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Yki/YAP, Sd/TEAD and Hth/MEIS control tissue specification in the Drosophila eye disc epithelium.

Zhang T, Zhou Q, Pignoni F - PLoS ONE (2011)

Bottom Line: RNAi-mediated inactivation of Yki, or its partner Scalloped (Sd), or increased activity of the upstream negative regulators of Yki cause a dramatic reorganization of the eye disc fate map leading to specification of the entire disc epithelium into retina.On the contrary, constitutive expression of Yki suppresses eye formation in a Sd-dependent fashion.Our results support a critical role for Yki- and its partners Sd and Hth--in shaping the fate map of the eye epithelium independently of its universal role as a regulator of proliferation and survival.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology, Center for Vision Research, and SUNY Eye Institute, SUNY Upstate Medical University, Syracuse, New York, United States of America.

ABSTRACT
During animal development, accurate control of tissue specification and growth are critical to generate organisms of reproducible shape and size. The eye-antennal disc epithelium of Drosophila is a powerful model system to identify the signaling pathway and transcription factors that mediate and coordinate these processes. We show here that the Yorkie (Yki) pathway plays a major role in tissue specification within the developing fly eye disc epithelium at a time when organ primordia and regional identity domains are specified. RNAi-mediated inactivation of Yki, or its partner Scalloped (Sd), or increased activity of the upstream negative regulators of Yki cause a dramatic reorganization of the eye disc fate map leading to specification of the entire disc epithelium into retina. On the contrary, constitutive expression of Yki suppresses eye formation in a Sd-dependent fashion. We also show that knockdown of the transcription factor Homothorax (Hth), known to partner Yki in some developmental contexts, also induces an ectopic retina domain, that Yki and Scalloped regulate Hth expression, and that the gain-of-function activity of Yki is partially dependent on Hth. Our results support a critical role for Yki- and its partners Sd and Hth--in shaping the fate map of the eye epithelium independently of its universal role as a regulator of proliferation and survival.

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Related in: MedlinePlus

Gene silencing in the PE is sufficient to induce the PE–to-DP transformation.A) pnr-Gal4 drives expression in ∼early-mid L2 discs. Top: XY and ZX views of one disc; bottom: ZX of another. Gal4 is expressed in a broad domain within the dorsal PE. B) pnr-Gal4 UAS-ykiRNAi disc stained for Dlg (for cell shape) and Elav (for neurons). Right: confocal XY image of L3 disc with ZX and ZY projections; left: high magnification ZY of the same disc. PE-restricted expression of yki-RNAi transforms the dorsal region of the PE into DP/retina. High magnification panel shows that the transition from transformed to non-transformed region occurs over a few cell diameters. C, D) L3 discs stained in red for (top to bottom) dpp (dpp-lacZ) which marks the transition zone between eye progenitor cells and developing neurons, the RDFs tsh (tsh-lacZ) and Ey which mark eye progenitor cells, and the pan-neural membrane marker 22C10 which highlights differentiating neurons and their axons. Where shown, the membrane marker E-cadherin is in green. C) wt L3 discs show normal expression of dpp-lacZ in the transition zone where morphogenesis of the ommatidial array begins (visible as a depression in the DP of the wt discs, but not so marked in most transformed discs), tsh-lacZ and Ey in eye progenitor cells in the anterior portion of the disc (expression of Ey in the PE layer is also seen), and 22C10 stained neurons projects their axons posteriorly, along the basal side of the DP into the optic stalk and brain (not shown). Asterisk marks an axonal fascicle outside the eye disc (Bolwig's nerve). D) sd-RNAi L3 discs show mirror image duplications of each expression domain in two thicker, DP-like cell layers. The domains of dpp-lacZ expression are offset, indicating that, in this disc, neurogenesis in one layer lags behind the other layer. This was not always the case.
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pone-0022278-g002: Gene silencing in the PE is sufficient to induce the PE–to-DP transformation.A) pnr-Gal4 drives expression in ∼early-mid L2 discs. Top: XY and ZX views of one disc; bottom: ZX of another. Gal4 is expressed in a broad domain within the dorsal PE. B) pnr-Gal4 UAS-ykiRNAi disc stained for Dlg (for cell shape) and Elav (for neurons). Right: confocal XY image of L3 disc with ZX and ZY projections; left: high magnification ZY of the same disc. PE-restricted expression of yki-RNAi transforms the dorsal region of the PE into DP/retina. High magnification panel shows that the transition from transformed to non-transformed region occurs over a few cell diameters. C, D) L3 discs stained in red for (top to bottom) dpp (dpp-lacZ) which marks the transition zone between eye progenitor cells and developing neurons, the RDFs tsh (tsh-lacZ) and Ey which mark eye progenitor cells, and the pan-neural membrane marker 22C10 which highlights differentiating neurons and their axons. Where shown, the membrane marker E-cadherin is in green. C) wt L3 discs show normal expression of dpp-lacZ in the transition zone where morphogenesis of the ommatidial array begins (visible as a depression in the DP of the wt discs, but not so marked in most transformed discs), tsh-lacZ and Ey in eye progenitor cells in the anterior portion of the disc (expression of Ey in the PE layer is also seen), and 22C10 stained neurons projects their axons posteriorly, along the basal side of the DP into the optic stalk and brain (not shown). Asterisk marks an axonal fascicle outside the eye disc (Bolwig's nerve). D) sd-RNAi L3 discs show mirror image duplications of each expression domain in two thicker, DP-like cell layers. The domains of dpp-lacZ expression are offset, indicating that, in this disc, neurogenesis in one layer lags behind the other layer. This was not always the case.

