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Dendritic targeting in the leg neuropil of Drosophila: the role of midline signalling molecules in generating a myotopic map.

Brierley DJ, Blanc E, Reddy OV, Vijayraghavan K, Williams DW - PLoS Biol. (2009)

Bottom Line: Thus the cellular distinctions in peripheral targets and central dendritic domains, which make up the myotopic map, are linked to the birth-order of these motoneurons.Our developmental analysis of dendrite growth reveals that this myotopic map is generated by targeting.We demonstrate that the medio-lateral positioning of motoneuron dendrites in the leg neuropil is controlled by the midline signalling systems Slit-Robo and Netrin-Fra.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council (MRC) Centre for Developmental Neurobiology, King's College London, London, United Kingdom.

ABSTRACT
Neural maps are emergent, highly ordered structures that are essential for organizing and presenting synaptic information. Within the embryonic nervous system of Drosophila motoneuron dendrites are organized topographically as a myotopic map that reflects their pattern of innervation in the muscle field. Here we reveal that this fundamental organizational principle exists in adult Drosophila, where the dendrites of leg motoneurons also generate a myotopic map. A single postembryonic neuroblast sequentially generates different leg motoneuron subtypes, starting with those innervating proximal targets and medial neuropil regions and producing progeny that innervate distal muscle targets and lateral neuropil later in the lineage. Thus the cellular distinctions in peripheral targets and central dendritic domains, which make up the myotopic map, are linked to the birth-order of these motoneurons. Our developmental analysis of dendrite growth reveals that this myotopic map is generated by targeting. We demonstrate that the medio-lateral positioning of motoneuron dendrites in the leg neuropil is controlled by the midline signalling systems Slit-Robo and Netrin-Fra. These results reveal that dendritic targeting plays a major role in the formation of myotopic maps and suggests that the coordinate spatial control of both pre- and postsynaptic elements by global neuropilar signals may be an important mechanism for establishing the specificity of synaptic connections.

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Slit and Netrin are required for motoneuron dendritic targeting.(A) VGN9281-GAL4 expressing CD8::GFP. The motoneuron labelled by VGN9281-GAL4 targets dendrites to lateral territories of the leg neuropil. (B) VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Expressing Slit-RNAi in the motoneuron has no effect on medio-lateral distribution of its dendrites. (C) Slit-GAL4 and VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Reducing Slit protein in the midline cells results in dendrites of the VGN9281-GAL4 motoneuron being shifted into intermediate and medial territories. (D) Expressing CD8::GFP and NetrinB under the control of Slit-GAL4 and VGN9281-GAL4 does not change the medio-lateral position of the dendrites of the motoneuron. (E) VGN9281-GAL4 expressing CD8::GFP in NetABΔ background. The dendrites of the VGN9281-GAL4 motoneuron do not change position in a NetABΔ background. (F) E49-GAL4 expressing CD8::GFP reveals the bulk of the motoneurons of the prothoracic neuromere. The dendrites of the motoneurons that innervate the pretarsal flexor muscles approach and cross the midline. Boxed area detail shown in F'. (G) E49-GAL4 expressing CD8::GFP in a NetABΔ background reveals the dendrites of the pretarsal flexor muscle motoneurons fail to approach and cross the midline. Asterisk denotes anterior part of neuropil where dendrites fail to approach the midline. Boxed area detail shown in G'. (F') Detail from F. (G') Detail from G. Scale bars = 20 µm. Scale bar in E applies for A–E. Scale bar in G applies to F. Scale bar in G' applies to F'.
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pbio-1000199-g006: Slit and Netrin are required for motoneuron dendritic targeting.(A) VGN9281-GAL4 expressing CD8::GFP. The motoneuron labelled by VGN9281-GAL4 targets dendrites to lateral territories of the leg neuropil. (B) VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Expressing Slit-RNAi in the motoneuron has no effect on medio-lateral distribution of its dendrites. (C) Slit-GAL4 and VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Reducing Slit protein in the midline cells results in dendrites of the VGN9281-GAL4 motoneuron being shifted into intermediate and medial territories. (D) Expressing CD8::GFP and NetrinB under the control of Slit-GAL4 and VGN9281-GAL4 does not change the medio-lateral position of the dendrites of the motoneuron. (E) VGN9281-GAL4 expressing CD8::GFP in NetABΔ background. The dendrites of the VGN9281-GAL4 motoneuron do not change position in a NetABΔ background. (F) E49-GAL4 expressing CD8::GFP reveals the bulk of the motoneurons of the prothoracic neuromere. The dendrites of the motoneurons that innervate the pretarsal flexor muscles approach and cross the midline. Boxed area detail shown in F'. (G) E49-GAL4 expressing CD8::GFP in a NetABΔ background reveals the dendrites of the pretarsal flexor muscle motoneurons fail to approach and cross the midline. Asterisk denotes anterior part of neuropil where dendrites fail to approach the midline. Boxed area detail shown in G'. (F') Detail from F. (G') Detail from G. Scale bars = 20 µm. Scale bar in E applies for A–E. Scale bar in G applies to F. Scale bar in G' applies to F'.

