Competition and position-dependent targeting in the development of the Drosophila R7 visual projections

Area of Science:

• Neuroscience
• Developmental Biology
• Genetics

Background:

• The R7 photoreceptor neuron projections in Drosophila form a retinotopic map in the medulla.
• The "more inner photoreceptors" mutation causes excess R7 photoreceptor differentiation.

Purpose of the Study:

• Explore roles of photoreceptor-target regulation, competitive interactions, and chemoaffinity in retinotopic map formation.
• Utilize a Drosophila R7 hyperinnervation model to investigate neural map development.

Main Methods:

• Analysis of the "more inner photoreceptors" mutation in Drosophila.
• Examination of R7 photoreceptor axon targeting in wild-type and mosaic eyes.
• Observation of R7/R8 axon filopodia and targeting in sine oculis mutant larvae.

Main Results:

• Target regulation of presynaptic population size was not observed.
• R7 axons target appropriate locations even in largely empty fields, suggesting chemoaffinity.
• Competitive interactions appear to restrain axons to single termination sites.
• Eye position influences connectivity, independent of neighboring R7/R8 axons.

Conclusions:

• Drosophila retinotopic map development shares mechanisms with vertebrates.
• Competitive interactions and positional information are crucial for precise neural map formation.
• This genetic model facilitates understanding molecular mechanisms of retinotopic map development.