@article {65032,
	title = {Robo-3--mediated repulsive interactions guide R8 axons during Drosophila visual system development.},
	journal = {Proc Natl Acad Sci U S A},
	volume = {108},
	year = {2011},
	month = {2011 May 03},
	pages = {7571-6},
	abstract = {<p>The formation of neuronal connections requires the precise guidance of developing axons toward their targets. In the Drosophila visual system, photoreceptor neurons (R cells) project from the eye into the brain. These cells are grouped into some 750 clusters comprised of eight photoreceptors or R cells each. R cells fall into three classes: R1 to R6, R7, and R8. Posterior R8 cells are the first to project axons into the brain. How these axons select a specific pathway is not known. Here, we used a microarray-based approach to identify genes expressed in R8 neurons as they extend into the brain. We found that Roundabout-3 (Robo3), an axon-guidance receptor, is expressed specifically and transiently in R8 growth cones. In wild-type animals, posterior-most R8 axons extend along a border of glial cells demarcated by the expression of Slit, the secreted ligand of Robo3. In contrast, robo3 mutant R8 axons extend across this border and fasciculate inappropriately with other axon tracts. We demonstrate that either Robo1 or Robo2 rescues the robo3 mutant phenotype when each is knocked into the endogenous robo3 locus separately, indicating that R8 does not require a function unique to the Robo3 paralog. However, persistent expression of Robo3 in R8 disrupts the layer-specific targeting of R8 growth cones. Thus, the transient cell-specific expression of Robo3 plays a crucial role in establishing neural circuits in the Drosophila visual system by selectively regulating pathway choice for posterior-most R8 growth cones.</p>
},
	keywords = {Animals, Axons, Drosophila, Drosophila Proteins, Growth Cones, Image Processing, Computer-Assisted, Immunohistochemistry, Microarray Analysis, Nerve Tissue Proteins, Photoreceptor Cells, Invertebrate, Receptors, Immunologic, Visual Pathways},
	issn = {1091-6490},
	doi = {10.1073/pnas.1103419108},
	author = {Pappu, Kartik S and Morey, Marta and Nern, Aljoscha and Spitzweck, Bettina and Dickson, Barry J and Zipursky, S L}
}
@article {6861,
	title = {Distinct protein domains and expression patterns confer divergent axon guidance functions for Drosophila Robo receptors.},
	journal = {Cell},
	volume = {140},
	year = {2010},
	month = {2010 Feb 5},
	pages = {409-20},
	abstract = {<p>The orthogonal array of axon pathways in the Drosophila CNS is constructed in part under the control of three Robo family axon guidance receptors: Robo1, Robo2 and Robo3. Each of these receptors is responsible for a distinct set of guidance decisions. To determine the molecular basis for these functional specializations, we used homologous recombination to create a series of 9 "robo swap" alleles: expressing each of the three Robo receptors from each of the three robo loci. We demonstrate that the lateral positioning of longitudinal axon pathways relies primarily on differences in gene regulation, not distinct combinations of Robo proteins as previously thought. In contrast, specific features of the Robo1 and Robo2 proteins contribute to their distinct functions in commissure formation. These specializations allow Robo1 to prevent crossing and Robo2 to promote crossing. These data demonstrate how diversification of expression and structure within a single family of guidance receptors can shape complex patterns of neuronal wiring.</p>
},
	keywords = {Animals, Axons, Central Nervous System, Developmental, Drosophila melanogaster, Drosophila Proteins, Embryo, Gene Expression Regulation, Immunologic, Nerve Tissue Proteins, Nonmammalian, Receptors},
	issn = {1097-4172},
	doi = {10.1016/j.cell.2010.01.002},
	author = {Spitzweck, Bettina and Brankatschk, Marko and Dickson, Barry J}
}
