Czechia

Adequate oxygen delivery to tissue is important for maintaining cellular homeostasis. Thus, an animal’s ability to detect low oxygen is crucial for survival. In fish, oxygen sensing occurs in the gills via chemoreceptive neuroepithelial cells (NECs). Despite the many similarities between NECs and mammalian chemoreceptors, the receptors and neurochemistry involved in gill hypoxia signalling have not been well defined. The goals of the present study were to delineate a mechanism by which presynaptic dopamine D2 receptors modulate the chemoreceptor response to hypoxia, and to begin exploring receptors involved in the excitatory transmission of hypoxia within the zebrafish gill. Using an isolated gill preparation from Tg(elavl3:GCaMP6s) zebrafish, we found NECs respond to hypoxia by an increase in [Ca2+]i and activation of presynaptic dopamine D2 receptors with the selective agonist, quinpirole, decreased the calcium response to hypoxia. Presynaptic modulation via D2 receptors led to a decrease in the activity of postsynaptic neurons that innervated NECs during hypoxia. Further evaluating the postsynaptic responses to hypoxia, we demonstrated activation of these neurons with acetylcholine, and the neuronal response to hypoxia was reduced by addition of hexamethonium, a nicotinic acetylcholine receptor antagonist. Our results provide the first direct evidence of neuromodulation of the hypoxic signal produced by NECs in the gill by dopamine, suggesting that a modulatory role for dopamine in oxygen sensing arose early in vertebrate evolution. Further, we suggest a role for acetylcholine in the transmission of the hypoxic response, further highlighting the similarity between NECs and mammalian chemoreceptors.

SEB Conference 2024

Chemoreceptor inhibition by dopamine D2 receptors and post synaptic responses to ACh in isolated zebrafish gills.

oxygen sensing

necs

hypoxia

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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.

technical paper

In fishes, the fish pseudobranch is the paired, small hemibranchs of mandibular arch-derived gill tissue. Each pseudobranch receives oxygenated arterial blood and the efferent blood travels to the eyes. In the Nile tilapia (Oreochromis niloticus), the pseudobranch is fully embedded without any freely exposed gill filaments to the water which precludes the typical gill function of gas exchange. The pseudobranch parenchyma cells are rich in mitochondria and have a tubular system similar to gill ionocytes indicating a high metabolic capacity. Despite being identified over 200 years ago, the pseudobranch has remained enigmatic. One hypothesis regarding its function is that it acidifies the blood to aid in oxygen unloading (Root shift) to aid eye oxygen delivery; however, supporting physiological data is lacking. In the present study we used RNAseq to characterize the gene repertoire of the pseudobranch by contrasting expression with gill tissue. We identified 2621 higher and 2502 lower expressed genes (|FC| > 2 p<0.05; PBr:Gill). This notably included higher pseudobranch expression of genes involved in the pentose phosphate shunt, and lactate metabolism as well as ion transport gene isoform differences (eg Na+/K+-ATPase α1a is higher in gill and α1b in pseudobranch). Transporters involved in Na+ uptake (nhe2, ncc2) were higher in gill too. However, the nhe5 was very highly expressed in pseudobranch and using immunohistochemistry Nhe5 was localized to the pillar cells (specialized endothelial cells) of the pseudobranch but not the gills. Together, these results suggest that in tilapia the pseudobranch may be involved in blood acidification.

Elucidating the function of the enigmatic fish pseudobranch using transcriptomics. Novel expression of the Na+/H+-exchanger 5.

Allometry describes how the characteristics of living organisms change with body size. Although a decline in fish size is acknowledged as one of the widespread responses to global warming, relatively few studies have investigated the allometry of thermal limits, and even fewer have attempted to quantify the cardiorespiratory responses that may underlie any size-dependent thermal tolerance.

We measured the allometry of arterial and venous oxygen tension (PaO2 and PvO2) of 65 rainbow trout ranging from 200 to 3800 g across stepwise, acute temperature increases (18, 21.5, and 25°C) and under both normoxia and hyperoxia (150% O2). Additionally, we measured the aerobic metabolic rates of 130 rainbow trout ranging from 10 to 350 g under similar temperature and oxygen regimes.

While PaO2 did not scale with body mass throughout the temperature ramp, oxygen supplementation via hyperoxia lifted overall arterial oxygen tension. Aligning with previous work on salmonids, PvO2 declined with increasing fish size in normoxia, suggesting the potential for cardiac impairments in large individuals. While the mass-dependent decline in PvO2 was attenuated in hyperoxia, thermal limitations were observed without clear correlation to oxygen supply capacity. These findings have implications for the global discussion around climate warming and fish oxygen limitations and highlight the need for a better empirical understanding of size-dependent thermal tolerance.

