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Fig. 5 | Neural Development

Fig. 5

From: Strategies for assembling columns and layers in the Drosophila visual system

Fig. 5

Outer layers develop in a stepwise manner from broad domains. h APF = hours after puparium formation (a) A representation of the adult morphologies of lamina neuron axons L1-L5. The arborizations of lamina neuron axons help define specific outer medulla layers. (b) A drawing of lamina neuron growth cones L1-L5 in early pupal development. Prior to arborizing in discrete layers lamina growth cones terminate in distal or proximal domains within the outer medulla. (c) An illustration of M2 development. A CadN-dependent interaction between the axons of lamina neurons L2 and L5 mediates the branching of L5 axons into the M2 layer. (d) A diagram of M3 development. The M3 layer develops in part through the sequential innervation of L3 and R8 axons. DFezf cell autonomously promotes the targeting of L3 growth cones to the proximal domain of the outer medulla. L3 growth cones then segregate into the developing M3 layer in part through repulsion from medulla tangential fibers (MeT). DFezf activates the expression of Netrin which is secreted from L3 growth cones, and serves as an M3-specific cue for R8 growth cones. (Arrows in the second panel from the left indicate the retraction of the leading edge of an L3 growth cone, and extension of filopodia laterally across the column within the developing M3 layer. The arrow in the third and fourth panels from the left show the secretion of Netrin from L3 growth cones, which becomes concentrated within the developing M3 layer)

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