Periodic Reporting for period 1 - SizeGrowth (Interplay between energy and metabolism in dictating growth constrain and setting final size)
Periodo di rendicontazione: 2023-06-01 al 2025-05-31
Understanding how biological structures grow to reach and maintain their final size is a fundamental question in developmental biology, with far-reaching implications in health, disease, and aging. Despite decades of research, the mechanisms by which growth is constrained and ultimately arrested during development remain poorly understood, particularly from the perspective of energetics. Traditionally, studies on growth have focused on genetic and biochemical signaling pathways or mechanical forces; however, the energetic demands and limitations that underlie growth processes have received comparatively little attention.
This project aimed to fill that gap by investigating how energy metabolism constrains growth at the organismal and organ levels. Specifically, it focused on testing whether growth arrest during development is a consequence of internal energy limitations and how this ties into known scaling laws like Kleiber’s law, which predicts a sublinear relationship between metabolic rate and body mass. Using Drosophila melanogaster as a model, the project combined isothermal microcalorimetry, protein synthesis labeling, and high-resolution imaging to dynamically measure metabolic rates and growth in developing larvae and tissues.
The overall objectives of the project were:
To quantify how metabolic power changes during development in whole organisms and specific organs.
To test whether energy constraints drive growth arrest, through spatial limitations in transport networks (e.g. trachea), morphogen signaling gradients (e.g. Dpp), and mechanical feedback.
To determine whether metabolic rate scaling at cellular, organ, and organismal levels aligns with or deviates from established theories such as Kleiber’s law.
This research is strategically aligned with broader scientific and societal challenges, particularly in understanding the deregulation of growth in disease contexts such as cancer, cardiac hypertrophy, and developmental disorders. Growth arrest failures are hallmarks of cancer and many age-related diseases. By revealing how energetic constraints impact growth control, this project contributes crucial insight into physiological regulation mechanisms and offers new conceptual frameworks for addressing disease processes where these mechanisms go awry.
From a broader perspective, the potential impact of this project is twofold:
Scientific Impact: By integrating biophysics, developmental biology, and metabolic analysis, the project pioneers a truly interdisciplinary approach to growth regulation, offering new tools and perspectives that can be applied across model organisms and in disease models.
Societal and Clinical Relevance: Understanding how energy constrains growth opens new avenues for developing treatments that target metabolic pathways in cancer and aging. It also enriches fundamental knowledge that underlies future precision medicine strategies.
Finally, the project contributes to Europe’s scientific leadership by strengthening interdisciplinary research at the interface of biology and physics, supporting open science, and fostering career development and international mobility. Conducted at the IBDM and the Turing Centre for Living Systems (CenTuri) in Marseille, a hub for interdisciplinary research, the project exemplifies how combining experimental and theoretical sciences can lead to transformative insights into complex biological processes.
This project aimed to fill that gap by investigating how energy metabolism constrains growth at the organismal and organ levels. Specifically, it focused on testing whether growth arrest during development is a consequence of internal energy limitations and how this ties into known scaling laws like Kleiber’s law, which predicts a sublinear relationship between metabolic rate and body mass. Using Drosophila melanogaster as a model, the project combined isothermal microcalorimetry, protein synthesis labeling, and high-resolution imaging to dynamically measure metabolic rates and growth in developing larvae and tissues.
The overall objectives of the project were:
To quantify how metabolic power changes during development in whole organisms and specific organs.
To test whether energy constraints drive growth arrest, through spatial limitations in transport networks (e.g. trachea), morphogen signaling gradients (e.g. Dpp), and mechanical feedback.
To determine whether metabolic rate scaling at cellular, organ, and organismal levels aligns with or deviates from established theories such as Kleiber’s law.
This research is strategically aligned with broader scientific and societal challenges, particularly in understanding the deregulation of growth in disease contexts such as cancer, cardiac hypertrophy, and developmental disorders. Growth arrest failures are hallmarks of cancer and many age-related diseases. By revealing how energetic constraints impact growth control, this project contributes crucial insight into physiological regulation mechanisms and offers new conceptual frameworks for addressing disease processes where these mechanisms go awry.
