Heat Oscillations Driven by the Embryonic Cell Cycle Reveal the Energetic Costs of Signaling
All living systems function out of equilibrium and exchange energy in the form of heat with their environment. Thus, heat dissipation can inform on the energetic costs of cellular processes, which are largely unknown. Here, we used an isothermal calorimeter to measure heat exchanged between developing zebrafish embryos and the surrounding medium. Heat dissipation increased over time with cell number. Unexpectedly, a prominent oscillatory component of the heat dissipation, with periods matchingthe synchronous early reductive cleavage divisions, persisted even when DNA synthesis and mitosis were blocked by inhibitors. Instead, the heat dissipation oscillations were driven by the phosphorylation and dephosphorylation reactions catalyzed by the cell-cycle oscillator, the biochemical network controlling mitotic entry and exit. We propose that the high energetic cost of cell-cycle signaling reflects the significant thermodynamic burden of imposing accurate and robust timing on cell proliferation during development.
Contribution of increasing plasma membrane to the energetic cost of early zebrafish embryogenesis
How do early embryos allocate the resources stored in the sperm and egg? Recently, we established isothermal calorimetry to measure heat dissipation by living zebra fish embryos and to estimate the energetics of specific developmental events. During the reductive cleavage divisions, the rate of heat dissipation increases from the two-cell stage to the 1024-cell stage. Here we ask which cellular process(es) drive this increasing energetic cost. We present evidence that the cost is due to the increase in the total surface area of all the cells of the embryo. Thus, the increase in total plasma membrane associated with cell proliferation is likely to contribute appreciably to the total energy budget of the embryo.
Production of systemically circulating Hedgehog by the intestine couples nutrition to growth and development
In Drosophila larvae, growth and developmental timing are regulated by nutrition in a tightly coordinated fashion. Here, we show that the intestine responds tonutrient availability by regulating production of a circulating lipoprotein-associated form of the signaling protein Hedgehog (Hh). Levels of circulating Hh tune the rates of growth and developmental timing in a coordinated fashion. Circulating Hh signals to the fat body to control larval growth. It regulates developmental timing by controlling ecdysteroid production in the prothoracic gland. Circulating Hh is especially important during starvation, when it is also required for mobilization of fat body triacylglycerol (TAG) stores. Thus, we demonstratethat Hh, previously known only for its local morphogenetic functions, also acts as a lipoprotein-associatedendocrine hormone, coordinating the response of multiple tissues to nutrient availability.
Kathrin Schmeisser#, Damla Kaptan, Bharath Kumar Raghuraman, Andrej Shevchenko, Jonathan Rodenfels, Sider Penkov, Teymuras V. Kurzchalia# Mobilization of cholesterol induces the transition from quiescence to growth in Caenorhabditis elegans through steroid hormone and mTOR signaling. Commun Biol, 7(1) Art. No. 121 (2024)
Open Access DOI
Recovery from the quiescent developmental stage called dauer is an essential process in C. elegans and provides an excellent model to understand how metabolic transitions contribute to developmental plasticity. Here we show that cholesterol bound to the small secreted proteins SCL-12 or SCL-13 is sequestered in the gut lumen during the dauer state. Upon recovery from dauer, bound cholesterol undergoes endocytosis into lysosomes of intestinal cells, where SCL-12 and SCL-13 are degraded and cholesterol is released. Free cholesterol activates mTORC1 and is used for the production of dafachronic acids. This leads to promotion of protein synthesis and growth, and a metabolic switch at the transcriptional level. Thus, mobilization of sequestered cholesterol stores is the key event for transition from quiescence to growth, and cholesterol is the major signaling molecule in this process.
Suhrid Ghosh✳︎, Anna Körte✳︎, Giulia Serafini✳︎, Vinca Yadav✳︎, Jonathan Rodenfels Developmental energetics: Energy expenditure, budgets and metabolism during animal embryogenesis. Semin Cell Dev Biol, 138 83-93 (2023)
Open Access DOI
Developing embryos are metabolically active, open systems that constantly exchange matter and energy with their environment. They function out of thermodynamic equilibrium and continuously use metabolic pathways to obtain energy from maternal nutrients, in order to fulfill the energetic requirements of growth and development. While an increasing number of studies highlight the role of metabolism in different developmental contexts, the physicochemical basis of embryogenesis, or how cellular processes use energy and matter to act together and transform a zygote into an adult organism, remains unknown. As we obtain a better understanding of metabolism, and benefit from current technology development, it is a promising time to revisit the energetic cost of development and how energetic principles may govern embryogenesis. Here, we review recent advances in methodology to measure and infer energetic parameters in developing embryos. We highlight a potential common pattern in embryonic energy expenditure and metabolic strategy across animal embryogenesis, and discuss challenges and open questions in developmental energetics.