Mentions: Slit s are homozygous lethal and this prevented us from performing analysis on adult motoneuron dendrites. To overcome this we have established a method to conditionally knock down Slit using RNAi during adult development. To do this we expressed Slit RNAi in the midline cells under the control of the Slit-GAL4 driver. As described above our antibody staining revealed that Slit is not detectable by 48 h APF in such animals (Figure 3C). To visualize a late-born neuron we used VGN9281-GAL4, which contains a fragment of the Drosophila VGlut cis-regulatory region. As well as labelling a late-born cell of the 96 h AH subtype (Figure 6A), it also expresses GAL4 in a small number of interneurons. Using this tool we were able to knock down Slit protein (Slit-GAL4>UAS Slit RNAi) and simultaneously visualize the dendrites of the motoneuron labelled by VGN9281-GAL4. We found that when we removed Slit, the dendrites of the motoneuron shifted into intermediate and medial neuropil territories with several branches projecting to and terminating at the midline (Figure 6C). As a control we expressed UAS-Slit RNAi in VGN9281-GAL4 alone and found the distribution of the dendrites the same as wild-type (Figure 6B).


Dendritic targeting in the leg neuropil of Drosophila: the role of midline signalling molecules in generating a myotopic map.

Brierley DJ, Blanc E, Reddy OV, Vijayraghavan K, Williams DW - PLoS Biol. (2009)

Slit and Netrin are required for motoneuron dendritic targeting.(A) VGN9281-GAL4 expressing CD8::GFP. The motoneuron labelled by VGN9281-GAL4 targets dendrites to lateral territories of the leg neuropil. (B) VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Expressing Slit-RNAi in the motoneuron has no effect on medio-lateral distribution of its dendrites. (C) Slit-GAL4 and VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Reducing Slit protein in the midline cells results in dendrites of the VGN9281-GAL4 motoneuron being shifted into intermediate and medial territories. (D) Expressing CD8::GFP and NetrinB under the control of Slit-GAL4 and VGN9281-GAL4 does not change the medio-lateral position of the dendrites of the motoneuron. (E) VGN9281-GAL4 expressing CD8::GFP in NetABΔ background. The dendrites of the VGN9281-GAL4 motoneuron do not change position in a NetABΔ background. (F) E49-GAL4 expressing CD8::GFP reveals the bulk of the motoneurons of the prothoracic neuromere. The dendrites of the motoneurons that innervate the pretarsal flexor muscles approach and cross the midline. Boxed area detail shown in F'. (G) E49-GAL4 expressing CD8::GFP in a NetABΔ background reveals the dendrites of the pretarsal flexor muscle motoneurons fail to approach and cross the midline. Asterisk denotes anterior part of neuropil where dendrites fail to approach the midline. Boxed area detail shown in G'. (F') Detail from F. (G') Detail from G. Scale bars = 20 µm. Scale bar in E applies for A–E. Scale bar in G applies to F. Scale bar in G' applies to F'.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2737123&req=5