From a broader perspective, the potential impact of this project is twofold:
Scientific Impact: By integrating biophysics, developmental biology, and metabolic analysis, the project pioneers a truly interdisciplinary approach to growth regulation, offering new tools and perspectives that can be applied across model organisms and in disease models.
Societal and Clinical Relevance: Understanding how energy constrains growth opens new avenues for developing treatments that target metabolic pathways in cancer and aging. It also enriches fundamental knowledge that underlies future precision medicine strategies.
Finally, the project contributes to Europe’s scientific leadership by strengthening interdisciplinary research at the interface of biology and physics, supporting open science, and fostering career development and international mobility. Conducted at the IBDM and the Turing Centre for Living Systems (CenTuri) in Marseille, a hub for interdisciplinary research, the project exemplifies how combining experimental and theoretical sciences can lead to transformative insights into complex biological processes.
Over the course of this Marie Curie fellowship, we carried out a series of interconnected technical and scientific activities designed to investigate how growth arrests during development, with a particular focus on the role of energy metabolism. Below is a summary of the key activities and outcomes:
1. Optimization of Size Measurements via Light Sheet Microscopy
We successfully optimized volumetric measurements of Drosophila larvae and specific organs (wing discs and salivary glands) using light sheet microscopy. By expressing GFP in whole larvae and in individual organs using the UAS-Gal4 system, we could visualize and measure organ and organism sizes within the same specimen. This enabled us to accurately track and compare growth patterns across different tissues:
Larvae exhibited clear growth arrest by the end of the larval stage.
Wing discs showed growth deceleration but not complete arrest.
Salivary glands continued growing.
These observations allowed us to refine models of proportionality and scaling within the organism.
2. Accurate Cell Number Quantification in Developing Organs
One of the challenges in developmental biology has been the accurate quantification of cell numbers in dense, late-stage tissues. With the help of Alice Gros (Lenne/Guignard labs, IBDM) who developped an image analysis pipeline to segment nuclei, we provided the first reliable cell number estimates in developing wing discs, which can contain up to 50,000 tightly packed cells at late stages. This provides a critical parameter for linking tissue growth to cellular-level metrics such as metabolic power per cell.
3. Measurement of Metabolic Power – A Multi-Technique Approach
This constitutes the core scientific innovation of the project. For the first time, we employed a combination of calorimetry, respirometry, and protein synthesis measurements to assess metabolic power across different biological scales:
Whole-organism calorimetry (in collaboration with Jonathan Rodenfels, MPI-CBG): These measurements revealed a clear sublinear scaling between metabolic power and organismal size, supporting the existence of energy constraints in developing larvae. As larvae grow, they consume proportionally less energy per unit mass, consistent with predictions from Kleiber’s law.
Explanted organ measurements: We extended our analysis to dissected wing discs and salivary glands using:
Calorimetry (ongoing),
Respirometry ( ongoing with Xingbo Yang, TU Dresden),
SCENITH protein synthesis assay (with Rafael Argüello, CIML, Marseille).
Initial findings from SCENITH suggest a linear scaling of protein synthesis with organ size, in contrast to the sublinear trend observed at the organism level. This suggests that:
- Energy constraints observed in whole larvae may not apply at the organ level, or
- Certain organs may possess mechanisms to bypass or buffer against systemic energy limitations.
Additionally, these measurements indicate that both wing discs and salivary glands rely predominantly on oxidative phosphorylation rather than glycolysis to fuel growth—providing new insight into the metabolic strategies of developing tissues.
1. Optimization of Size Measurements via Light Sheet Microscopy
We successfully optimized volumetric measurements of Drosophila larvae and specific organs (wing discs and salivary glands) using light sheet microscopy. By expressing GFP in whole larvae and in individual organs using the UAS-Gal4 system, we could visualize and measure organ and organism sizes within the same specimen. This enabled us to accurately track and compare growth patterns across different tissues:
Larvae exhibited clear growth arrest by the end of the larval stage.
Wing discs showed growth deceleration but not complete arrest.
Salivary glands continued growing.
These observations allowed us to refine models of proportionality and scaling within the organism.
