France

Muscles perform a number of roles, acting as motor, brakes and shock absorbers. Tendons also perform several roles, acting as transmission and/or elastic springs. But a distinct and perhaps largely overlooked role of isometric muscles and tendons is as functional tension bicycle spokes, becoming loaded in turn through simple geometry, and enabling horizontal translation during vertical weight support without high mechanical power demand. Here, quadrupedal mammal leg structure and function is considered in the context of enabling low mechanical demand at the level of the limb by maintain forces perpendicular to velocity, at the same time as providing low power supply by keeping muscles isometric when loaded, or unloaded when changing in length. These principles provide a simple account for the general structure of the scapula, serratus ventralis and triceps brachii of the forelimb, and the biceps femoris (curiously crossing across the femur), vastus, rectus femoris and tensor fasciae latae of the hindlimb. Different muscles experience tension at different stages in stance, each resulting in linkages where the links are isometric, and the limb supports predominantly vertical forces during horizontal translation.

SEB Annual Conference 2022

Legs as linkages: thinking of isometric muscles and tendons as bicycle spokes

Discover the art of creating extraordinary science at SEB’s Annual Conference at Le Corum Conference Center     in Montpellier, France from 5 to  8 July 2022.

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.

2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years.
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Please register for the conference by clicking on this link:

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2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years - Montpellier, France

technical paper

For marine species with complex life cycles, a critical question concerns the response of larval stages to warming. In species with feeding larvae, warming and food limitation may result in negative (additive or synergetic) effects on growth and survival. We experimentally evaluated the combined effects of temperature and food limitation on larval performance of the invasive crab Hemigrapsus sanguineus (local population of Helgoland, North Sea, German Bight). We then compared the performance of H. sanguineus with the native competitor (shore crab Carcinus maenas). Within the studied temperature range (15-24 °C) and under the conditions of food limitation (access to food for 6 hours a day), the primary driver of survival was temperature (low temperatures decreased survival especially at the more advanced stages). Food limitation decreased survival and growth at all temperatures but larvae metamorphosed to megalopa at all food limited conditions. The response of H. sanguineus differed from that of C. maenas where effects low temperatures have little impact on performance but high temperatures enhance the negative effects of food limitation. Hence, these two coexisting species appear to have different larval responses to warming and food limitation, with warming leading to a higher performance of the invasive relative to the native species.

Larval performance of the exotic Hemigrapsus sanguineus under increased temperature and food limitation

Two rounds of genome duplication (GD) in the ancestor of vertebrates, followed by additional GD during the evolution of ray-finned fishes (Actinopterygii), expanded certain gene families, including those encoding the hypoxia inducible transcription factor (HIF). The present study analyzed Actinopterygian genomes for duplicates of HIFα, the subunit that confers oxygen-dependent gene regulation. In contrast to tetrapod vertebrates that retain three HIFα genes from the ancestral vertebrate GD, four HIFα forms were found in the genomes of primitive Actinopterygians (spotted gar and Asian arowana). All four forms have been retained in zebrafish and related species (Otocephala) and salmonids and their sister taxa (northern pike) but one of them (HIF4α) was lost during the evolution of more derived fishes (Neoteleostei). In addition, the current analyses confirm that Otocephala retain duplicates of HIF1α and HIF2α from the teleost-specific GD, provide new evidence of salmonid-specific duplicates of HIF1α, HIF2α, and HIF3α, and reveal a broad distribution of a truncated form of HIF2α in salmonids and Neoteleostei. This study delivers a comprehensive view of HIFα evolution in the ray-finned fishes, highlights the need for a consistent nomenclature, and suggests avenues for future research on this critical transcription factor.

Genomic Analysis of Hypoxia Inducible Factor Alpha Reveals Missing Ohnologs and Evidence of Widespread Positive Selection in Ray-Finned Fishes

Land plants cover their epidermis with a specialised protective layer called the cuticle, a feature which is crucial for surviving the perils of a terrestrial environment, including desiccation, UV damage and pathogen attack, dangers which may worsen with our escalating climate crisis. Several cereal staples such as barley and wheat show further epidermal specialisation with a distinctive, glaucous wax bloom on reproductive stage tissues, a feature associated with improved drought tolerance. Understanding the mechanisms underpinning wax bloom development may help breed more climate resilient varieties. To date, studies on barley eceriferum mutants have identified several enzymes involved in cuticular wax biosynthesis. However, little is known about the upstream regulation of this process. My research addresses this knowledge gap by exploiting genetic resources to identify a key regulatory player in barley cuticle development. Here, I will discuss how I used high density genotyping, comparative gene expression and wax compositional analyses to identify a gene essential for wax bloom formation and the expression of cuticular metabolic genes in barley.

