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TIF-IA-dependent regulation of ribosome synthesis in drosophila muscle is required to maintain systemic insulin signaling and larval growth.

Ghosh A, Rideout EJ, Grewal SS - PLoS Genet. (2014)

Bottom Line: When we mimic this decrease in muscle ribosome synthesis using RNAi-mediated knockdown of TIF-IA, we observe delayed larval development and reduced body growth.This reduction in growth is caused by lowered systemic insulin signaling via two endocrine responses: reduced expression of Drosophila insulin-like peptides (dILPs) from the brain and increased expression of Imp-L2-a secreted factor that binds and inhibits dILP activity-from muscle.Finally, we show that activation of TOR specifically in muscle can increase overall body size and this effect requires TIF-IA function.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, and Clark H. Smith Brain Tumour Centre, Southern Alberta Cancer Research Institute, University of Calgary, Health Research Innovation Center, Calgary, Alberta, Canada.

ABSTRACT
The conserved TOR kinase signaling network links nutrient availability to cell, tissue and body growth in animals. One important growth-regulatory target of TOR signaling is ribosome biogenesis. Studies in yeast and mammalian cell culture have described how TOR controls rRNA synthesis-a limiting step in ribosome biogenesis-via the RNA Polymerase I transcription factor TIF-IA. However, the contribution of TOR-dependent ribosome synthesis to tissue and body growth in animals is less clear. Here we show in Drosophila larvae that ribosome synthesis in muscle is required non-autonomously to maintain normal body growth and development. We find that amino acid starvation and TOR inhibition lead to reduced levels of TIF-IA, and decreased rRNA synthesis in larval muscle. When we mimic this decrease in muscle ribosome synthesis using RNAi-mediated knockdown of TIF-IA, we observe delayed larval development and reduced body growth. This reduction in growth is caused by lowered systemic insulin signaling via two endocrine responses: reduced expression of Drosophila insulin-like peptides (dILPs) from the brain and increased expression of Imp-L2-a secreted factor that binds and inhibits dILP activity-from muscle. We also observed that maintaining TIF-IA levels in muscle could partially reverse the starvation-mediated suppression of systemic insulin signaling. Finally, we show that activation of TOR specifically in muscle can increase overall body size and this effect requires TIF-IA function. These data suggest that muscle ribosome synthesis functions as a nutrient-dependent checkpoint for overall body growth: in nutrient rich conditions, TOR is required to maintain levels of TIF-IA and ribosome synthesis to promote high levels of systemic insulin, but under conditions of starvation stress, reduced muscle ribosome synthesis triggers an endocrine response that limits systemic insulin signaling to restrict growth and maintain homeostasis.

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Related in: MedlinePlus

Fat-specific and lymph gland-specific TIF-IA inhibition has modest effects on growth and development.(A) Developmental timing from larval hatching to pupation of r4>+ and r4>TIF-IA IR animals, n = 158, n - number of larvae assessed per genotype, (mean time to pupation: r4>+, 6.4 days vs. r4>TIF-IA IR, 6.7 days, *P<0.05, Mann-Whitney U test). (B) Representative images of r4>+ (top) and r4>TIF-IA IR (bottom) larvae. Numbers at the bottom of the panel indicates hours AEL. (C) Pupal volume of r4>+ (n = 100) and r4>TIF-IA IR pupae (n = 28), n - number of pupae per genotype, (P = 0.92, Student's t-test). (D) Developmental timing from larval hatching to pupation of ppl>+ and ppl>TIF-IA IR animals, n = 120, n - number of larvae assessed per genotype, (mean time to pupation: ppl>+ 6.1 days vs. ppl>TIF-IA IR 6.1 days, not significant, Mann-Whitney U test). (E) Pupal volume of ppl>+ (n = 41) and ppl>TIF-IA IR pupae (n = 44), (P = 0.92, Student's t-test). (F) Developmental timing from larval hatching to pupation of hml>+ and hml>TIF-IA IR animals, n = 192, n - number of larvae assessed per genotype, (mean time to pupation: hml>+, 7.2 days vs. hml>TIF-IA IR, 6.9 days, *P<0.05, Mann-Whitney U test). (G) Developmental timing from larval hatching to pupation of pxn>+ and pxn>TIF-IA IR animals, n = 103, n - number of pupae counted per genotype, (mean time to pupation: pxn>+, 7.8 days vs. pxn>TIF-IA IR, 7.8 days, not significant, Mann-Whitney U test). All error bars indicate SEM.
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pgen-1004750-g003: Fat-specific and lymph gland-specific TIF-IA inhibition has modest effects on growth and development.(A) Developmental timing from larval hatching to pupation of r4>+ and r4>TIF-IA IR animals, n = 158, n - number of larvae assessed per genotype, (mean time to pupation: r4>+, 6.4 days vs. r4>TIF-IA IR, 6.7 days, *P<0.05, Mann-Whitney U test). (B) Representative images of r4>+ (top) and r4>TIF-IA IR (bottom) larvae. Numbers at the bottom of the panel indicates hours AEL. (C) Pupal volume of r4>+ (n = 100) and r4>TIF-IA IR pupae (n = 28), n - number of pupae per genotype, (P = 0.92, Student's t-test). (D) Developmental timing from larval hatching to pupation of ppl>+ and ppl>TIF-IA IR animals, n = 120, n - number of larvae assessed per genotype, (mean time to pupation: ppl>+ 6.1 days vs. ppl>TIF-IA IR 6.1 days, not significant, Mann-Whitney U test). (E) Pupal volume of ppl>+ (n = 41) and ppl>TIF-IA IR pupae (n = 44), (P = 0.92, Student's t-test). (F) Developmental timing from larval hatching to pupation of hml>+ and hml>TIF-IA IR animals, n = 192, n - number of larvae assessed per genotype, (mean time to pupation: hml>+, 7.2 days vs. hml>TIF-IA IR, 6.9 days, *P<0.05, Mann-Whitney U test). (G) Developmental timing from larval hatching to pupation of pxn>+ and pxn>TIF-IA IR animals, n = 103, n - number of pupae counted per genotype, (mean time to pupation: pxn>+, 7.8 days vs. pxn>TIF-IA IR, 7.8 days, not significant, Mann-Whitney U test). All error bars indicate SEM.

