Belgium

History dependent muscle properties have been described since the early 1950s1 . History dependent properties refer to residual force depression and residual force enhancement, rFE, observed when an active muscle is shortened or stretched, respectively. Here, I will focus exclusively on rFE.
rFE is typically measured as the increase in isometric force following active stretching of a muscle, compared to the corresponding isometric force not preceded by active stretching. Despite 75 years of research, the mechanisms underlying rFE remain unknown, although some initially proposed mechanisms have been unequivocally rejected. To identify the molecular events responsible for rFE, we have performed experiments ranging from single actin-myosin interactions using laser traps2 , to in-vivo human skeletal muscles activated voluntarily or by electrical nerve stimulation3 .
Summarizing the results of these studies, it appears (i) that rFE is associated with an increase in force of passive structural proteins, (ii) that this increase in passive force is associated with titin, and (iii) that the increase in titin force is associated with an increase in titin stiffness. We speculate that titin stiffness is increased by binding of proximal titin segments to actin, thereby reducing titin’s free spring length, causing an increase in titin force when a muscle is actively stretched. We further speculate that titin-actin binding is regulated by the exposure of attachment sites on actin through the inward movement of tropomyosin upon strong cross-bridge binding.
1 Abbott &amp; Aubert (1952). J Physiol. 117(1),77.
2 Mehta &amp; Herzog (2008). J Biomech, 41(7),1611-1615.
3 Lee &amp; Herzog (2002). J Physiol, 545(1),321-330.

SEB Conference 2025

Characterization of Muscle Properties Across Scales: from Single Cross-Bridges to In Vivo Human Skeletal Muscles

three filament model

cross-bridge function

muscle properties

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SEB Conference 2024

SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

History dependent muscle properties have been described since the early 1950s1 . History dependent properties refer to residual force depression and residual force enhancement, rFE, observed when an active muscle is shortened or stretched, respectively. Here, I will focus exclusively on rFE.
rFE is typically measured as the increase in isometric force following active stretching of a muscle, compared to the corresponding isometric force not preceded by active stretching. Despite 75 years of research, the mechanisms underlying rFE remain unknown, although some initially proposed mechanisms have been unequivocally rejected. To identify the molecular events responsible for rFE, we have performed experiments ranging from single actin-myosin interactions using laser traps2 , to in-vivo human skeletal muscles activated voluntarily or by electrical nerve stimulation3 .
Summarizing the results of these studies, it appears (i) that rFE is associated with an increase in force of passive structural proteins, (ii) that this increase in passive force is associated with titin, and (iii) that the increase in titin force is associated with an increase in titin stiffness. We speculate that titin stiffness is increased by binding of proximal titin segments to actin, thereby reducing titin’s free spring length, causing an increase in titin force when a muscle is actively stretched. We further speculate that titin-actin binding is regulated by the exposure of attachment sites on actin through the inward movement of tropomyosin upon strong cross-bridge binding.
1 Abbott & Aubert (1952). J Physiol. 117(1),77.
2 Mehta & Herzog (2008). J Biomech, 41(7),1611-1615.
3 Lee & Herzog (2002). J Physiol, 545(1),321-330.

technical paper

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Warming affects a range of individual traits in aquatic ectotherms, with cascading effects on species interactions and community structure and dynamics. In addition to the direct kinetic effects of temperature, warming often leads to a smaller body size, which indirectly affects individual life history, population dynamics and species interactions. We provide a framework to study the effects of warming-induced changes in body size at multiple levels of biological organisation and use a tri-trophic food chain model with size-and temperature-dependent vital rates and species interaction strengths to explore the role of direct kinetic effects of temperature and warming-induced smaller body sizes on community structure along resource productivity and temperature gradients. We find that community structure, including the propensity for sudden collapse along environmental gradients, is primarily driven by the direct kinetic effects of temperature on vital rates and thermal mismatches between the consumer and predator species, overshadowing the effects mediated by shrinking body sizes. Overall, our study shows that warming-induced reductions in body size modulate population- and community-level responses to warming and emphasises the need for robust data on the temperature dependence of basic processes, such as body growth, to make more accurate predictions about the future impact of global change on communities and ecosystems.

