Rh5) the Hippo tumor supressor pathway activity. The involvement of this pathway is curious, because in most other systems, it regulates growth and cell prolifferation through negative feedbacks that drive the pathway towards equilibrium (like a thermostat, i.e. in sharp contrast to the bistability observed in the photoreceptors).
To identify new genes involved in establishment and maintenance of Rh5/Rh6 expression pattern we took an unusual approach: we examined ~200 fly lines recently derived from wild-caught flies. We identified a number of interesting phenotypes that affect differentiation, maintenance and function of the R8 photoreceptor neurons. One line in particular, has a reversed p:y cell ratio (see figure) and is similar to the loss of the Hippo pathway phenotypes (which are normally lethal). Identification of the sequence change resulting in this phenotype will provide an interesting example of what type of natural genetic variation can affect a single function of this essential pathway without affecting its other roles. This is fundamental to understanding how pathways can independently evolve multiple functions.
The M2 student will use powerful Drosophila genetics to identify the gene affected by the mutation and then will identify the mutation itself. In parallel, he or she will characterize the phenotype in order to understand the mechanisms underlying it. The experiments will involve genetics, immunohistochemistry (antibody stains) of whole fly retinas and confocal microscopy.
1. Rister, J., Desplan, C., and Vasiliauskas, D. (2013) Establishing and maintaining gene expression patterns: insights from sensory receptor patterning. Development 140, 493-503.
2. Vasiliauskas, D., Mazzoni, E.O., Sprecher, S.G., Brodetskiy, K., Johnston, R.J.Jr., Lidder, P., Vogt, N., Celik, A., and Desplan, C. (2011) Feedback from Rhodopsin controls rhodopsin exclusion in Drosophila photoreceptors. Nature, 479, 108-12.
Candidature à :
sous la référence "www.123bio.eu/stage_M2"