Mentions: We also examined the organismal effects of TIF-IA knockdown in other tissues. We used two fat body GAL4 drivers (r4-GAL4 and ppl-GAL4) to express UAS-TIF-IA IR during larval development. We found that r4>TIF-IA IR larvae showed a modest, although statistically significant delay in both developmental timing - time from larval hatching to pupation (Figure 3A) - and growth (Figure 3B), but showed no significant change in body size compared to control (r4>+) animals (Figure 3C). Co-overexpression of UAS-Tsc1 and UAS-Tsc2 - negative regulators of TORC1 – using r4-GAL4 led to marked reduction in body growth, thus confirming the effectiveness of the driver (Figure S4). We also found that ppl>TIF-IA IR larvae showed no significant difference in developmental timing (Figure 3D) or final body size (Figure 3E) compared to controls (ppl>+). We also examined the effects of TIF-IA knockdown in the larval lymph gland and hemocytes using two different drivers, hemolectin (hml)-GAL4 and peroxidasin (pxn)-GAL4. In both cases, we observed no statistically significant decrease in larval development (Figure 3F, G). In fact, larval development was modestly, although significantly, accelerated in hml>TIF-IA IR larvae.


TIF-IA-dependent regulation of ribosome synthesis in drosophila muscle is required to maintain systemic insulin signaling and larval growth.

Ghosh A, Rideout EJ, Grewal SS - PLoS Genet. (2014)

Fat-specific and lymph gland-specific TIF-IA inhibition has modest effects on growth and development.(A) Developmental timing from larval hatching to pupation of r4>+ and r4>TIF-IA IR animals, n = 158, n - number of larvae assessed per genotype, (mean time to pupation: r4>+, 6.4 days vs. r4>TIF-IA IR, 6.7 days, *P<0.05, Mann-Whitney U test). (B) Representative images of r4>+ (top) and r4>TIF-IA IR (bottom) larvae. Numbers at the bottom of the panel indicates hours AEL. (C) Pupal volume of r4>+ (n = 100) and r4>TIF-IA IR pupae (n = 28), n - number of pupae per genotype, (P = 0.92, Student's t-test). (D) Developmental timing from larval hatching to pupation of ppl>+ and ppl>TIF-IA IR animals, n = 120, n - number of larvae assessed per genotype, (mean time to pupation: ppl>+ 6.1 days vs. ppl>TIF-IA IR 6.1 days, not significant, Mann-Whitney U test). (E) Pupal volume of ppl>+ (n = 41) and ppl>TIF-IA IR pupae (n = 44), (P = 0.92, Student's t-test). (F) Developmental timing from larval hatching to pupation of hml>+ and hml>TIF-IA IR animals, n = 192, n - number of larvae assessed per genotype, (mean time to pupation: hml>+, 7.2 days vs. hml>TIF-IA IR, 6.9 days, *P<0.05, Mann-Whitney U test). (G) Developmental timing from larval hatching to pupation of pxn>+ and pxn>TIF-IA IR animals, n = 103, n - number of pupae counted per genotype, (mean time to pupation: pxn>+, 7.8 days vs. pxn>TIF-IA IR, 7.8 days, not significant, Mann-Whitney U test). All error bars indicate SEM.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4214618&req=5