Identification of a key regulator controlling cuticular wax in barley

Hydrogen peroxide (H2O2) is widely used as a signalling molecule. It is critical to measure H2O2 with a high spatial and temporal resolution to better understand its role as a messenger. The most frequent approach to detect H2O2 has been using chemical probes, which have the disadvantage of limited specificity and cannot report any dynamics or spatial information. Genetically encoded probes have made significant advances to overcome these limitations. Probes of the HyPer family consist of a circularly permuted yellow fluorescent protein (cpYFP) core and a sensing domain from a bacterial H2O2-activated transcription factor (OxyR). These, however, have a pronounced pH sensitivity. Other H2O2 sensors, such as roGFP2-Orp1, have shown to be pH-insensitive but lack the responsiveness to detect low nanomolar H2O2 changes, possibly due to the strong reducing effect of the glutathione redox potential (EGSH). A new ultrasensitive HyPer7 fuses the OxyR of N. meningitidis to an optimized cpYFP largely pH-independent. Here, we have generated and characterized stable Arabidopsis thaliana plants expressing a cytosolic version of HyPer7 and prove that the reduction of this sensor is mostly EGSH-independent and highly responsive to externally imposed oxidation via H2O2 feeding. Furthermore, HyPer7 could sense stress-induced H2O2 in live-cell plants exposed to herbicides, such as methyl viologen or the flagellin-induced apoplastic ROS burst, much better than the previously mentioned H2O2 probes. HyPer7 sensitivity also allowed us to see that the laser light used for excitation is sufficient to induce H2O2 release from chloroplasts in amounts only detected by this ultrasensitive sensor.

The latest HyPe(r) in plant H2O2 biosensing

Membrane trafficking and organelle biogenesis play important roles in plant growth and development, as well as responses to external signals. The plant endomembrane system contains several functionally distinct membrane-enclosed organelles, including the endoplasmic reticulum (ER), Golgi apparatus, trans-Golgi network (TGN) or early endosomes (EE), prevacuolar compartment (PVC) or multivesicular body (MVB) and vacuole. One of our major research programs has been focused on illustrating the underlying mechanisms of vacuolar trafficking and vacuole biogenesis and function in plant cells. One major approach has been the whole-cell electron tomography (ET) analysis with nanometer resolution of vacuole formation and distribution in different cell types of developmental stages, including root cells, stomatal lineage cells and developing pollens in Arabidopsis. Here I will present our recent work and models of vacuole biogenesis and function in plants from the ET analysis. Supported by grants from the Research Grants Council of Hong Kong and CUHK. 

Whole-cell Electron Tomography Analysis of Vacuoles in Plant Cells

Cereal grains are among the most important sources of energy for humans and domestic animals, owing to large and nutritious endosperm tissues. We study nuclear organization and chromatin in seeds of cereals using cultivated barley (Hordeum vulgare subsp. vulgare) - a diploid temperate zone model cereal used for both food and feed. Barley has a large genome (2n = 2x = 14, 1C = 5.1 Gbp) with interphase chromosomes organized in Rabl configuration with centromeres and telomeres clustering at opposite nuclear poles. Though considered to be typical for large cereal genomes, observations of Rabl configuration are based mostly on nuclei from meristematic tissues. We explored interphase chromosome organization in different tissues of developing barley grains and will show that Rabl chromosome organization is not a general rule in barley and it diminishes with the increasing nuclear DNA content and seed age. Furthermore, we performed transcriptome profiling of different barley grain tissues that allowed determining roles of different biological processes and also chromatin regulatory pathways during this critical stage of development. In summary, all these facets of our barley chromatin research create a fruitful environment for future functional analyses of nuclear organization and epigenetic regulation of gene expression in this agriculturally important species.

The dynamics of chromatin changes during barley seed development

Reactive oxygen species (ROS) are by-products of oxidative metabolism, and while low levels contribute to cell signalling, high levels can be toxic. In mammals, ischaemia-reperfusion leads to production of toxic levels of ROS, which cause oxidative tissue damage. In contrast, anoxia-tolerant species, such as the freshwater turtle, do not sustain oxidative tissue damage after anoxia and reoxygenation. How anoxia-tolerant animals are able to prevent ROS dysregulation and oxidative damage with anoxia is unclear. We investigated ROS production and antioxidant capacity in the turtle heart upon anoxia-reoxygenation. Using the in vivo mass-spectrometric H2O2-probe MitoB, we found that there is no excessive production of ROS in the turtle heart after whole animal anoxia-reoxygenation. We hypothesized that this was due to the fact that turtles avoid large accumulation of succinate in the heart and preserve energy levels. This would prevent reverse electron transfer and extensive ROS production from complex I after anoxia. However, addition of exogenous succinate and manipulation of membrane potential with oligomycin did not induce excessive ROS production in turtle heart strips in vitro. This suggests that other factors, such as S-nitrosation of complex I, supercomplex stability or high antioxidant capacity may also be involved in preventing ROS after anoxia in the turtle heart. Together, this study shows that turtles are able to avoid toxic levels of ROS in the heart and oxidative tissue damage after anoxia and reoxygenation. 