Keiichi Katsumoto#, Siham Yennek, Chunguang Chen, Luis Fernando Delgadillo Silva, Sofia Traikov, Dror Sever, Ajuna Azad, Jingdong Shan, Seppo Vainio, Nikolay Ninov, Stephan Speier, Anne Grapin-Botton# Wnt4 is heterogeneously activated in maturing β-cells to control calcium signaling, metabolism and function. Nat Commun, 13(1) Art. No. 6255 (2022)
Open Access DOI
Diabetes is a multifactorial disorder characterized by loss or dysfunction of pancreatic β-cells. β-cells are heterogeneous, exhibiting different glucose sensing, insulin secretion and gene expression. They communicate with other endocrine cell types via paracrine signals and between β-cells via gap junctions. Here, we identify the importance of signaling between β-cells via the extracellular signal WNT4. We show heterogeneity in Wnt4 expression, most strikingly in the postnatal maturation period, Wnt4-positive cells, being more mature while Wnt4-negative cells are more proliferative. Knock-out in adult β-cells shows that WNT4 controls the activation of calcium signaling in response to a glucose challenge, as well as metabolic pathways converging to lower ATP/ADP ratios, thereby reducing insulin secretion. These results reveal that paracrine signaling between β-cells is important in addition to gap junctions in controling insulin secretion. Together with previous reports of WNT4 up-regulation in obesity our observations suggest an adaptive insulin response coordinating β-cells.
Shovamayee Maharana✳︎#, Stefanie Kretschmer✳︎#, Susan Hunger, Xiao Yan, David Kuster, Sofia Traikov, Thomas Zillinger, Marc Gentzel, Shobha Elangovan, Padmanava Dasgupta, Nagaraja Chappidi, Nadja Lucas, Katharina Isabell Maser, Henrike Maatz, Alexander Rapp, Virginie Marchand, Young-Tae Chang, Yuri Motorin, Norbert Hubner, Gunther Hartmann, Anthony Hyman, Simon Alberti, Min Ae Lee-Kirsch# SAMHD1 controls innate immunity by regulating condensation of immunogenic self RNA. Mol Cell, 82(19) 3712-3728 (2022)
Recognition of pathogen-derived foreign nucleic acids is central to innate immune defense. This requires discrimination between structurally highly similar self and nonself nucleic acids to avoid aberrant inflammatory responses as in the autoinflammatory disorder Aicardi-Goutières syndrome (AGS). How vast amounts of self RNA are shielded from immune recognition to prevent autoinflammation is not fully understood. Here, we show that human SAM-domain- and HD-domain-containing protein 1 (SAMHD1), one of the AGS-causing genes, functions as a single-stranded RNA (ssRNA) 3'exonuclease, the lack of which causes cellular RNA accumulation. Increased ssRNA in cells leads to dissolution of RNA-protein condensates, which sequester immunogenic double-stranded RNA (dsRNA). Release of sequestered dsRNA from condensates triggers activation of antiviral type I interferon via retinoic-acid-inducible gene I-like receptors. Our results establish SAMHD1 as a key regulator of cellular RNA homeostasis and demonstrate that buffering of immunogenic self RNA by condensates regulates innate immune responses.
Anneline Pinson, Lei Xing, Takashi Namba, Nereo Kalebic, Jula Peters, Christina Eugster Oegema, Sofia Traikov, Katrin Reppe, Stephan Riesenberg, Tomislav Maricic, Razvan Derihaci, Pauline Wimberger, Svante Pääbo, Wieland Huttner Human TKTL1 implies greater neurogenesis in frontal neocortex of modern humans than Neanderthals. Science, 377(6611) Art. No. eabl6422 (2022)
Neanderthal brains were similar in size to those of modern humans. We sought to investigate potential differences in neurogenesis during neocortex development. Modern human transketolase-like 1 (TKTL1) differs from Neanderthal TKTL1 by a lysine-to-arginine amino acid substitution. Using overexpression in developing mouse and ferret neocortex, knockout in fetal human neocortical tissue, and genome-edited cerebral organoids, we found that the modern human variant, hTKTL1, but not the Neanderthal variant, increases the abundance of basal radial glia (bRG) but not that of intermediate progenitors (bIPs). bRG generate more neocortical neurons than bIPs. The hTKTL1 effect requires the pentose phosphate pathway and fatty acid synthesis. Inhibition of these metabolic pathways reduces bRG abundance in fetal human neocortical tissue. Our data suggest that neocortical neurogenesis in modern humans differs from that in Neanderthals.