pgen-1004750-g003: Fat-specific and lymph gland-specific TIF-IA inhibition has modest effects on growth and development.(A) Developmental timing from larval hatching to pupation of r4>+ and r4>TIF-IA IR animals, n = 158, n - number of larvae assessed per genotype, (mean time to pupation: r4>+, 6.4 days vs. r4>TIF-IA IR, 6.7 days, *P<0.05, Mann-Whitney U test). (B) Representative images of r4>+ (top) and r4>TIF-IA IR (bottom) larvae. Numbers at the bottom of the panel indicates hours AEL. (C) Pupal volume of r4>+ (n = 100) and r4>TIF-IA IR pupae (n = 28), n - number of pupae per genotype, (P = 0.92, Student's t-test). (D) Developmental timing from larval hatching to pupation of ppl>+ and ppl>TIF-IA IR animals, n = 120, n - number of larvae assessed per genotype, (mean time to pupation: ppl>+ 6.1 days vs. ppl>TIF-IA IR 6.1 days, not significant, Mann-Whitney U test). (E) Pupal volume of ppl>+ (n = 41) and ppl>TIF-IA IR pupae (n = 44), (P = 0.92, Student's t-test). (F) Developmental timing from larval hatching to pupation of hml>+ and hml>TIF-IA IR animals, n = 192, n - number of larvae assessed per genotype, (mean time to pupation: hml>+, 7.2 days vs. hml>TIF-IA IR, 6.9 days, *P<0.05, Mann-Whitney U test). (G) Developmental timing from larval hatching to pupation of pxn>+ and pxn>TIF-IA IR animals, n = 103, n - number of pupae counted per genotype, (mean time to pupation: pxn>+, 7.8 days vs. pxn>TIF-IA IR, 7.8 days, not significant, Mann-Whitney U test). All error bars indicate SEM.
Mentions: We also examined the organismal effects of TIF-IA knockdown in other tissues. We used two fat body GAL4 drivers (r4-GAL4 and ppl-GAL4) to express UAS-TIF-IA IR during larval development. We found that r4>TIF-IA IR larvae showed a modest, although statistically significant delay in both developmental timing - time from larval hatching to pupation (Figure 3A) - and growth (Figure 3B), but showed no significant change in body size compared to control (r4>+) animals (Figure 3C). Co-overexpression of UAS-Tsc1 and UAS-Tsc2 - negative regulators of TORC1 – using r4-GAL4 led to marked reduction in body growth, thus confirming the effectiveness of the driver (Figure S4). We also found that ppl>TIF-IA IR larvae showed no significant difference in developmental timing (Figure 3D) or final body size (Figure 3E) compared to controls (ppl>+). We also examined the effects of TIF-IA knockdown in the larval lymph gland and hemocytes using two different drivers, hemolectin (hml)-GAL4 and peroxidasin (pxn)-GAL4. In both cases, we observed no statistically significant decrease in larval development (Figure 3F, G). In fact, larval development was modestly, although significantly, accelerated in hml>TIF-IA IR larvae.

Bottom Line: When we mimic this decrease in muscle ribosome synthesis using RNAi-mediated knockdown of TIF-IA, we observe delayed larval development and reduced body growth.This reduction in growth is caused by lowered systemic insulin signaling via two endocrine responses: reduced expression of Drosophila insulin-like peptides (dILPs) from the brain and increased expression of Imp-L2-a secreted factor that binds and inhibits dILP activity-from muscle.Finally, we show that activation of TOR specifically in muscle can increase overall body size and this effect requires TIF-IA function.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, and Clark H. Smith Brain Tumour Centre, Southern Alberta Cancer Research Institute, University of Calgary, Health Research Innovation Center, Calgary, Alberta, Canada.

ABSTRACT
The conserved TOR kinase signaling network links nutrient availability to cell, tissue and body growth in animals. One important growth-regulatory target of TOR signaling is ribosome biogenesis. Studies in yeast and mammalian cell culture have described how TOR controls rRNA synthesis-a limiting step in ribosome biogenesis-via the RNA Polymerase I transcription factor TIF-IA. However, the contribution of TOR-dependent ribosome synthesis to tissue and body growth in animals is less clear. Here we show in Drosophila larvae that ribosome synthesis in muscle is required non-autonomously to maintain normal body growth and development. We find that amino acid starvation and TOR inhibition lead to reduced levels of TIF-IA, and decreased rRNA synthesis in larval muscle. When we mimic this decrease in muscle ribosome synthesis using RNAi-mediated knockdown of TIF-IA, we observe delayed larval development and reduced body growth. This reduction in growth is caused by lowered systemic insulin signaling via two endocrine responses: reduced expression of Drosophila insulin-like peptides (dILPs) from the brain and increased expression of Imp-L2-a secreted factor that binds and inhibits dILP activity-from muscle. We also observed that maintaining TIF-IA levels in muscle could partially reverse the starvation-mediated suppression of systemic insulin signaling. Finally, we show that activation of TOR specifically in muscle can increase overall body size and this effect requires TIF-IA function. These data suggest that muscle ribosome synthesis functions as a nutrient-dependent checkpoint for overall body growth: in nutrient rich conditions, TOR is required to maintain levels of TIF-IA and ribosome synthesis to promote high levels of systemic insulin, but under conditions of starvation stress, reduced muscle ribosome synthesis triggers an endocrine response that limits systemic insulin signaling to restrict growth and maintain homeostasis.

Show MeSH
Related in: MedlinePlus