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Scaling the Drosophila Wing: TOR-Dependent Target Gene Access by the Hippo Pathway Transducer Yorkie.

Parker J, Struhl G - PLoS Biol. (2015)

Bottom Line: Here, we show that the TOR pathway regulates Yki by a separate and novel mechanism in the Drosophila wing.Instead of controlling Yki nuclear access, TOR signaling governs Yki action after it reaches the nucleus by allowing it to gain access to its target genes.When TOR activity is inhibited, Yki accumulates in the nucleus but is sequestered from its normal growth-promoting target genes--a phenomenon we term "nuclear seclusion." Hence, we posit that in addition to its well-known role in stimulating cellular metabolism in response to nutrients, TOR also promotes wing growth by liberating Yki from nuclear seclusion, a parallel pathway that we propose contributes to the scaling of wing size with nutrient availability.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics and Development, Columbia University, New York, New York, United States of America; Division of Biology, Imperial College London, London, United Kingdom.

ABSTRACT
Organ growth is controlled by patterning signals that operate locally (e.g., Wingless/Ints [Wnts], Bone Morphogenetic Proteins [BMPs], and Hedgehogs [Hhs]) and scaled by nutrient-dependent signals that act systemically (e.g., Insulin-like peptides [ILPs] transduced by the Target of Rapamycin [TOR] pathway). How cells integrate these distinct inputs to generate organs of the appropriate size and shape is largely unknown. The transcriptional coactivator Yorkie (Yki, a YES-Associated Protein, or YAP) acts downstream of patterning morphogens and other tissue-intrinsic signals to promote organ growth. Yki activity is regulated primarily by the Warts/Hippo (Wts/Hpo) tumour suppressor pathway, which impedes nuclear access of Yki by a cytoplasmic tethering mechanism. Here, we show that the TOR pathway regulates Yki by a separate and novel mechanism in the Drosophila wing. Instead of controlling Yki nuclear access, TOR signaling governs Yki action after it reaches the nucleus by allowing it to gain access to its target genes. When TOR activity is inhibited, Yki accumulates in the nucleus but is sequestered from its normal growth-promoting target genes--a phenomenon we term "nuclear seclusion." Hence, we posit that in addition to its well-known role in stimulating cellular metabolism in response to nutrients, TOR also promotes wing growth by liberating Yki from nuclear seclusion, a parallel pathway that we propose contributes to the scaling of wing size with nutrient availability.

No MeSH data available.


Related in: MedlinePlus

TOR inhibition increases Yki nuclear accumulation.(A,C,D) Wing discs expressing GFP-NLS in a stripe of cells under dpp.Gal4 control that either do (C,D, experimental), or do not (A, negative control), coexpress TorTED, TSC1, and TSC2. (B) Wing disc with wtsX1 clones (positive control), marked black by the absence of GFP. Discs are imaged at the level of nuclei and labelled for Yki (red), GFP (green), and DNA (Hoechst, blue). Coexpression of TorTED, TSC1, and TSC2 (C,D), like the loss of Wts (B), causes enhanced nuclear accumulation of Yki, apparent at this plane of focus as increased signal at low magnification (B,C) and by coincidence of the Yki and GFP-NLS signals at high magnification (D, e.g., arrowhead).
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pbio.1002274.g003: TOR inhibition increases Yki nuclear accumulation.(A,C,D) Wing discs expressing GFP-NLS in a stripe of cells under dpp.Gal4 control that either do (C,D, experimental), or do not (A, negative control), coexpress TorTED, TSC1, and TSC2. (B) Wing disc with wtsX1 clones (positive control), marked black by the absence of GFP. Discs are imaged at the level of nuclei and labelled for Yki (red), GFP (green), and DNA (Hoechst, blue). Coexpression of TorTED, TSC1, and TSC2 (C,D), like the loss of Wts (B), causes enhanced nuclear accumulation of Yki, apparent at this plane of focus as increased signal at low magnification (B,C) and by coincidence of the Yki and GFP-NLS signals at high magnification (D, e.g., arrowhead).

Mentions: If Yki depends on, but does not activate, the InR/TOR pathway to promote growth, an alternative explanation is that the InR/TOR pathway acts in parallel to or upstream of Yki. Yki activity depends in large part on phosphorylation by Wts, which causes Yki to be sequestered in the cytosol, reducing its access to the nucleus [15–17]. Yki normally appears predominantly cytoplasmic in the developing wing (Fig 3A), consistent with its essential, but tonic, activity in sustaining wing growth. However, upon Wts inactivation, Yki accumulates in the nucleus and inappropriately up-regulates transcription of its growth-promoting target genes, causing pronounced tissue hyperplasia [15–17] (Fig 3B). Hence, inhibiting TOR activity might countermand the overgrowth phenotype caused by loss of Wts activity by compromising nuclear access of unphosphorylated Yki. In preparing to test this possibility, we were surprised to discover that reducing TOR activity has the opposite effect on Yki localization: instead of restricting nuclear access, it causes a dramatic increase in nuclear Yki, even as it blocks Yki-dependent growth.


