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Orthodenticle Is Required for the Expression of Principal Recognition Molecules That Control Axon Targeting in the Drosophila Retina.

Mencarelli C, Pichaud F - PLoS Genet. (2015)

Bottom Line: Our data indicate that otd function in these photoreceptors is largely mediated by the recognition molecules flamingo (fmi) and golden goal (gogo).In addition, we find that otd regulates synaptic-layer targeting of R8.Our work therefore demonstrates that otd is a main component of the gene regulatory network that regulates synaptic-column and layer targeting in the fly visual system.

View Article: PubMed Central - PubMed

Affiliation: MRC Laboratory for Molecular Cell Biology, University College London, London, United Kingdom.

ABSTRACT
Parallel processing of neuronal inputs relies on assembling neural circuits into distinct synaptic-columns and layers. This is orchestrated by matching recognition molecules between afferent growth cones and target areas. Controlling the expression of these molecules during development is crucial but not well understood. The developing Drosophila visual system is a powerful genetic model for addressing this question. In this model system, the achromatic R1-6 photoreceptors project their axons in the lamina while the R7 and R8 photoreceptors, which are involved in colour detection, project their axons to two distinct synaptic-layers in the medulla. Here we show that the conserved homeodomain transcription factor Orthodenticle (Otd), which in the eye is a main regulator of rhodopsin expression, is also required for R1-6 photoreceptor synaptic-column specific innervation of the lamina. Our data indicate that otd function in these photoreceptors is largely mediated by the recognition molecules flamingo (fmi) and golden goal (gogo). In addition, we find that otd regulates synaptic-layer targeting of R8. We demonstrate that during this process, otd and the R8-specific transcription factor senseless/Gfi1 (sens) function as independent transcriptional inputs that are required for the expression of fmi, gogo and the adhesion molecule capricious (caps), which govern R8 synaptic-layer targeting. Our work therefore demonstrates that otd is a main component of the gene regulatory network that regulates synaptic-column and layer targeting in the fly visual system.

No MeSH data available.


Related in: MedlinePlus

otd is required for R8 synaptic-layer targeting.Wild-type (A,A’) and otduvi mutant (B,B’) adult optic lobes expressing the R8 specific marker Rh6-lacZ stained with anti-β-galactosidase (green). In wild-type (A,A’) Rh6-lacZ-positive R8 axons terminate in the M3 layer. otduvi mutants (B-B”) display a strong R8 axon misprojection phenotype. R8 axons specifically overshoot to the M6 layer (boxed in B’ and quantified in Fig 5H) while some R8 axons invade neighbouring columns cross-laterally and terminate in abnormal positions (boxed in B”). Several R8 axons terminals can also be seen to stall at more superficial layers and fail to innervate the medulla (double arrows in b”‘). All panels (C-F) show photoreceptor axon projections stained with the 24B10 antibody (red). R8 axons in wild-type (c,c’) and otduvi mutant (D,D’) optic lobes (40% after puparium formation) are visualized using the ato-τ-myc transgene stained with anti-Myc antibody (green). At this early stage of development, in otduvi mutant retina, R8 growth cones fail to stop in the M1 layer and extend specifically to the R7 temporary layer (n = 438 misprojecting axons of 798 R8 axons quantified in the two temporary layers). The staining for ato-τ-Myc is magnified in (C’,D’) and arrows in (D’) indicate misprojecting R8 axons. boss1 mutant (E) and otduvi/boss1 double-mutant (F) retina. Adult optic lobes stained with 24B10 antibody. In (E), residual 24B10 staining in the R7 M6 layer is derived from medulla neurons [44]. (E) boss1 mutant R8 terminate in the R8 recipient layer M3, with only a few R8 targeting to the M6 layer. (F) Most of the otduvi/boss1 double-mutants display a strong R8 mis-projection phenotype in the R7 layer, M6. (G) otduvi mutant flies where Otd expression has been restored specifically in the photoreceptors using the GMRGal4 driver. In this context, staining of the R8 specific marker Rh6-lacZ (green) demonstrates that normal R8 photoreceptor targeting is almost completely restored. (H) Quantification of the misprojections of Rh6-lacZ-positive R8 axons in wild-type, otduvi mutant and otduvi mutant flies where Otd expression has been restored using the GMR-Gal4 driver.
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pgen.1005303.g005: otd is required for R8 synaptic-layer targeting.Wild-type (A,A’) and otduvi mutant (B,B’) adult optic lobes expressing the R8 specific marker Rh6-lacZ stained with anti-β-galactosidase (green). In wild-type (A,A’) Rh6-lacZ-positive R8 axons terminate in the M3 layer. otduvi mutants (B-B”) display a strong R8 axon misprojection phenotype. R8 axons specifically overshoot to the M6 layer (boxed in B’ and quantified in Fig 5H) while some R8 axons invade neighbouring columns cross-laterally and terminate in abnormal positions (boxed in B”). Several R8 axons terminals can also be seen to stall at more superficial layers and fail to innervate the medulla (double arrows in b”‘). All panels (C-F) show photoreceptor axon projections stained with the 24B10 antibody (red). R8 axons in wild-type (c,c’) and otduvi mutant (D,D’) optic lobes (40% after puparium formation) are visualized using the ato-τ-myc transgene stained with anti-Myc antibody (green). At this early stage of development, in otduvi mutant retina, R8 growth cones fail to stop in the M1 layer and extend specifically to the R7 temporary layer (n = 438 misprojecting axons of 798 R8 axons quantified in the two temporary layers). The staining for ato-τ-Myc is magnified in (C’,D’) and arrows in (D’) indicate misprojecting R8 axons. boss1 mutant (E) and otduvi/boss1 double-mutant (F) retina. Adult optic lobes stained with 24B10 antibody. In (E), residual 24B10 staining in the R7 M6 layer is derived from medulla neurons [44]. (E) boss1 mutant R8 terminate in the R8 recipient layer M3, with only a few R8 targeting to the M6 layer. (F) Most of the otduvi/boss1 double-mutants display a strong R8 mis-projection phenotype in the R7 layer, M6. (G) otduvi mutant flies where Otd expression has been restored specifically in the photoreceptors using the GMRGal4 driver. In this context, staining of the R8 specific marker Rh6-lacZ (green) demonstrates that normal R8 photoreceptor targeting is almost completely restored. (H) Quantification of the misprojections of Rh6-lacZ-positive R8 axons in wild-type, otduvi mutant and otduvi mutant flies where Otd expression has been restored using the GMR-Gal4 driver.