Romy Kronstein-Wiedemann, Marlena Stadtmüller, Sofia Traikov, Mandy Georgi, Madeleine Teichert, Hesham Yosef, Jan Wallenborn, Andreas Karl, Karin Schütze, Michael Wagner, A El-Armouche, Torsten Tonn SARS-CoV-2 Infects Red Blood Cell Progenitors and Dysregulates Hemoglobin and Iron Metabolism. Stem Cell Rev Rep, 18(5) 1809-1821 (2022)
Open Access DOI
SARS-CoV-2 infection causes acute respiratory distress, which may progress to multiorgan failure and death. Severe COVID-19 disease is accompanied by reduced erythrocyte turnover, low hemoglobin levels along with increased total bilirubin and ferritin serum concentrations. Moreover, expansion of erythroid progenitors in peripheral blood together with hypoxia, anemia, and coagulopathies highly correlates with severity and mortality. We demonstrate that SARS-CoV-2 directly infects erythroid precursor cells, impairs hemoglobin homeostasis and aggravates COVID-19 disease.
Xingbo Yang✳︎#, Matthias Heinemann, Jonathon Howard, Greg Huber, Srividya Iyer-Biswas, Guillaume Le Treut, Michael Lynch, Kristi L Montooth, Daniel Needleman, Simone Pigolotti, Jonathan Rodenfels, Pierre Ronceray, Sadasivan Shankar, Iman Tavassoly, Shashi Thutupalli, Denis V Titov, Jin Wang, Peter J Foster✳︎# Physical bioenergetics: Energy fluxes, budgets, and constraints in cells. Proc Natl Acad Sci U.S.A., 118(26) Art. No. e2026786118 (2021)
Cells are the basic units of all living matter which harness the flow of energy to drive the processes of life. While the biochemical networks involved in energy transduction are well-characterized, the energetic costs and constraints for specific cellular processes remain largely unknown. In particular, what are the energy budgets of cells? What are the constraints and limits energy flows impose on cellular processes? Do cells operate near these limits, and if so how do energetic constraints impact cellular functions? Physics has provided many tools to study nonequilibrium systems and to define physical limits, but applying these tools to cell biology remains a challenge. Physical bioenergetics, which resides at the interface of nonequilibrium physics, energy metabolism, and cell biology, seeks to understand how much energy cells are using, how they partition this energy between different cellular processes, and the associated energetic constraints. Here we review recent advances and discuss open questions and challenges in physical bioenergetics.
Jonathan Rodenfels, Karla M. Neugebauer Calorimetric Heat Dissipation Measurements of Developing Zebrafish Embryos. Methods Mol Biol, 2329 311-321 (2021)
Living cells, tissues and organisms are open, metabolically active systems that constantly exchange matter and energy with their environment in the form of heat. The heat exchanged is equal to the net enthalpy of all chemical reactions taking place within the system. Thus, heat dissipation can inform on the energetic costs of the constellation of cellular processes that contribute to physiology and address unanswered questions about development, responses to the environment, signaling and metabolic pathways, and the roles of morphological substructures. Here, we describe the methods we established to measure the heat dissipated by early zebrafish embryos undergoing synchronous cell cycles of cleavage stage embryogenesis, using isothermal calorimetry. The non-invasive nature of calorimetry and the versatility of these methods enables the investigation of the energetic costs of embryonic development and of the cellular processes associated with the early embryonic cell cycles.
Wilhelm Palm, Jonathan Rodenfels Understanding the role of lipids and lipoproteins in development. Development, 147(24) Art. No. dev186411 (2020)
Lipids exert diverse functions in living organisms. They form cellular membranes, store and transport energy and play signalling roles. Some lipid species function in all of these processes, making them ideal candidates to coordinate metabolism with cellular homeostasis and animal development. This theme was central to Suzanne Eaton's research in the fruit fly, Drosophila Here, we discuss her work on membrane lipid homeostasis in changing environments and on functions for lipids in the Hedgehog signalling pathway. We further highlight lipoproteins as inter-organ carriers of lipids and lipid-linked morphogens, which communicate dietary and developmental signals throughout the organism.
