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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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Optix misexpression disrupts neuroepithelial organisation. (A-C) Posterior cross-sections of late third instar brain lobes. Cells are outlined by Dlg (red) and Ed staining labels apical cell surfaces (green), indicating the apico-basal axis of the tissue with respect to the brain. Optix misexpression using OptixGAL4 severely disrupts neuroepithelial architecture. Multilayering of neuroepithelial cells (B) and rosette formation (C, yellow arrowheads) were observed, in contrast to the regular pseudostratified structure of wild type outer proliferation centre (OPC) neuroepithelium (A). (D, E)Optix misexpression alters Dlg (red) levels and localisation. Higher levels of apical Dlg are observed when Optix is misexpressed (yellow arrowhead in E). (F, F’)Optix misexpression clones were induced in the neuroepithelium. These clones form rosettes in which Dlg accumulates apically (yellow arrowhead). Clones labelled with mCD8-GFP (blue), cells stained for Dlg (red) and Dpn (green). (D-F) 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 8: Optix misexpression disrupts neuroepithelial organisation. (A-C) Posterior cross-sections of late third instar brain lobes. Cells are outlined by Dlg (red) and Ed staining labels apical cell surfaces (green), indicating the apico-basal axis of the tissue with respect to the brain. Optix misexpression using OptixGAL4 severely disrupts neuroepithelial architecture. Multilayering of neuroepithelial cells (B) and rosette formation (C, yellow arrowheads) were observed, in contrast to the regular pseudostratified structure of wild type outer proliferation centre (OPC) neuroepithelium (A). (D, E)Optix misexpression alters Dlg (red) levels and localisation. Higher levels of apical Dlg are observed when Optix is misexpressed (yellow arrowhead in E). (F, F’)Optix misexpression clones were induced in the neuroepithelium. These clones form rosettes in which Dlg accumulates apically (yellow arrowhead). Clones labelled with mCD8-GFP (blue), cells stained for Dlg (red) and Dpn (green). (D-F) 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: Removing Optix from cells surrounded by wild type Optix-expressing neighbours results in basal extrusion and cell sorting. To explore the effects of increased Optix expression on neuroepithelial cell behaviour, we overexpressed Optix in the neuroepithelium. Optix was misexpressed using a temperature-sensitive driver combination either throughout the OPC neuroepithelium (with c855aGAL4) or in the neuroepithelial domain where it is usually expressed (with OptixGAL4). Optix misexpression using both drivers induced multi-layering of the OPC neuroepithelium (Figure 8B; Additional file 5), compared to its wild type pseudostratified architecture [52,83]. Neuroepithelial cells rounded up and lost their columnar epithelial shape. Apical polarity markers such as Echinoid were lost from these multilayered epithelia (Figure 8B). In some instances Optix misexpression caused the arms of the neuroepithelium to curve and round up on themselves. This resulted in the formation of rosette-like structures, with the apical centres of cells clustered together in the centre, as indicated by Echinoid localisation (Figure 8C). Thus Optix misexpression resulted in a loss of columnar neuroepithelial apico-basal polarity.


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

Gold KS, Brand AH - Neural Dev (2014)

Optix misexpression disrupts neuroepithelial organisation. (A-C) Posterior cross-sections of late third instar brain lobes. Cells are outlined by Dlg (red) and Ed staining labels apical cell surfaces (green), indicating the apico-basal axis of the tissue with respect to the brain. Optix misexpression using OptixGAL4 severely disrupts neuroepithelial architecture. Multilayering of neuroepithelial cells (B) and rosette formation (C, yellow arrowheads) were observed, in contrast to the regular pseudostratified structure of wild type outer proliferation centre (OPC) neuroepithelium (A). (D, E)Optix misexpression alters Dlg (red) levels and localisation. Higher levels of apical Dlg are observed when Optix is misexpressed (yellow arrowhead in E). (F, F’)Optix misexpression clones were induced in the neuroepithelium. These clones form rosettes in which Dlg accumulates apically (yellow arrowhead). Clones labelled with mCD8-GFP (blue), cells stained for Dlg (red) and Dpn (green). (D-F) 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

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Figure 8: Optix misexpression disrupts neuroepithelial organisation. (A-C) Posterior cross-sections of late third instar brain lobes. Cells are outlined by Dlg (red) and Ed staining labels apical cell surfaces (green), indicating the apico-basal axis of the tissue with respect to the brain. Optix misexpression using OptixGAL4 severely disrupts neuroepithelial architecture. Multilayering of neuroepithelial cells (B) and rosette formation (C, yellow arrowheads) were observed, in contrast to the regular pseudostratified structure of wild type outer proliferation centre (OPC) neuroepithelium (A). (D, E)Optix misexpression alters Dlg (red) levels and localisation. Higher levels of apical Dlg are observed when Optix is misexpressed (yellow arrowhead in E). (F, F’)Optix misexpression clones were induced in the neuroepithelium. These clones form rosettes in which Dlg accumulates apically (yellow arrowhead). Clones labelled with mCD8-GFP (blue), cells stained for Dlg (red) and Dpn (green). (D-F) 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: Removing Optix from cells surrounded by wild type Optix-expressing neighbours results in basal extrusion and cell sorting. To explore the effects of increased Optix expression on neuroepithelial cell behaviour, we overexpressed Optix in the neuroepithelium. Optix was misexpressed using a temperature-sensitive driver combination either throughout the OPC neuroepithelium (with c855aGAL4) or in the neuroepithelial domain where it is usually expressed (with OptixGAL4). Optix misexpression using both drivers induced multi-layering of the OPC neuroepithelium (Figure 8B; Additional file 5), compared to its wild type pseudostratified architecture [52,83]. Neuroepithelial cells rounded up and lost their columnar epithelial shape. Apical polarity markers such as Echinoid were lost from these multilayered epithelia (Figure 8B). In some instances Optix misexpression caused the arms of the neuroepithelium to curve and round up on themselves. This resulted in the formation of rosette-like structures, with the apical centres of cells clustered together in the centre, as indicated by Echinoid localisation (Figure 8C). Thus Optix misexpression resulted in a loss of columnar neuroepithelial apico-basal polarity.

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