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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 synaptic-column targeting of R1-6 in the lamina.Electron micrographs of lamina cross-sections showing the normal organization of synaptic-columns in a wild-type lamina (A) and the defects in lamina column innervation observed in the case of otd mutant retina (B). Photoreceptor terminals are colored in pink (R), central lamina neurons are labeled ‘L’. Confocal sections of wild-type (C-C’,E,E’) and otd mutant (D,D’,F,F’) lamina at 40% after puparium formation. R1-6 axons are labeled by mCD8::GFP (green in C,D and E,F) and stained for Fmi (C-D’) (red) or NCad (E-F’) (red). (G) Frequency distribution polygon showing the numbers of R1-6 axons terminals innervating each synaptic column in otduvi mutant lamina (black line) and in otduvi mutants where either fmi (red line) or gogo (green line) are expressed using the GMR-Gal4 driver line. Data were gathered from EM micrographs. A Levene's test for the equality of variances, was applied. The variance in the number of axon terminals per cartridge is significantly lower in the otduvi; GMR-Gal4; UAS-fmi and otduvi; GMR-Gal4; UAS-gogo lamina (1.66 and 1.70 respectively) compared to otduv mutant flies (2.83, p<0.05 in both cases). (H) Real-time PCR quantification of caps, gogo, fmi, lar, NCad and InR mRNA normalized to GAPDH mRNA levels comparing wild-type and otd mutant retina at 40% after puparium formation. n = at least three independent mRNA extracts from wild-type and otd-mutant retinas. Error bars represent SEM.
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pgen.1005303.g003: otd is required for synaptic-column targeting of R1-6 in the lamina.Electron micrographs of lamina cross-sections showing the normal organization of synaptic-columns in a wild-type lamina (A) and the defects in lamina column innervation observed in the case of otd mutant retina (B). Photoreceptor terminals are colored in pink (R), central lamina neurons are labeled ‘L’. Confocal sections of wild-type (C-C’,E,E’) and otd mutant (D,D’,F,F’) lamina at 40% after puparium formation. R1-6 axons are labeled by mCD8::GFP (green in C,D and E,F) and stained for Fmi (C-D’) (red) or NCad (E-F’) (red). (G) Frequency distribution polygon showing the numbers of R1-6 axons terminals innervating each synaptic column in otduvi mutant lamina (black line) and in otduvi mutants where either fmi (red line) or gogo (green line) are expressed using the GMR-Gal4 driver line. Data were gathered from EM micrographs. A Levene's test for the equality of variances, was applied. The variance in the number of axon terminals per cartridge is significantly lower in the otduvi; GMR-Gal4; UAS-fmi and otduvi; GMR-Gal4; UAS-gogo lamina (1.66 and 1.70 respectively) compared to otduv mutant flies (2.83, p<0.05 in both cases). (H) Real-time PCR quantification of caps, gogo, fmi, lar, NCad and InR mRNA normalized to GAPDH mRNA levels comparing wild-type and otd mutant retina at 40% after puparium formation. n = at least three independent mRNA extracts from wild-type and otd-mutant retinas. Error bars represent SEM.

Mentions: We first examined the lamina column targeting of otd mutant R1-6 photoreceptors in more detail. To this end, we used electron microscopy to quantify the number of afferent R1-6 photoreceptor neurons that target each lamina column (also referred to as lamina cartridge). In the main part of the retina, outside of the midline of wild-type eyes, six R1-6 afferent axons converge on one synaptic column in the lamina (Fig 1B and 3A). In contrast, we find that in the case of retinae mutant for otd, the number of axon terminals that innervate the lamina columns varies, ranging from 2 and 10 (Fig 3B and 3G). This quantification reveals a failure of the R1-6 axons to innervate their appropriate synaptic-columns, demonstrating that otd is required for axonal targeting of R1-6 in the lamina.


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 synaptic-column targeting of R1-6 in the lamina.Electron micrographs of lamina cross-sections showing the normal organization of synaptic-columns in a wild-type lamina (A) and the defects in lamina column innervation observed in the case of otd mutant retina (B). Photoreceptor terminals are colored in pink (R), central lamina neurons are labeled ‘L’. Confocal sections of wild-type (C-C’,E,E’) and otd mutant (D,D’,F,F’) lamina at 40% after puparium formation. R1-6 axons are labeled by mCD8::GFP (green in C,D and E,F) and stained for Fmi (C-D’) (red) or NCad (E-F’) (red). (G) Frequency distribution polygon showing the numbers of R1-6 axons terminals innervating each synaptic column in otduvi mutant lamina (black line) and in otduvi mutants where either fmi (red line) or gogo (green line) are expressed using the GMR-Gal4 driver line. Data were gathered from EM micrographs. A Levene's test for the equality of variances, was applied. The variance in the number of axon terminals per cartridge is significantly lower in the otduvi; GMR-Gal4; UAS-fmi and otduvi; GMR-Gal4; UAS-gogo lamina (1.66 and 1.70 respectively) compared to otduv mutant flies (2.83, p<0.05 in both cases). (H) Real-time PCR quantification of caps, gogo, fmi, lar, NCad and InR mRNA normalized to GAPDH mRNA levels comparing wild-type and otd mutant retina at 40% after puparium formation. n = at least three independent mRNA extracts from wild-type and otd-mutant retinas. Error bars represent SEM.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4482733&req=5

pgen.1005303.g003: otd is required for synaptic-column targeting of R1-6 in the lamina.Electron micrographs of lamina cross-sections showing the normal organization of synaptic-columns in a wild-type lamina (A) and the defects in lamina column innervation observed in the case of otd mutant retina (B). Photoreceptor terminals are colored in pink (R), central lamina neurons are labeled ‘L’. Confocal sections of wild-type (C-C’,E,E’) and otd mutant (D,D’,F,F’) lamina at 40% after puparium formation. R1-6 axons are labeled by mCD8::GFP (green in C,D and E,F) and stained for Fmi (C-D’) (red) or NCad (E-F’) (red). (G) Frequency distribution polygon showing the numbers of R1-6 axons terminals innervating each synaptic column in otduvi mutant lamina (black line) and in otduvi mutants where either fmi (red line) or gogo (green line) are expressed using the GMR-Gal4 driver line. Data were gathered from EM micrographs. A Levene's test for the equality of variances, was applied. The variance in the number of axon terminals per cartridge is significantly lower in the otduvi; GMR-Gal4; UAS-fmi and otduvi; GMR-Gal4; UAS-gogo lamina (1.66 and 1.70 respectively) compared to otduv mutant flies (2.83, p<0.05 in both cases). (H) Real-time PCR quantification of caps, gogo, fmi, lar, NCad and InR mRNA normalized to GAPDH mRNA levels comparing wild-type and otd mutant retina at 40% after puparium formation. n = at least three independent mRNA extracts from wild-type and otd-mutant retinas. Error bars represent SEM.
Mentions: We first examined the lamina column targeting of otd mutant R1-6 photoreceptors in more detail. To this end, we used electron microscopy to quantify the number of afferent R1-6 photoreceptor neurons that target each lamina column (also referred to as lamina cartridge). In the main part of the retina, outside of the midline of wild-type eyes, six R1-6 afferent axons converge on one synaptic column in the lamina (Fig 1B and 3A). In contrast, we find that in the case of retinae mutant for otd, the number of axon terminals that innervate the lamina columns varies, ranging from 2 and 10 (Fig 3B and 3G). This quantification reveals a failure of the R1-6 axons to innervate their appropriate synaptic-columns, demonstrating that otd is required for axonal targeting of R1-6 in the lamina.

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