Mentions: These experiments suggest that in the absence of otd, layer-specific targeting of R8 should be affected. To test this hypothesis, we examined the projection pattern of R8 terminals in otduvi animals, using the R8 specific Rh6-lacZ reporter transgene. When examining adult medulla stained for Rh6-lacZ, we found that 59% (n = 503 of 854) of mature R8 terminals fail to stop in the M3 layer and instead terminate in the M6 layer, where R7 terminals are normally found (Fig 5A, 5B’ and 5H). This phenotype can also be detected using the allele otdJA101 [30] combined to the MARCM system [31] (S3 Fig). In this case, as for otduvi, not all R8 axons project ectopically in the M6 layer, suggesting that during R8 synaptic layer-specific projection, another redundant pathway might function in parallel of otd.


Orthodenticle Is Required for the Expression of Principal Recognition Molecules That Control Axon Targeting in the Drosophila Retina.

Mencarelli C, Pichaud F - PLoS Genet. (2015)

otd is required for R8 synaptic-layer targeting.Wild-type (A,A’) and otduvi mutant (B,B’) adult optic lobes expressing the R8 specific marker Rh6-lacZ stained with anti-β-galactosidase (green). In wild-type (A,A’) Rh6-lacZ-positive R8 axons terminate in the M3 layer. otduvi mutants (B-B”) display a strong R8 axon misprojection phenotype. R8 axons specifically overshoot to the M6 layer (boxed in B’ and quantified in Fig 5H) while some R8 axons invade neighbouring columns cross-laterally and terminate in abnormal positions (boxed in B”). Several R8 axons terminals can also be seen to stall at more superficial layers and fail to innervate the medulla (double arrows in b”‘). All panels (C-F) show photoreceptor axon projections stained with the 24B10 antibody (red). R8 axons in wild-type (c,c’) and otduvi mutant (D,D’) optic lobes (40% after puparium formation) are visualized using the ato-τ-myc transgene stained with anti-Myc antibody (green). At this early stage of development, in otduvi mutant retina, R8 growth cones fail to stop in the M1 layer and extend specifically to the R7 temporary layer (n = 438 misprojecting axons of 798 R8 axons quantified in the two temporary layers). The staining for ato-τ-Myc is magnified in (C’,D’) and arrows in (D’) indicate misprojecting R8 axons. boss1 mutant (E) and otduvi/boss1 double-mutant (F) retina. Adult optic lobes stained with 24B10 antibody. In (E), residual 24B10 staining in the R7 M6 layer is derived from medulla neurons [44]. (E) boss1 mutant R8 terminate in the R8 recipient layer M3, with only a few R8 targeting to the M6 layer. (F) Most of the otduvi/boss1 double-mutants display a strong R8 mis-projection phenotype in the R7 layer, M6. (G) otduvi mutant flies where Otd expression has been restored specifically in the photoreceptors using the GMRGal4 driver. In this context, staining of the R8 specific marker Rh6-lacZ (green) demonstrates that normal R8 photoreceptor targeting is almost completely restored. (H) Quantification of the misprojections of Rh6-lacZ-positive R8 axons in wild-type, otduvi mutant and otduvi mutant flies where Otd expression has been restored using the GMR-Gal4 driver.
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Related In: Results  -  Collection