2. Accurate Cell Number Quantification in Developing Organs
One of the challenges in developmental biology has been the accurate quantification of cell numbers in dense, late-stage tissues. With the help of Alice Gros (Lenne/Guignard labs, IBDM) who developped an image analysis pipeline to segment nuclei, we provided the first reliable cell number estimates in developing wing discs, which can contain up to 50,000 tightly packed cells at late stages. This provides a critical parameter for linking tissue growth to cellular-level metrics such as metabolic power per cell.
3. Measurement of Metabolic Power – A Multi-Technique Approach
This constitutes the core scientific innovation of the project. For the first time, we employed a combination of calorimetry, respirometry, and protein synthesis measurements to assess metabolic power across different biological scales:
Whole-organism calorimetry (in collaboration with Jonathan Rodenfels, MPI-CBG): These measurements revealed a clear sublinear scaling between metabolic power and organismal size, supporting the existence of energy constraints in developing larvae. As larvae grow, they consume proportionally less energy per unit mass, consistent with predictions from Kleiber’s law.
Explanted organ measurements: We extended our analysis to dissected wing discs and salivary glands using:
Calorimetry (ongoing),
Respirometry ( ongoing with Xingbo Yang, TU Dresden),
SCENITH protein synthesis assay (with Rafael Argüello, CIML, Marseille).
Initial findings from SCENITH suggest a linear scaling of protein synthesis with organ size, in contrast to the sublinear trend observed at the organism level. This suggests that:
- Energy constraints observed in whole larvae may not apply at the organ level, or
- Certain organs may possess mechanisms to bypass or buffer against systemic energy limitations.
Additionally, these measurements indicate that both wing discs and salivary glands rely predominantly on oxidative phosphorylation rather than glycolysis to fuel growth—providing new insight into the metabolic strategies of developing tissues.
This project yielded several significant technical and conceptual advances in the understanding of growth regulation during development, particularly in relation to metabolic constraints:
Quantitative Volume and Cell Number Measurements
Developed a robust workflow for accurate size measurement of whole Drosophila larvae and internal organs (wing discs and salivary glands) using light sheet microscopy.
Achieved, for the first time, reliable segmentation and quantification of cell numbers in dense developing tissues such as wing discs, through a bioinformatics collaboration.
Breakthrough in Measuring Metabolic Power at Multiple Scales
Conducted calorimetry on whole larvae, demonstrating a sublinear scaling between metabolic power and body size, in agreement with Kleiber’s law and indicating systemic energy constraints during growth.
On isolated organs, combined calorimetry, respirometry, and protein synthesis (SCENITH) techniques revealed linear scaling with organ size, suggesting either the absence of energy constraints at the organ level or mechanisms that allow organs to overcome such limitations.
Identified that oxidative phosphorylation—not glycolysis—is the primary metabolic pathway driving growth in both wing discs and salivary glands.
These results establish a new experimental and conceptual framework to understand how energy availability and usage shape tissue growth dynamics. They bridge developmental biology with bioenergetics and provide new tools to study metabolic regulation in vivo.
Quantitative Volume and Cell Number Measurements
Developed a robust workflow for accurate size measurement of whole Drosophila larvae and internal organs (wing discs and salivary glands) using light sheet microscopy.
Achieved, for the first time, reliable segmentation and quantification of cell numbers in dense developing tissues such as wing discs, through a bioinformatics collaboration.
Breakthrough in Measuring Metabolic Power at Multiple Scales
Conducted calorimetry on whole larvae, demonstrating a sublinear scaling between metabolic power and body size, in agreement with Kleiber’s law and indicating systemic energy constraints during growth.
On isolated organs, combined calorimetry, respirometry, and protein synthesis (SCENITH) techniques revealed linear scaling with organ size, suggesting either the absence of energy constraints at the organ level or mechanisms that allow organs to overcome such limitations.
Identified that oxidative phosphorylation—not glycolysis—is the primary metabolic pathway driving growth in both wing discs and salivary glands.
These results establish a new experimental and conceptual framework to understand how energy availability and usage shape tissue growth dynamics. They bridge developmental biology with bioenergetics and provide new tools to study metabolic regulation in vivo.