The allometry of vascular oxygen supply during an acute thermal challenge in rainbow trout

How would you describe the shape of the isometric force-length-activity relation (FLAR) of striated muscle sarcomeres to your students? Simple textbook knowledge, right? At very long lengths, the sarcomere (and thus the whole fiber) is unable to exert any active force even when fully activated. When the sarcomere is gradually held at shorter lengths, the force increases somewhat linearly.
For a certain 'optimal' length -- or 'plateau' region -- the force output reaches its maximum, before it decreases again for even shorter lengths.

When it comes to explaining this shape, the long-length characteristic (the descending branch) is commonly associated with the relative overlap between thin and thick filaments. However, explanations for the force decrease at shorter lengths (the ascending branch) are rather vague. In the literature, there exist several attempts of explaining a piece-wise linear ascending branch by assuming
(i) repelling forces between opposing thin filaments, (ii) thick filament compression at the Z-disk, or (iii) steric hindrance of cross-bridge building. This talk addresses these hypotheses by revealing sources, misconceptions, and counterevidence.
Further, a biophysical model is presented, exploiting know mechanisms such as the volume constancy of the filament lattice, electrostatics-induced cross-bridge building, and Hill's equation of ligand-receptor complexes. A combination of these mechanisms fully explains the experimentally observed FLAR and even pertains to submaximally Calcium-activated fibers -- a realm where conventional approaches struggle.

Biophysical mechanisms underlying the force-length-activity relation of the sarcomere

The body muscles of fish are separated into segments by connective tissue sheets (myosepta) folded into a W-shape of slopes and cones. The biomechanical function of this complex shape is a long-standing question. Current hypotheses link myosepta shape to the magnitude of lateral bending during swimming, with morphological studies focusing on changes in myosepta shape across the mid- and caudal-regions of the body. We know little about how myosepta may contribute to dorsal bending during feeding, and comparative studies of myosepta morphology have been limited by the difficulty of visualising and measuring myosepta shape in 3D. How does myosepta shape vary from head to tail, and among species with differing dorsal bending during feeding? We used contrast-enhanced magnetic resonance imaging (MRI) to visualize cranial, dorsal (epaxial) myosepta in 7 fish species including different body shapes and feeding behaviours. We observed a surprising diversity of shapes across species. The more cranial myosepta of frogfish (Antennarius sp.), anglerfish (Chaenophryne draco), Cape dory (Zeus capensis), and pufferfish (Canthogaster punctissima) were relatively planar and cone-less myosepta, and bisected by a horizontal connective tissue sheet (except in pufferfish). More caudal myosepta in these species and all myosepta in trout (Oncorhynchus mykiss) and killifish (Fundulus parvipinnis) were more typically W-shaped. These results demonstrate myosepta shape can vary substantially across the spine and among species. We hypothesize that planar, cone-less myosepta may allow relatively large, local dorsal bending of the vertebral column. More data are needed to untangle the impact of functional and phylogeny on myosepta shape.

Unexpected diversity in the 3D shape of myosepta in fish body muscles

The force produced by activated skeletal muscle increases considerably (i.e., about 1.5 – 2 times) upon stretching its half sarcomeres a small amount (i.e., about 10 nanometers), and plateaus upon further stretching. Similar force transients can be observed across a broad range of stretch velocities, and across a broad range of species. The initial rise in force is known as short-range-stiffness and is believed to help stabilize animal movements by reducing the need for neural control. Short-range-stiffness is difficult to assess during movements but could be predicted using computer simulations with musculoskeletal models. However, current simulations rely on phenomenological Hill-type muscle models, which cannot explain history-dependent changes in short-range-stiffness with prior shortening, that may occur during movements. In contrast, simple biophysical muscle models have history dependence, but cannot reproduce force transients during stretch. This may be because such simple models typically only have one bound and one unbound crossbridge state, while experimental data suggest that crossbridges have at least two bound states (e.g., weakly or strongly) and two unbound states (e.g., detached or forcibly detached). Complex biophysical models including such states have previously been shown to fit force transients better, but at a high computational cost. To facilitate implementing such models in musculoskeletal simulations, we therefore applied a moment approximation to their crossbridge distributions and greatly reduced their computational cost. These models reproduced both force transients and typical steady-state force-velocity relations for various muscles. Ultimately, we will implement biophysical muscle models in musculoskeletal simulations to elucidate how muscle properties shape movement biomechanics.