Indirect effects of warming-induced body size reductions versus direct kinetic effects of warming: implications for population and community responses to changing climate

Aquatic ecosystems are increasingly disrupted by anthropogenic stressors such as nutrient-driven eutrophication and global warming. Understanding these multi-stressor effects is crucial yet challenging due to the complexity of ecosystem interactions. Here, we investigated the impacts of nitrate enrichment (5, 50, or 200 mg/L) and heatwaves on semi-realistic mesocosm aquatic ecosystems, assessing primary producers (algae, submerged and floating macrophytes) and consumers (Daphnia, fish). The findings revealed that heatwaves and nutrient loading influence ecosystems in complex ways. At the ecosystem level, we did not observe a synergistic positive effect of heatwaves and nitrate on algal growth, as is often reported in studies focusing on single organisms. Moreover, results revealed that nitrate enrichment alone reduced submerged macrophyte growth while promoting floating macrophyte dominance. Combined nitrate and heatwave stressors led to a decline in both macrophyte types, though the reduction was not statistically significant for floating macrophytes. We can conclude that neither stressor alone shifted the ecosystem to a phytoplankton-dominated turbid state; however, nitrate enrichment alone resulted in a floating macrophyte-dominated turbid state. Additionally, nitrate and heatwave interactions negatively affected both primary (Daphnia) and secondary (fish) consumers, potentially allowing the ecosystem to shift to a phytoplankton-dominated turbid under extreme conditions. In conclusion, these findings underscore the species-specific and time-dependent nature of stressors impacts. Moreover, our finding emphasizes the importance of conducting additional mesocosm experiments with longer durations and more diverse species compositions to elucidate ecosystem-level responses and adaptive capacities under multi-stressor scenarios.

GETTING A BURN-OUT: HOW HEATWAVES IMPACT EUTROPHIC FRESHWATER ECOSYSTEMS

Palaeontologists have long been fascinated with how ancient organisms moved and fed, butit has proved difficult to address these questions in ways that allow specific hypotheses to betested. As a result, endeavours in the field are sometimes dismissed as unscientific ‘just-so’stories. However, the increasing availability of techniques for visualizing and analysingfossils digitally and in three dimensions has provided a framework for testing specifichypotheses in extinct taxa. One such method is computational fluid dynamics (CFD), a toolfor simulating flows of fluids and their interaction with solid surfaces. In this talk, I will presentcase studies of how CFD has been used to test functional hypotheses in fossil taxa,informing on the ecology and evolution of ancient organisms. I will also outline somepossible future directions in palaeontological CFD analyses, such as simulations acrosslarger spatial scales and coupling different physics models. Ultimately, I aim to show howCFD has the potential to form a key part of the palaeontologist’s toolkit for bringing fossils‘back to life’.

Ancient life in moving fluids: using computational fluid dynamics to test functionaland ecological hypotheses in fossil taxa

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous environmental contaminants that bioaccumulate and cause harmful effects to organisms. Despite their widespread presence, few studies have investigated how environmental factors influence PFAS toxicity. This study assessed the combined effects of warming scenarios and PFAS mixtures on the metabolic and swimming performance of sheepshead minnows (Cyprinodon variegatus). Fish were exposed to a mixture of PFOS and PFOA (target concentration: 100 ng/mL, consistent with the US EPA’s Aquatic Life Criteria for chronic exposures) under three temperature conditions (24°C, 26°C, and 28.5°C). Metabolic variables (SMR – standard metabolic rate, MMR – maximum metabolic rate, AS – aerobic scope) and critical swimming speed (Ucrit) were measured after 28 days of exposure. Results revealed a significant interaction between temperature and PFAS on AS, with fish exposed to PFAS showing lower AS at 28.5°C compared to those in PFAS-free water. This reduction in AS was attributed to a decrease in MMR at 28.5°C (though not statistically significant), while SMR remained unchanged. Ucrit followed a similar trend to AS and MMR but was not statistically significant. As Ucrit is closely linked to aerobic metabolic performance, these findings suggest that energy-demanding compensatory mechanisms induced by the temperature-PFAS interaction may have been prioritized over swimming effort. Impairments to AS, a proxy for individual fitness, could reduce overall fish performance, potentially affecting growth and reproduction. Overall, this study suggests that PFAS-induced impairments to AS may be exacerbated under future climate scenarios, posing a significant threat to the health of ecosystems.

