The structure of Nijmegen-breakage syndrome protein 1

This project is now closed

Targeting axons to a synaptic layer

Project supervisor: Iris Salecker (Molecular Neurobiology)

Neural circuits in many brain areas of vertebrates and invertebrates share a striking organization into parallel synaptic layers. These are essential units for both development and function, as they bring potential synaptic partners into close vicinity and enable parallel information processing of sensory input. However, despite their significance, our understanding as to how laminated circuits form in the developing brain is still limited.

To gain insights into the underlying molecular mechanisms, we use the visual system of Drosophila as a genetic model. In flies, photoreceptor cells (R-cells, R1-R8) extend axons from the retina into two areas of the optic lobe. R1-R6 axons terminate in the lamina, whereas R8 and R7 axons stop in two of ten neuropil layers in the medulla. These layers are assembled stepwise during metamorphosis following interdependent cell-type specific programs. Axons of the color-sensitive R-cell subtype R8 are initially positioned in a temporary layer at the medulla neuropil border, where they pause for approximately 30 hours, and subsequently are guided to their final layer (Hadjieconomou et al, 2011a).

Extending our earlier studies (Timofeev et al, 2012), this project seeks to identify determinants, which control pausing and timely release of R8 axons from their temporary layer. Using a RNA interference-based screen, we have isolated a set of genes encoding secreted and membrane-bound molecules, whose knock-down causes conspicuous R8 axon targeting defects during early pupal development. The aim of this PhD project will be to investigate the requirement of one such candidate gene in regulating R8 axon targeting steps and specifically explore its potential role in mediating interactions with target neurons or glial cells.

Training will be provided in a range of experimental strategies including advanced genetics such as the Flybow approach (Hadjieconomou et al, 2011b), molecular cloning techniques, transgenesis, and laser confocal imaging of fixed and live samples.

Optic lobes during early development

Optic lobes during early development

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Examples of optic lobes during early pupal development, in which selected molecules have been knocked-down using expression of RNA interference transgenes in R-cells and target neurons. Photoreceptor axons are visualized with mAb24B10 (red), areas of knock-down are labeled with green fluorescent protein (green). (A) R8 and R7 axons correctly pause in their temporary neuropil layers in the medulla, indicating that the knock-down has no effect. (B) R8 axons project incorrectly towards the layer innervated by R7 axons (arrows), implicating the affected determinant in controlling early R8 axon-targeting steps.

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