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pgen.1005303.g005: otd is required for R8 synaptic-layer targeting.Wild-type (A,A’) and otduvi mutant (B,B’) adult optic lobes expressing the R8 specific marker Rh6-lacZ stained with anti-β-galactosidase (green). In wild-type (A,A’) Rh6-lacZ-positive R8 axons terminate in the M3 layer. otduvi mutants (B-B”) display a strong R8 axon misprojection phenotype. R8 axons specifically overshoot to the M6 layer (boxed in B’ and quantified in Fig 5H) while some R8 axons invade neighbouring columns cross-laterally and terminate in abnormal positions (boxed in B”). Several R8 axons terminals can also be seen to stall at more superficial layers and fail to innervate the medulla (double arrows in b”‘). All panels (C-F) show photoreceptor axon projections stained with the 24B10 antibody (red). R8 axons in wild-type (c,c’) and otduvi mutant (D,D’) optic lobes (40% after puparium formation) are visualized using the ato-τ-myc transgene stained with anti-Myc antibody (green). At this early stage of development, in otduvi mutant retina, R8 growth cones fail to stop in the M1 layer and extend specifically to the R7 temporary layer (n = 438 misprojecting axons of 798 R8 axons quantified in the two temporary layers). The staining for ato-τ-Myc is magnified in (C’,D’) and arrows in (D’) indicate misprojecting R8 axons. boss1 mutant (E) and otduvi/boss1 double-mutant (F) retina. Adult optic lobes stained with 24B10 antibody. In (E), residual 24B10 staining in the R7 M6 layer is derived from medulla neurons [44]. (E) boss1 mutant R8 terminate in the R8 recipient layer M3, with only a few R8 targeting to the M6 layer. (F) Most of the otduvi/boss1 double-mutants display a strong R8 mis-projection phenotype in the R7 layer, M6. (G) otduvi mutant flies where Otd expression has been restored specifically in the photoreceptors using the GMRGal4 driver. In this context, staining of the R8 specific marker Rh6-lacZ (green) demonstrates that normal R8 photoreceptor targeting is almost completely restored. (H) Quantification of the misprojections of Rh6-lacZ-positive R8 axons in wild-type, otduvi mutant and otduvi mutant flies where Otd expression has been restored using the GMR-Gal4 driver.
Mentions: These experiments suggest that in the absence of otd, layer-specific targeting of R8 should be affected. To test this hypothesis, we examined the projection pattern of R8 terminals in otduvi animals, using the R8 specific Rh6-lacZ reporter transgene. When examining adult medulla stained for Rh6-lacZ, we found that 59% (n = 503 of 854) of mature R8 terminals fail to stop in the M3 layer and instead terminate in the M6 layer, where R7 terminals are normally found (Fig 5A, 5B’ and 5H). This phenotype can also be detected using the allele otdJA101 [30] combined to the MARCM system [31] (S3 Fig). In this case, as for otduvi, not all R8 axons project ectopically in the M6 layer, suggesting that during R8 synaptic layer-specific projection, another redundant pathway might function in parallel of otd.

Bottom Line: Our data indicate that otd function in these photoreceptors is largely mediated by the recognition molecules flamingo (fmi) and golden goal (gogo).In addition, we find that otd regulates synaptic-layer targeting of R8.Our work therefore demonstrates that otd is a main component of the gene regulatory network that regulates synaptic-column and layer targeting in the fly visual system.

View Article: PubMed Central - PubMed

Affiliation: MRC Laboratory for Molecular Cell Biology, University College London, London, United Kingdom.

ABSTRACT
Parallel processing of neuronal inputs relies on assembling neural circuits into distinct synaptic-columns and layers. This is orchestrated by matching recognition molecules between afferent growth cones and target areas. Controlling the expression of these molecules during development is crucial but not well understood. The developing Drosophila visual system is a powerful genetic model for addressing this question. In this model system, the achromatic R1-6 photoreceptors project their axons in the lamina while the R7 and R8 photoreceptors, which are involved in colour detection, project their axons to two distinct synaptic-layers in the medulla. Here we show that the conserved homeodomain transcription factor Orthodenticle (Otd), which in the eye is a main regulator of rhodopsin expression, is also required for R1-6 photoreceptor synaptic-column specific innervation of the lamina. Our data indicate that otd function in these photoreceptors is largely mediated by the recognition molecules flamingo (fmi) and golden goal (gogo). In addition, we find that otd regulates synaptic-layer targeting of R8. We demonstrate that during this process, otd and the R8-specific transcription factor senseless/Gfi1 (sens) function as independent transcriptional inputs that are required for the expression of fmi, gogo and the adhesion molecule capricious (caps), which govern R8 synaptic-layer targeting. Our work therefore demonstrates that otd is a main component of the gene regulatory network that regulates synaptic-column and layer targeting in the fly visual system.

No MeSH data available.


Related in: MedlinePlus