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Optix defines a neuroepithelial compartment in the optic lobe of the Drosophila brain.

Gold KS, Brand AH - Neural Dev (2014)

Bottom Line: Neuroepithelia are regionalised by the expression of transcription factors and signalling molecules, resulting in the formation of distinct developmental, and ultimately functional, domains.Six3 and Six6 are required for mammalian eye and forebrain development, and mutations in humans are associated with severe eye and brain malformation.Our findings provide insight into the spatial patterning of a complex region of the brain, and suggest an evolutionarily conserved principle of visual system development.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Gurdon Institute and Department of Physiology, Development & Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK. a.brand@gurdon.cam.ac.uk.

ABSTRACT

Background: During early brain development, the organisation of neural progenitors into a neuroepithelial sheet maintains tissue integrity during growth. Neuroepithelial cohesion and patterning is essential for orderly proliferation and neural fate specification. Neuroepithelia are regionalised by the expression of transcription factors and signalling molecules, resulting in the formation of distinct developmental, and ultimately functional, domains.

Results: We have discovered that the Six3/6 family orthologue Optix is an essential regulator of neuroepithelial maintenance and patterning in the Drosophila brain. Six3 and Six6 are required for mammalian eye and forebrain development, and mutations in humans are associated with severe eye and brain malformation. In Drosophila, Optix is expressed in a sharply defined region of the larval optic lobe, and its expression is reciprocal to that of the transcription factor Vsx1. Optix gain- and loss-of-function affects neuroepithelial adhesion, integrity and polarity. We find restricted cell lineage boundaries that correspond to transcription factor expression domains.

Conclusion: We propose that the optic lobe is compartmentalised by expression of Optix and Vsx1. Our findings provide insight into the spatial patterning of a complex region of the brain, and suggest an evolutionarily conserved principle of visual system development.

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Loss of adhesion leads to ectopic neuroepithelial rosette formation. (A-C’) Cell death in Optix1  mutant MARCM clones was rescued by expression of p35, which inhibits apoptosis. Clones are labelled with mCD8-GFP (green), Echinoid labels adherens junctions (Ed, red), cells are outlined by Dlg (blue). (A-A’) Control clones expressing p35 remain in the neuroepithelium. (B-C’)Optix1 mutant clones expressing p35 form ectopic neuroepithelial rosettes in the underlying medulla cortex. (D-F) Null mutant clones for DE-Cadherin (shg1) delaminate basally from the neuroepithelium to form rosettes below in the underlying medulla cortex (E, F), in contrast to FRTG13 control clones. (D) Clones are labelled with mCD8-GFP (green), PatJ labels adherens junctions (PatJ, red), cells outlined by Dlg (blue). (G-I) Apically localised proteins cluster at the centre of the neuroepithelial rosettes formed by rescued Optix1; UASp35 clones. (G-H) Clones are labelled with mCD8-GFP (green), DE-Cadherin labels adherens junctions (DE-Cad, blue), cells outlined by Phalloidin (F-Actin, red). (I) Clone is labelled with mCD8-GFP (green), cells outlined by Dlg (blue), aPKC is an apically localised protein (aPKC, red). (A-I) Posterior cross-sections are shown in all images. The apico-basal axis of the neuroepithelium is oriented vertically in each image, with the apical surface at the top and the basal surface at the bottom.
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Figure 7: Loss of adhesion leads to ectopic neuroepithelial rosette formation. (A-C’) Cell death in Optix1 mutant MARCM clones was rescued by expression of p35, which inhibits apoptosis. Clones are labelled with mCD8-GFP (green), Echinoid labels adherens junctions (Ed, red), cells are outlined by Dlg (blue). (A-A’) Control clones expressing p35 remain in the neuroepithelium. (B-C’)Optix1 mutant clones expressing p35 form ectopic neuroepithelial rosettes in the underlying medulla cortex. (D-F) Null mutant clones for DE-Cadherin (shg1) delaminate basally from the neuroepithelium to form rosettes below in the underlying medulla cortex (E, F), in contrast to FRTG13 control clones. (D) Clones are labelled with mCD8-GFP (green), PatJ labels adherens junctions (PatJ, red), cells outlined by Dlg (blue). (G-I) Apically localised proteins cluster at the centre of the neuroepithelial rosettes formed by rescued Optix1; UASp35 clones. (G-H) Clones are labelled with mCD8-GFP (green), DE-Cadherin labels adherens junctions (DE-Cad, blue), cells outlined by Phalloidin (F-Actin, red). (I) Clone is labelled with mCD8-GFP (green), cells outlined by Dlg (blue), aPKC is an apically localised protein (aPKC, red). (A-I) Posterior cross-sections are shown in all images. The apico-basal axis of the neuroepithelium is oriented vertically in each image, with the apical surface at the top and the basal surface at the bottom.