Scaling the Drosophila Wing: TOR-Dependent Target Gene Access by the Hippo Pathway Transducer Yorkie.

Parker J, Struhl G - PLoS Biol. (2015)

TOR inhibition increases Yki nuclear accumulation.(A,C,D) Wing discs expressing GFP-NLS in a stripe of cells under dpp.Gal4 control that either do (C,D, experimental), or do not (A, negative control), coexpress TorTED, TSC1, and TSC2. (B) Wing disc with wtsX1 clones (positive control), marked black by the absence of GFP. Discs are imaged at the level of nuclei and labelled for Yki (red), GFP (green), and DNA (Hoechst, blue). Coexpression of TorTED, TSC1, and TSC2 (C,D), like the loss of Wts (B), causes enhanced nuclear accumulation of Yki, apparent at this plane of focus as increased signal at low magnification (B,C) and by coincidence of the Yki and GFP-NLS signals at high magnification (D, e.g., arrowhead).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4608745&req=5

pbio.1002274.g003: TOR inhibition increases Yki nuclear accumulation.(A,C,D) Wing discs expressing GFP-NLS in a stripe of cells under dpp.Gal4 control that either do (C,D, experimental), or do not (A, negative control), coexpress TorTED, TSC1, and TSC2. (B) Wing disc with wtsX1 clones (positive control), marked black by the absence of GFP. Discs are imaged at the level of nuclei and labelled for Yki (red), GFP (green), and DNA (Hoechst, blue). Coexpression of TorTED, TSC1, and TSC2 (C,D), like the loss of Wts (B), causes enhanced nuclear accumulation of Yki, apparent at this plane of focus as increased signal at low magnification (B,C) and by coincidence of the Yki and GFP-NLS signals at high magnification (D, e.g., arrowhead).
Mentions: If Yki depends on, but does not activate, the InR/TOR pathway to promote growth, an alternative explanation is that the InR/TOR pathway acts in parallel to or upstream of Yki. Yki activity depends in large part on phosphorylation by Wts, which causes Yki to be sequestered in the cytosol, reducing its access to the nucleus [15–17]. Yki normally appears predominantly cytoplasmic in the developing wing (Fig 3A), consistent with its essential, but tonic, activity in sustaining wing growth. However, upon Wts inactivation, Yki accumulates in the nucleus and inappropriately up-regulates transcription of its growth-promoting target genes, causing pronounced tissue hyperplasia [15–17] (Fig 3B). Hence, inhibiting TOR activity might countermand the overgrowth phenotype caused by loss of Wts activity by compromising nuclear access of unphosphorylated Yki. In preparing to test this possibility, we were surprised to discover that reducing TOR activity has the opposite effect on Yki localization: instead of restricting nuclear access, it causes a dramatic increase in nuclear Yki, even as it blocks Yki-dependent growth.

Bottom Line: Here, we show that the TOR pathway regulates Yki by a separate and novel mechanism in the Drosophila wing.Instead of controlling Yki nuclear access, TOR signaling governs Yki action after it reaches the nucleus by allowing it to gain access to its target genes.When TOR activity is inhibited, Yki accumulates in the nucleus but is sequestered from its normal growth-promoting target genes--a phenomenon we term "nuclear seclusion." Hence, we posit that in addition to its well-known role in stimulating cellular metabolism in response to nutrients, TOR also promotes wing growth by liberating Yki from nuclear seclusion, a parallel pathway that we propose contributes to the scaling of wing size with nutrient availability.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics and Development, Columbia University, New York, New York, United States of America; Division of Biology, Imperial College London, London, United Kingdom.

ABSTRACT
Organ growth is controlled by patterning signals that operate locally (e.g., Wingless/Ints [Wnts], Bone Morphogenetic Proteins [BMPs], and Hedgehogs [Hhs]) and scaled by nutrient-dependent signals that act systemically (e.g., Insulin-like peptides [ILPs] transduced by the Target of Rapamycin [TOR] pathway). How cells integrate these distinct inputs to generate organs of the appropriate size and shape is largely unknown. The transcriptional coactivator Yorkie (Yki, a YES-Associated Protein, or YAP) acts downstream of patterning morphogens and other tissue-intrinsic signals to promote organ growth. Yki activity is regulated primarily by the Warts/Hippo (Wts/Hpo) tumour suppressor pathway, which impedes nuclear access of Yki by a cytoplasmic tethering mechanism. Here, we show that the TOR pathway regulates Yki by a separate and novel mechanism in the Drosophila wing. Instead of controlling Yki nuclear access, TOR signaling governs Yki action after it reaches the nucleus by allowing it to gain access to its target genes. When TOR activity is inhibited, Yki accumulates in the nucleus but is sequestered from its normal growth-promoting target genes--a phenomenon we term "nuclear seclusion." Hence, we posit that in addition to its well-known role in stimulating cellular metabolism in response to nutrients, TOR also promotes wing growth by liberating Yki from nuclear seclusion, a parallel pathway that we propose contributes to the scaling of wing size with nutrient availability.

No MeSH data available.


Related in: MedlinePlus