Jonathan Rodenfels, Pablo Sartori, Stefan Golfier, Kartikeya Nagendra, Karla M. Neugebauer, Jonathon Howard Contribution of increasing plasma membrane to the energetic cost of early zebrafish embryogenesis. Mol Biol Cell, 31(7) 520-526 (2020)
How do early embryos allocate the resources stored in the sperm and egg? Recently, we established isothermal calorimetry to measure heat dissipation by living zebra-fish embryos and to estimate the energetics of specific developmental events. During the reductive cleavage divisions, the rate of heat dissipation increases from ∼60 nJ · s-1 at the two-cell stage to ∼90 nJ · s-1 at the 1024-cell stage. Here we ask which cellular process(es) drive this increasing energetic cost. We present evidence that the cost is due to the increase in the total surface area of all the cells of the embryo. First, embryo volume stays constant during the cleavage stage, indicating that the increase is not due to growth. Second, the heat increase is blocked by nocodazole, which inhibits DNA replication, mitosis, and cell division; this suggests some aspect of cell proliferation contributes to these costs. Third, the heat increases in proportion to the total cell surface area rather than total cell number. Fourth, the heat increase falls within the range of the estimated costs of maintaining and assembling plasma membranes and associated proteins. Thus, the increase in total plasma membrane associated with cell proliferation is likely to contribute appreciably to the total energy budget of the embryo.
Jonathan Rodenfels, Karla M. Neugebauer, Jonathon Howard Heat Oscillations Driven by the Embryonic Cell Cycle Reveal the Energetic Costs of Signaling. Dev Cell, 48(5) 646-658 (2019)
All living systems function out of equilibrium and exchange energy in the form of heat with their environment. Thus, heat flow can inform on the energetic costs of cellular processes, which are largely unknown. Here, we have repurposed an isothermal calorimeter to measure heat flow between developing zebrafish embryos and the surrounding medium. Heat flow increased over time with cell number. Unexpectedly, a prominent oscillatory component of the heat flow, with periods matching the synchronous early reductive cleavage divisions, persisted even when DNA synthesis and mitosis were blocked by inhibitors. Instead, the heat flow oscillations were driven by the phosphorylation and dephosphorylation reactions catalyzed by the cell-cycle oscillator, the biochemical network controlling mitotic entry and exit. We propose that the high energetic cost of cell-cycle signaling reflects the significant thermodynamic burden of imposing accurate and robust timing on cell proliferation during development.
Patricia Heyn, Hanna Salmonowicz, Jonathan Rodenfels, Karla M. Neugebauer Activation of transcription enforces the formation of distinct nuclear bodies in zebrafish embryos. RNA Biol, 14(6) 752-760 (2017)
Nuclear bodies are cellular compartments that lack lipid bilayers and harbor specific RNAs and proteins. Recent proposals that nuclear bodies form through liquid-liquid phase separation leave the question of how different nuclear bodies maintain their distinct identities unanswered. Here we investigate Cajal bodies (CBs), histone locus bodies (HLBs) and nucleoli - involved in assembly of the splicing machinery, histone mRNA 3' end processing, and rRNA processing, respectively - in the embryos of the zebrafish, Danio rerio. We take advantage of the transcriptional silence of the 1-cell embryo and follow nuclear body appearance as zygotic transcription becomes activated. CBs are present from fertilization onwards, while HLB and nucleolar components formed foci several hours later when histone genes and rDNA became active. HLB formation was blocked by transcription inhibition, suggesting nascent histone transcripts recruit HLB components like U7 snRNP. Surprisingly, we found that U7 base-pairing with nascent histone transcripts was not required for localization to HLBs. Rather, the type of Sm ring assembled on U7 determined its targeting to HLBs or CBs; the spliceosomal Sm ring targeted snRNAs to CBs while the specialized U7 Sm-ring localized to HLBs, demonstrating the contribution of protein constituents to the distinction among nuclear bodies. Thus, nucleolar, HLB, and CB components can mix in early embryogenesis when transcription is naturally or artificially silenced. These data support a model in which transcription of specific gene loci nucleates nuclear body components with high specificity and fidelity to perform distinct regulatory functions.