Low in vivo production of reactive oxygen species after anoxia and reoxygenation prevents oxidative damage in the turtle heart

Surviving in low oxygen environments requires complex and integrated physiological responses, many of which center on economizing energy budgets. At the cellular level, significant reductions in protein synthesis and even translational arrest (in anoxia) can save as much as 90% of routine ATP demand. This suggests strategic investment in the protein complement of essential tissues, like the heart, that must maintain some level of function for the animal to survive through and recover from a hypoxic bout. The use of quantitative proteomics in animal models of hypoxia tolerance has unveiled new ideas about how the cardiac proteome is influenced by hypoxia exposure, as well as the ontogenic constraints on this aspect of cardiac plasticity. For example, developmental hypoxia exposure of American alligators (Alligator mississippiensis) induces persistent shifts in the cardiac proteome that, paradoxically, reflect an increased capacity for translation, proteolysis, and metabolic capacity. Concomitant with these changes was an equitable down-regulation of seemingly random cardiac proteins, which may offset the cellular energy budget. In Western painted turtles (Chrysemys picta bellii), the cold acclimation required to prepare tissues for chronic anoxia during winter dormancy induced general down-regulation of electron transport system proteins in adult but not hatchling turtles. Interestingly, both studies revealed 
‘age’ as a key explanatory variable in the cardiac proteome. This suggests a robust developmental program in the ectotherm heart that is resilient even to potent environmental stressors like oxygen and temperature, and warrants further investigations into the developmental thresholds of hypoxia tolerance.






Proteomes & Juveniles: A synthesis of ideas on the ontogeny of hypoxia tolerance

There are several pre- and post-natal routes whereby the adverse effect of parental age on offspring longevity (the Lansing effect) could occur, and the nature and magnitude of the effects could also be influenced by environmental factors that affect parent or offspring state. Furthermore, we know little about the extent to which any such effects persist beyond the first generation. In this talk we will describe experiments in which female zebra finches lived in a mildly stressful environment other when they were not breeding. In both young and old age these females bred with young males, thereby controlling for effects of old father age. The telomere length of their offspring at 30 days after hatching was compared with those produced by females that always lived in a benign environment. When the mothers were young, those that had lived in the more stressful environment had sons (but not daughters) with significantly shorter telomere lengths than those of mothers living in the benign environment. Offspring of both sexes had substantially shorter telomere lengths when the mother was old than when she was young. This effect of maternal age on F1 offspring persisted into the F2 generation, with grandmother (F0) age at the time of producing the mother (F1) having a substantial effect on telomere length in the F2 offspring. In contrast, no effect of grandmother environment was evident in the F2 generation. Such maternal and grand-maternal age effects on early life telomere length could underpin the Lansing effect.

Effects of maternal and grandmaternal age at breeding on a biomarker of ageing

It is clear that the age of parents at the time of conception can affect the phenotype of the next generation. The most commonly observed adverse trend is for old parents to produce offspring that have a shorter lifespan (the Lansing effect). Effects such as this are important to our understanding of the selective forces shaping life history evolution, yet we rarely understand the underlying mechanisms, nor whether they actually reduce offspring fitness. For instance, is a shorter lifespan due to greater frailty ( = greater likelihood of dying, even at younger ages) or an earlier onset of senescence, and is it offset (or even caused by) a greater investment by the offspring in early reproduction? In this talk I will outline the potential routes whereby a Lansing effect can occur, and discuss how these might be teased apart through carefully designed experimental studies. I will stress that parental age effects such as the Lansing effect can arise via routes that have nothing to do with biological ageing of the parents or their offspring, since there can be indirect effects of parental age such as changes in investment patterns by their mates. We also need to be aware that there may be compensatory responses by the offspring themselves that obscure the underlying effects of parental age. Consideration of these issues should reveal why phenomena such as the Lansing effect are seen in some contexts and not others.  

Legs as linkages: thinking of isometric muscles and tendons as bicycle spokes

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