pbio-1000199-g006: Slit and Netrin are required for motoneuron dendritic targeting.(A) VGN9281-GAL4 expressing CD8::GFP. The motoneuron labelled by VGN9281-GAL4 targets dendrites to lateral territories of the leg neuropil. (B) VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Expressing Slit-RNAi in the motoneuron has no effect on medio-lateral distribution of its dendrites. (C) Slit-GAL4 and VGN9281-GAL4 expressing CD8::GFP and Slit-RNAi. Reducing Slit protein in the midline cells results in dendrites of the VGN9281-GAL4 motoneuron being shifted into intermediate and medial territories. (D) Expressing CD8::GFP and NetrinB under the control of Slit-GAL4 and VGN9281-GAL4 does not change the medio-lateral position of the dendrites of the motoneuron. (E) VGN9281-GAL4 expressing CD8::GFP in NetABΔ background. The dendrites of the VGN9281-GAL4 motoneuron do not change position in a NetABΔ background. (F) E49-GAL4 expressing CD8::GFP reveals the bulk of the motoneurons of the prothoracic neuromere. The dendrites of the motoneurons that innervate the pretarsal flexor muscles approach and cross the midline. Boxed area detail shown in F'. (G) E49-GAL4 expressing CD8::GFP in a NetABΔ background reveals the dendrites of the pretarsal flexor muscle motoneurons fail to approach and cross the midline. Asterisk denotes anterior part of neuropil where dendrites fail to approach the midline. Boxed area detail shown in G'. (F') Detail from F. (G') Detail from G. Scale bars = 20 µm. Scale bar in E applies for A–E. Scale bar in G applies to F. Scale bar in G' applies to F'.
Mentions: Slit s are homozygous lethal and this prevented us from performing analysis on adult motoneuron dendrites. To overcome this we have established a method to conditionally knock down Slit using RNAi during adult development. To do this we expressed Slit RNAi in the midline cells under the control of the Slit-GAL4 driver. As described above our antibody staining revealed that Slit is not detectable by 48 h APF in such animals (Figure 3C). To visualize a late-born neuron we used VGN9281-GAL4, which contains a fragment of the Drosophila VGlut cis-regulatory region. As well as labelling a late-born cell of the 96 h AH subtype (Figure 6A), it also expresses GAL4 in a small number of interneurons. Using this tool we were able to knock down Slit protein (Slit-GAL4>UAS Slit RNAi) and simultaneously visualize the dendrites of the motoneuron labelled by VGN9281-GAL4. We found that when we removed Slit, the dendrites of the motoneuron shifted into intermediate and medial neuropil territories with several branches projecting to and terminating at the midline (Figure 6C). As a control we expressed UAS-Slit RNAi in VGN9281-GAL4 alone and found the distribution of the dendrites the same as wild-type (Figure 6B).

Bottom Line: Thus the cellular distinctions in peripheral targets and central dendritic domains, which make up the myotopic map, are linked to the birth-order of these motoneurons.Our developmental analysis of dendrite growth reveals that this myotopic map is generated by targeting.We demonstrate that the medio-lateral positioning of motoneuron dendrites in the leg neuropil is controlled by the midline signalling systems Slit-Robo and Netrin-Fra.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council (MRC) Centre for Developmental Neurobiology, King's College London, London, United Kingdom.

ABSTRACT
Neural maps are emergent, highly ordered structures that are essential for organizing and presenting synaptic information. Within the embryonic nervous system of Drosophila motoneuron dendrites are organized topographically as a myotopic map that reflects their pattern of innervation in the muscle field. Here we reveal that this fundamental organizational principle exists in adult Drosophila, where the dendrites of leg motoneurons also generate a myotopic map. A single postembryonic neuroblast sequentially generates different leg motoneuron subtypes, starting with those innervating proximal targets and medial neuropil regions and producing progeny that innervate distal muscle targets and lateral neuropil later in the lineage. Thus the cellular distinctions in peripheral targets and central dendritic domains, which make up the myotopic map, are linked to the birth-order of these motoneurons. Our developmental analysis of dendrite growth reveals that this myotopic map is generated by targeting. We demonstrate that the medio-lateral positioning of motoneuron dendrites in the leg neuropil is controlled by the midline signalling systems Slit-Robo and Netrin-Fra. These results reveal that dendritic targeting plays a major role in the formation of myotopic maps and suggests that the coordinate spatial control of both pre- and postsynaptic elements by global neuropilar signals may be an important mechanism for establishing the specificity of synaptic connections.

Show MeSH