The heat and the hazard: Combined effects of PFAS and temperature on Sheepshead Minnow performance

Ocean warming resulting from natural or anthropogenic processes require ectothermic species, such as fishes, to be able to sustain higher energetic costs. This can be particularly challenging when additionally faced with environmental threats such as oil spills. Crude oil contains a complex mixture of polycyclic aromatic compounds (PAC), which can have negative effects on marine species such as cardiac impairment in fishes. Because the heart plays a central role in sustaining energy demand during warming, PAC-induced cardiac perturbations could have detrimental impacts on the fish’s warming tolerance. I am investigating the physiological impacts of acute (24 hr) PAC exposure (methylnaphthalene, naphthalene, phenanthrene) on cardiac thermal tolerance in larval and juvenile lumpfish (Cyclopterus lumpus), an ecologically and economically important cold-water fish. Thusfar, I found that juvenile lumpfish are resistant to relevant levels of naphthalene and phenanthrene, whereas methylnaphthalene reduced peak heart rate (fH ) and the temperature of peak fH  and cardiac arrhythmia. Understanding the combined effects of oil exposure and warming can help us better predict the severity of oil spills in our changing climate and their impact on marine fishes.

The effects of polycyclic aromatic compound exposure on cardiac thermal tolerance of larval and juvenile lumpfish (Cyclopterus lumpus)

Autophagy is the cellular clearing and recycling program that degrades cytoplasmic content in lysosomes. This process takes place in all cells and is further induced during cellular stress. Besides its crucial role as a quality control mechanism, autophagy is also involved in a host of other functions such as growth and differentiation, metabolic regulation and as an alternative energy source through a type of selective autophagy called lipophagy. Lipophagy is the most effective way to mobilize fatty acids (FAs) which prevents FA-mediated toxicity and is the preferred mechanism to generate energy during starvation. Lipophagy selectively degrades lipid droplets (LD). LDs are organelles formed by cholesterol and triacylglycerols (TG) surrounded by a phospholipid membrane serving as dynamic hubs of cellular lipid metabolism by sequestering excess of FAs. Lipophagy has mapped autophagy as an emerging player in lipid metabolism. Thus, understanding how this catabolic process happens in different scenarios can help to understand deeper lipid metabolism, we will show how to measure lipophagy in different contexts and its biological meaning.

Lipophagy: a process more relevant than just getting fuel

Hypomethylation in plants is associated with improved stress responses and is therefore a favourable trait. However, when methylation mutants are produced there is often a transgenerational decrease in fitness, meaning this is not a viable avenue to explore in crops. Previously this has been associated with ectopic methylation (ibm1) and alternative splicing of the IBM1 transcript due to changes in intron methylation (met1-3). We aimed to determine the responsibility of IBM1 in this phenotype, and investigate whether other genes are involved.
Utilising a set of epigenetics recombinant inbred lines (epiRILs), where met1-3 was crossed with Col-0 to produce a ‘mosaic pattern’ in DNA methylation, a ditch in chromosome 3 where inheritance was solely Col-0 was identified in the F8 generation. Within this region, genes were mined from the F1, selected based on hemimethlyation. One other gene, VHA, was identified to have a similar methylation profile to IBM1 and has a complementary expression within the flower. We hypothesized that the interaction of IBM1 and VHA could explain the transgenerational decrease in fitness observed inmet1-3plants. We generated RNA-seq and methylomic data in the pollen and carpels to assess the impacts of this interaction, and a range of genetic approaches were applied including crossing of IBM1 and VHA knockout mutants and CRISPR-Cas9 to generate double mutants.
We propose there is incompatibility between the pollen and carpels of these methylation mutants, ultimately resulting in decreased fitness and viability.