Oksana Lavrynenko, Jonathan Rodenfels, Maria Carvalho, Natalie Dye, Rene Lafont, Suzanne Eaton, Andrej Shevchenko The ecdysteroidome of Drosophila: influence of diet and development. Development, 142(21) 3758-3768 (2015)
Ecdysteroids are the hormones regulating development, physiology and fertility in arthropods, which synthesize them exclusively from dietary sterols. But how dietary sterol diversity influences the ecdysteroid profile, how animals ensure the production of desired hormones and whether there are functional differences between different ecdysteroids produced in vivo remains unknown. This is because currently there is no analytical technology for unbiased, comprehensive and quantitative assessment of the full complement of endogenous ecdysteroids. We developed a new LC-MS/MS method to screen the entire chemical space of ecdysteroid-related structures and to quantify known and newly discovered hormones and their catabolites. We quantified the ecdysteroidome in Drosophila melanogaster and investigated how the ecdysteroid profile varies with diet and development. We show that Drosophila can produce four different classes of ecdysteroids, which are obligatorily derived from four types of dietary sterol precursors. Drosophila makes makisterone A from plant sterols and epi-makisterone A from ergosterol, the major yeast sterol. However, they prefer to selectively utilize scarce ergosterol precursors to make a novel hormone 24,28-dehydromakisterone A and trace cholesterol to synthesize 20-hydroxyecdysone. Interestingly, epi-makisterone A supports only larval development, whereas all other ecdysteroids allow full adult development. We suggest that evolutionary pressure against producing epi-C-24 ecdysteroids might explain selective utilization of ergosterol precursors and the puzzling preference for cholesterol.
Jonathan Rodenfels, Oksana Lavrynenko, Sophie Ayciriex, Julio Sampaio, Maria Carvalho, Andrej Shevchenko, Suzanne Eaton Production of systemically circulating Hedgehog by the intestine couples nutrition to growth and development. Genes Dev, 28(23) 2636-2651 (2014)
In Drosophila larvae, growth and developmental timing are regulated by nutrition in a tightly coordinated fashion. The networks that couple these processes are far from understood. Here, we show that the intestine responds to nutrient availability by regulating production of a circulating lipoprotein-associated form of the signaling protein Hedgehog (Hh). Levels of circulating Hh tune the rates of growth and developmental timing in a coordinated fashion. Circulating Hh signals to the fat body to control larval growth. It regulates developmental timing by controlling ecdysteroid production in the prothoracic gland. Circulating Hh is especially important during starvation, when it is also required for mobilization of fat body triacylglycerol (TAG) stores. Thus, we demonstrate that Hh, previously known only for its local morphogenetic functions, also acts as a lipoprotein-associated endocrine hormone, coordinating the response of multiple tissues to nutrient availability.
Christof Osman, Mathias Haag, Christoph Potting, Jonathan Rodenfels, Phat Vinh Dip, Felix T. Wieland, Britta Brügger, Benedikt Westermann, Thomas Langer The genetic interactome of prohibitins: coordinated control of cardiolipin and phosphatidylethanolamine by conserved regulators in mitochondria. J Cell Biol, 184(4) 583-596 (2009)
Prohibitin ring complexes in the mitochondrial inner membrane regulate cell proliferation as well as the dynamics and function of mitochondria. Although prohibitins are essential in higher eukaryotes, prohibitin-deficient yeast cells are viable and exhibit a reduced replicative life span. Here, we define the genetic interactome of prohibitins in yeast using synthetic genetic arrays, and identify 35 genetic interactors of prohibitins (GEP genes) required for cell survival in the absence of prohibitins. Proteins encoded by these genes include members of a conserved protein family, Ups1 and Gep1, which affect the processing of the dynamin-like GTPase Mgm1 and thereby modulate cristae morphogenesis. We show that Ups1 and Gep1 regulate the levels of cardiolipin and phosphatidylethanolamine in mitochondria in a lipid-specific but coordinated manner. Lipid profiling by mass spectrometry of GEP-deficient mitochondria reveals a critical role of cardiolipin and phosphatidylethanolamine for survival of prohibitin-deficient cells. We propose that prohibitins control inner membrane organization and integrity by acting as protein and lipid scaffolds.