Mentions: Since the ey-Flip; Act>IC>Gal4 driver drives expression in both PE ad DP cell layers, and yki appears to function in a non-cell-autonomous fashion, we sought to investigate whether the transformation phenotype indeed resulted from the loss of Yki function within the PE or involved more complex long range effects. We, therefore, used the PE-specific Gal4 line pnr-Gal4 [19] to drive either 2 copies of UAS-GFP or one copy of a UAS-yki-RNAi transgene. In control discs, GFP expression was exclusively restricted to the dorsal side of the PE cell layer throughout the larval stages (Fig. 2A, and not shown). At the L2 stage (when gene function is required, as shown below), GFP was detected in a large dorsal section of the PE cell layer over the entire eye-antennal disc (Fig. 2A). In pnr-Gal4 yki-RNAi discs, the dorsal half of the PE epithelium became columnar and displayed a developing ommatidial array by the L3 stage (Fig. 2B). As shown in the magnified panel in Fig. 2B, the transition from the columnar, transformed PE cells to the unchanged squamous PE cells occur sharply within a few cell diameters. Unfortunately, we cannot use this genetic background to explore whether signs of non-cell-autonomy are present because the co-expressed GFP is no longer detected by the stage at which cell fate can be most readily assessed (late L3). This is not unexpected, since the pnr-Gal4 is a PE-specific driver, hence its expression is down-regulated over time as the transformed PE-cells are locked into a DP fate.


Yki/YAP, Sd/TEAD and Hth/MEIS control tissue specification in the Drosophila eye disc epithelium.

Zhang T, Zhou Q, Pignoni F - PLoS ONE (2011)

Gene silencing in the PE is sufficient to induce the PE–to-DP transformation.A) pnr-Gal4 drives expression in ∼early-mid L2 discs. Top: XY and ZX views of one disc; bottom: ZX of another. Gal4 is expressed in a broad domain within the dorsal PE. B) pnr-Gal4 UAS-ykiRNAi disc stained for Dlg (for cell shape) and Elav (for neurons). Right: confocal XY image of L3 disc with ZX and ZY projections; left: high magnification ZY of the same disc. PE-restricted expression of yki-RNAi transforms the dorsal region of the PE into DP/retina. High magnification panel shows that the transition from transformed to non-transformed region occurs over a few cell diameters. C, D) L3 discs stained in red for (top to bottom) dpp (dpp-lacZ) which marks the transition zone between eye progenitor cells and developing neurons, the RDFs tsh (tsh-lacZ) and Ey which mark eye progenitor cells, and the pan-neural membrane marker 22C10 which highlights differentiating neurons and their axons. Where shown, the membrane marker E-cadherin is in green. C) wt L3 discs show normal expression of dpp-lacZ in the transition zone where morphogenesis of the ommatidial array begins (visible as a depression in the DP of the wt discs, but not so marked in most transformed discs), tsh-lacZ and Ey in eye progenitor cells in the anterior portion of the disc (expression of Ey in the PE layer is also seen), and 22C10 stained neurons projects their axons posteriorly, along the basal side of the DP into the optic stalk and brain (not shown). Asterisk marks an axonal fascicle outside the eye disc (Bolwig's nerve). D) sd-RNAi L3 discs show mirror image duplications of each expression domain in two thicker, DP-like cell layers. The domains of dpp-lacZ expression are offset, indicating that, in this disc, neurogenesis in one layer lags behind the other layer. This was not always the case.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3139632&req=5