Mentions: It was not clear whether the cell death detected in Optix mutant clones was a result of basal extrusion from the neuroepithelium, or whether these cells were extruded because they were undergoing apoptosis. In order to ascertain this, we rescued Optix mutant clones from cell death with baculovirus P35. P35 impairs apical caspase function and inhibits the pro-apoptotic enzyme cascade [75]. Rescuing cell death did not prevent the basal extrusion of Optix mutant clones. Instead, the rescued Optix1; UASp35 mutant cells sort away from the surrounding wild type neuroepithelium (Figure 7B-C) and form ectopic neuroepithelial rosettes in the underlying differentiated cell layer of the medulla cortex (Figure 7C, 7H, 7I). Apically localised proteins and components of adherens junctions, such as Echinoid [76] and DE-Cadherin [77-81], are clustered in the centre of these rosettes (yellow arrowheads, Figure 7B-C). In contrast, control clones expressing p35 remain within the neuroepithelium and do not form rosettes (Figure 7A,G). These results indicated that extrusion of Optix mutant cells from the neuroepithelium was not a consequence of cell death, as it occurred even when apoptosis was blocked. We therefore concluded that Optix is selectively required for the maintenance of neuroepithelial adhesion and cell survival, within its own domain of expression. This reinforces the notion that Optix expression serves to define a neuroepithelial compartment.


Optix defines a neuroepithelial compartment in the optic lobe of the Drosophila brain.

Gold KS, Brand AH - Neural Dev (2014)

Loss of adhesion leads to ectopic neuroepithelial rosette formation. (A-C’) Cell death in Optix1  mutant MARCM clones was rescued by expression of p35, which inhibits apoptosis. Clones are labelled with mCD8-GFP (green), Echinoid labels adherens junctions (Ed, red), cells are outlined by Dlg (blue). (A-A’) Control clones expressing p35 remain in the neuroepithelium. (B-C’)Optix1 mutant clones expressing p35 form ectopic neuroepithelial rosettes in the underlying medulla cortex. (D-F) Null mutant clones for DE-Cadherin (shg1) delaminate basally from the neuroepithelium to form rosettes below in the underlying medulla cortex (E, F), in contrast to FRTG13 control clones. (D) Clones are labelled with mCD8-GFP (green), PatJ labels adherens junctions (PatJ, red), cells outlined by Dlg (blue). (G-I) Apically localised proteins cluster at the centre of the neuroepithelial rosettes formed by rescued Optix1; UASp35 clones. (G-H) Clones are labelled with mCD8-GFP (green), DE-Cadherin labels adherens junctions (DE-Cad, blue), cells outlined by Phalloidin (F-Actin, red). (I) Clone is labelled with mCD8-GFP (green), cells outlined by Dlg (blue), aPKC is an apically localised protein (aPKC, red). (A-I) Posterior cross-sections are shown in all images. The apico-basal axis of the neuroepithelium is oriented vertically in each image, with the apical surface at the top and the basal surface at the bottom.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4127074&req=5