A simple biophysical muscle model explains force transients during lengthening

Ectotherms can regulate their body temperature by moving between cooler and warmer environments. The choice of a thermal environment can be driven by different parameters, including an individual’s health status. For instance, disease and parasite infection can cause some species of fish to increase their body temperature by spending more time in warmer waters, presumably to maximise their immune defences and, thus, the chance to fight off the infection, a phenomenon known as behavioural fever. Most studies on fish thermoregulation do not consider how the immune response to disease and/or parasite infection can shape a fish’s thermal choice. Yet, the severity of the parasite infection (load), the presence of multiple parasite species (co-infection) and the timing of the infection (acute vs. chronic) can change temperature preference. Here, we measured the preferred temperature of wild-caught pumpkinseed sunfish using a shuttle-box system. Fish were separated into three groups: 1) chronically co-infected by parasite, 2) acutely exposed to parasite, and 3) immune-stimulated via injection of lipopolysaccharide (LPS) endotoxin. We observed that the fish’s preferred temperature did not vary with parasite infection,co-infection and immune-stimulation. This suggests that fish did not display behavioural fever. This combination of groups with different infection status allowed us to tease apart the role of the immune system in thermal choice and deepen our understanding of animal movement. Ultimately, this helps our comprehension of how ectotherms fight disease in nature.

Temperature preference in immune-stimulated and parasite-infected sunfish

At Nottingham Trent University (NU) we have established a Biosciences Employer Advisory Group who inform our curriculum and assessment practice thereby ensuring our graduates are work ready and possess the skills the industries require now and in future. 

Our employers are directly involved in delivering session to our students, interacting with our students and feed back on their skillset and competencies. Employers are involved in showcasing their work processes, industry expectations, professional expectations across a range of skillsets such as competency testing and sign off, interview techniques and job applications, Biochemistry assays and applications and the use of genetic testing to name just a view. 

This has involved adapting module delivery, teaching activities and new assessments to mimic work activities and re-create work scenarios. During the process students develop critical thinking, problem-solving, and communication skills relevant to their future careers. 

The implementation is not without challenges including sustainability resource limitations, academic team buy-in, and logistical constraints. Addressing these challenges requires ongoing evaluation and adaptation of our initiative, alongside institutional support. 

The recreated employment experiences in bioscience education offers numerous benefits for students, educators, and employers alike. By aligning assessments with real-world work activities, fostering industry partnerships, and promoting student engagement, students on full time modes of study are prepared for successful careers in the bioscience field.

Ensuring work readiness of BSc (Honours) Biochemistry graduates at NTU through employer led assessment practice

This talk will cover the emerging field of Scholarship of Teaching and Learning (SoTL). The session begins by introducing SoTL models and definitions, and the integration of practice and theory. It will then explore some practical strategies to develop a scholarly approach to teaching and outreach. 

This session is relevant to anyone who is on a teaching and scholarship career track, or is interested in developing their expertise in Scholarship of Teaching and Learning, and links to teaching in higher education.

An Introduction to Scholarship of Teaching and Learning for Bioscientists

Ensuring food security for an ever-growing global population while adapting to climate change is the main challenge for agriculture in the 21st century. The gene discovery pipeline BREEDIT, combines multiplex genome editing with crossing schemes to improve complex traits such as yield and drought tolerance. During the presentation, I will explain different use cases of the BREEDIT technology, while I will also highlight how it brings together genomics, transcriptomics, phenotyping and machine learning.

Multiplex genome editing strategies to assess the combinatorial potential of yield contributing alleles in maize

Reproductive ageing is intrinsically linked with the interactions
between the germline and the soma, where germline maintenance
appears to come at the cost of somatic ageing. Signalling pathways
determine the level of cellular and genome maintenance in
the germline and the soma. Because germline maintenance is
predicted to be costly, the allocation to germline maintenance
may vary throughout an organism’s life resulting from the putative
trade-off between somatic maintenance, offspring number and
offspring quality through the production of high-quality gametes
carrying healthy genomes. Males appear to be particularly
vulnerable to sub-optimal germline maintenance and germline
ageing as spermatogenesis continues throughout life and involves
continuous mitotic and meiotic divisions for tissue proliferation.
We tested the germline-soma interactions in male zebrafish
Danio rerio using knockdown and knockout to generate germlinefree
fish and compare somatic responses to genotoxic stress in
germline-free and germline-carrying males. We also performed
mutation accumulation experiments using the nematode
Caenorhabditis remanei to assess germline mutation rates as an
indicator of germline maintenance in young, peak reproductionaged
and old worms. All our experiments hint at a tight regulation
and interaction between germline and soma and I will discuss our
results in the light of the expensive germline hypothesis and its role
in reproductive ageing.

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Next from SEB Conference 2024

Elucidating the function of the enigmatic fish pseudobranch using transcriptomics. Novel expression of the Na+/H+-exchanger 5.

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Plasticity in respiratory traits and stable hypoxia tolerance in a weakly electric fish exposed to long-term changes in dissolved oxygen environment

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Next from SEB Conference 2024

Elucidating the function of the enigmatic fish pseudobranch using transcriptomics. Novel expression of the Na+/H+-exchanger 5.

Similar lecture

Plasticity in respiratory traits and stable hypoxia tolerance in a weakly electric fish exposed to long-term changes in dissolved oxygen environment

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