pone-0022278-g002: Gene silencing in the PE is sufficient to induce the PE–to-DP transformation.A) pnr-Gal4 drives expression in ∼early-mid L2 discs. Top: XY and ZX views of one disc; bottom: ZX of another. Gal4 is expressed in a broad domain within the dorsal PE. B) pnr-Gal4 UAS-ykiRNAi disc stained for Dlg (for cell shape) and Elav (for neurons). Right: confocal XY image of L3 disc with ZX and ZY projections; left: high magnification ZY of the same disc. PE-restricted expression of yki-RNAi transforms the dorsal region of the PE into DP/retina. High magnification panel shows that the transition from transformed to non-transformed region occurs over a few cell diameters. C, D) L3 discs stained in red for (top to bottom) dpp (dpp-lacZ) which marks the transition zone between eye progenitor cells and developing neurons, the RDFs tsh (tsh-lacZ) and Ey which mark eye progenitor cells, and the pan-neural membrane marker 22C10 which highlights differentiating neurons and their axons. Where shown, the membrane marker E-cadherin is in green. C) wt L3 discs show normal expression of dpp-lacZ in the transition zone where morphogenesis of the ommatidial array begins (visible as a depression in the DP of the wt discs, but not so marked in most transformed discs), tsh-lacZ and Ey in eye progenitor cells in the anterior portion of the disc (expression of Ey in the PE layer is also seen), and 22C10 stained neurons projects their axons posteriorly, along the basal side of the DP into the optic stalk and brain (not shown). Asterisk marks an axonal fascicle outside the eye disc (Bolwig's nerve). D) sd-RNAi L3 discs show mirror image duplications of each expression domain in two thicker, DP-like cell layers. The domains of dpp-lacZ expression are offset, indicating that, in this disc, neurogenesis in one layer lags behind the other layer. This was not always the case.
Mentions: Since the ey-Flip; Act>IC>Gal4 driver drives expression in both PE ad DP cell layers, and yki appears to function in a non-cell-autonomous fashion, we sought to investigate whether the transformation phenotype indeed resulted from the loss of Yki function within the PE or involved more complex long range effects. We, therefore, used the PE-specific Gal4 line pnr-Gal4 [19] to drive either 2 copies of UAS-GFP or one copy of a UAS-yki-RNAi transgene. In control discs, GFP expression was exclusively restricted to the dorsal side of the PE cell layer throughout the larval stages (Fig. 2A, and not shown). At the L2 stage (when gene function is required, as shown below), GFP was detected in a large dorsal section of the PE cell layer over the entire eye-antennal disc (Fig. 2A). In pnr-Gal4 yki-RNAi discs, the dorsal half of the PE epithelium became columnar and displayed a developing ommatidial array by the L3 stage (Fig. 2B). As shown in the magnified panel in Fig. 2B, the transition from the columnar, transformed PE cells to the unchanged squamous PE cells occur sharply within a few cell diameters. Unfortunately, we cannot use this genetic background to explore whether signs of non-cell-autonomy are present because the co-expressed GFP is no longer detected by the stage at which cell fate can be most readily assessed (late L3). This is not unexpected, since the pnr-Gal4 is a PE-specific driver, hence its expression is down-regulated over time as the transformed PE-cells are locked into a DP fate.

Bottom Line: RNAi-mediated inactivation of Yki, or its partner Scalloped (Sd), or increased activity of the upstream negative regulators of Yki cause a dramatic reorganization of the eye disc fate map leading to specification of the entire disc epithelium into retina.On the contrary, constitutive expression of Yki suppresses eye formation in a Sd-dependent fashion.Our results support a critical role for Yki- and its partners Sd and Hth--in shaping the fate map of the eye epithelium independently of its universal role as a regulator of proliferation and survival.

View Article: PubMed Central - PubMed

Affiliation: Department of Ophthalmology, Center for Vision Research, and SUNY Eye Institute, SUNY Upstate Medical University, Syracuse, New York, United States of America.

ABSTRACT
During animal development, accurate control of tissue specification and growth are critical to generate organisms of reproducible shape and size. The eye-antennal disc epithelium of Drosophila is a powerful model system to identify the signaling pathway and transcription factors that mediate and coordinate these processes. We show here that the Yorkie (Yki) pathway plays a major role in tissue specification within the developing fly eye disc epithelium at a time when organ primordia and regional identity domains are specified. RNAi-mediated inactivation of Yki, or its partner Scalloped (Sd), or increased activity of the upstream negative regulators of Yki cause a dramatic reorganization of the eye disc fate map leading to specification of the entire disc epithelium into retina. On the contrary, constitutive expression of Yki suppresses eye formation in a Sd-dependent fashion. We also show that knockdown of the transcription factor Homothorax (Hth), known to partner Yki in some developmental contexts, also induces an ectopic retina domain, that Yki and Scalloped regulate Hth expression, and that the gain-of-function activity of Yki is partially dependent on Hth. Our results support a critical role for Yki- and its partners Sd and Hth--in shaping the fate map of the eye epithelium independently of its universal role as a regulator of proliferation and survival.

Show MeSH
Related in: MedlinePlus