Why do hypomethylated plants display transgenerational infertility?

Global warming intensifies flooding, causing US$7.8 billion in annual agricultural damages, making it the second most destructive disaster after drought. Plant flood tolerance depends on structural and physiological traits like adventitious roots and hypocotyl hypertrophy, but tomato plants are particularly sensitive to flooding. Current tomato varieties lack sufficient flooding tolerance, leading to significant crop losses. Introgression lines (ILs) provide genetic diversity, precise trait mapping, and improved flood resilience, enabling stable production under changing conditions. We hypothesized that tomato ILs IL8-1 and IL11-4, with distinct drought responses, exhibit significantly different physiological and morphological reactions to flooding compared to the mother plant M82, likely due to differential abscisic acid-mediated stress regulation. Under oxygen deficiency (via nitrogen gas) and flooding for seven and fourteen days, parameters such as oxygen levels, redox potential, nutrient concentration, flood sensitivity index (FSI), transpiration rate, and adventitious root formation were measured. Flooding reduced midday transpiration rates by 9.72% to 67.37%, with M82 showing the least reduction. M82’s shoot dry weight was unaffected, while ILs decreased by 50%. M82 developed 10% stem hypertrophy and had the lowest FSI (27.35%). Despite forming more adventitious roots, ILs were more sensitive to flooding. This research highlights IL potential for breeding flood-resilient tomatoes.

Exploring ABA-Mediated Flood Tolerance Mechanisms in Tomato: Insights from Introgression Lines

Biochar, a soil amendment known to influence plant growth by modifying soil properties, nutrient availability, and physiological processes, has been extensively studied in field and soilless cultivation systems. However, its molecular effects on plants remain poorly understood. Research on crops, such as tomato, pepper, soybean, lettuce, and wheat, has revealed different gene expression responses to biochar, with growth-related genes generally up-regulated, while defense-related genes show more variable trends. This study investigates the molecular effect of biochar on young blueberry (Vaccinium corymbosum L.) plants (cv. Sierra). To evaluate the effect of biochar on plant growth and gene expression, before transplanting, it was added at 0, 5, and 10% v/v in combination with a coir-based substrate, in 10L pots. Key parameters, including plant height, branch number, and chlorophyll content, were measured. Additionally, photosynthetic performance was evaluated through leaf gas exchange analysis and qRT-PCR was conducted to assess the expression of four growth-related and four defense-related genes. The results showed that biochar influenced plant growth and physiology in a concentration-dependent manner. At 10% biochar, plant height significantly decreased, while branch number remained unaffected. Photosynthetic efficiency did not seem to be influenced by the different substrates tested, even if chlorophyll content was lower in biochar-treated plants. Gene expression analysis revealed up-regulation of auxin-responsive and sugar transporter genes, while defense-related genes displayed variable expression patterns based on biochar concentration. These findings suggest biochar modulates physiological and molecular processes in blueberries, making further research necessary to optimize its application strategies and assess long-term effects.

Exploring the impact of biochar on growth and molecular responses in young blueberry (Vaccinium corymbosum L.), cv. Sierra, plants

Artificial intelligence methods are a key enabler in high throughput phenotyping. With AI, we can phenotype plants at large scale, more accurately, and often faster than humans. However, there have been fewer attempts in incorporating AI in modelling genotype by environment by management interactions. This talks offers a reflection on how AI methods can advance GxExM modelling, starting with some motivating examples from the PHENET project: How AI can improve estimating yields in multi-environment breeding trials? How hybrid models, combining neural networks with process based models, can improve phenology estimation models? And finally how machine vision advances can be combined with 3d structural models towards crop growth digital twins? We conclude with a research agenda for the years to come and some open problems in this emerging field.

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Indirect effects of warming-induced body size reductions versus direct kinetic effects of warming: implications for population and community responses to changing climate

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