Figure 7: Loss of adhesion leads to ectopic neuroepithelial rosette formation. (A-C’) Cell death in Optix1 mutant MARCM clones was rescued by expression of p35, which inhibits apoptosis. Clones are labelled with mCD8-GFP (green), Echinoid labels adherens junctions (Ed, red), cells are outlined by Dlg (blue). (A-A’) Control clones expressing p35 remain in the neuroepithelium. (B-C’)Optix1 mutant clones expressing p35 form ectopic neuroepithelial rosettes in the underlying medulla cortex. (D-F) Null mutant clones for DE-Cadherin (shg1) delaminate basally from the neuroepithelium to form rosettes below in the underlying medulla cortex (E, F), in contrast to FRTG13 control clones. (D) Clones are labelled with mCD8-GFP (green), PatJ labels adherens junctions (PatJ, red), cells outlined by Dlg (blue). (G-I) Apically localised proteins cluster at the centre of the neuroepithelial rosettes formed by rescued Optix1; UASp35 clones. (G-H) Clones are labelled with mCD8-GFP (green), DE-Cadherin labels adherens junctions (DE-Cad, blue), cells outlined by Phalloidin (F-Actin, red). (I) Clone is labelled with mCD8-GFP (green), cells outlined by Dlg (blue), aPKC is an apically localised protein (aPKC, red). (A-I) Posterior cross-sections are shown in all images. The apico-basal axis of the neuroepithelium is oriented vertically in each image, with the apical surface at the top and the basal surface at the bottom.
Mentions: It was not clear whether the cell death detected in Optix mutant clones was a result of basal extrusion from the neuroepithelium, or whether these cells were extruded because they were undergoing apoptosis. In order to ascertain this, we rescued Optix mutant clones from cell death with baculovirus P35. P35 impairs apical caspase function and inhibits the pro-apoptotic enzyme cascade [75]. Rescuing cell death did not prevent the basal extrusion of Optix mutant clones. Instead, the rescued Optix1; UASp35 mutant cells sort away from the surrounding wild type neuroepithelium (Figure 7B-C) and form ectopic neuroepithelial rosettes in the underlying differentiated cell layer of the medulla cortex (Figure 7C, 7H, 7I). Apically localised proteins and components of adherens junctions, such as Echinoid [76] and DE-Cadherin [77-81], are clustered in the centre of these rosettes (yellow arrowheads, Figure 7B-C). In contrast, control clones expressing p35 remain within the neuroepithelium and do not form rosettes (Figure 7A,G). These results indicated that extrusion of Optix mutant cells from the neuroepithelium was not a consequence of cell death, as it occurred even when apoptosis was blocked. We therefore concluded that Optix is selectively required for the maintenance of neuroepithelial adhesion and cell survival, within its own domain of expression. This reinforces the notion that Optix expression serves to define a neuroepithelial compartment.

Bottom Line: Neuroepithelia are regionalised by the expression of transcription factors and signalling molecules, resulting in the formation of distinct developmental, and ultimately functional, domains.Six3 and Six6 are required for mammalian eye and forebrain development, and mutations in humans are associated with severe eye and brain malformation.Our findings provide insight into the spatial patterning of a complex region of the brain, and suggest an evolutionarily conserved principle of visual system development.

View Article: PubMed Central - HTML - PubMed

Affiliation: The Gurdon Institute and Department of Physiology, Development & Neuroscience, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK. a.brand@gurdon.cam.ac.uk.

ABSTRACT

Background: During early brain development, the organisation of neural progenitors into a neuroepithelial sheet maintains tissue integrity during growth. Neuroepithelial cohesion and patterning is essential for orderly proliferation and neural fate specification. Neuroepithelia are regionalised by the expression of transcription factors and signalling molecules, resulting in the formation of distinct developmental, and ultimately functional, domains.

Results: We have discovered that the Six3/6 family orthologue Optix is an essential regulator of neuroepithelial maintenance and patterning in the Drosophila brain. Six3 and Six6 are required for mammalian eye and forebrain development, and mutations in humans are associated with severe eye and brain malformation. In Drosophila, Optix is expressed in a sharply defined region of the larval optic lobe, and its expression is reciprocal to that of the transcription factor Vsx1. Optix gain- and loss-of-function affects neuroepithelial adhesion, integrity and polarity. We find restricted cell lineage boundaries that correspond to transcription factor expression domains.

Conclusion: We propose that the optic lobe is compartmentalised by expression of Optix and Vsx1. Our findings provide insight into the spatial patterning of a complex region of the brain, and suggest an evolutionarily conserved principle of visual system development.

Show MeSH
Related in: MedlinePlus