Czechia

Maintaining pH homeostasis is not only require for the biomineralization process of marine calcifiers but also essential to their adaptation streitige against the environmental challenge such as ocean acidification. The calcareous endoskeleton of sea urchin larva, which benefits from years development of gene regulatory networks, ex vivo tissue engineering technique and in vivo gene manipulation approaches, becomes a powerful model for biomineralization research. Based on the model organism Strongylocentrotus purpuratus, our research group discovered a serial transporters and enzymes that are critical to cytosolic pH (pHi) regulation in skeletogenic cells. The cytosolic bicarbonate sensor soluble adenylyl cyclase (sAC) is one of these factors which might play the central role regulating intracellular pH homeostasis. The cAMP signaling triggered by activated sAC may further stimulates the channel activity and gene expression of pH effectors in skeletogenic cell. In order to investigate the interaction between cAMP signaling and pH-regulating transporters, we developed skeletogenic cell-specific gene expression approaches. According to our preliminary results, the activity of sAC is possibly regulated through its alternative splicing, and the splicing event is stimulated by skeleton regeneration. Further evidences are required to clarify the regulation of sAC splicing event and cytosolic pH homeostasis that initiated by cAMP signaling. The present study demonstrates a canonical cellular stress response that a sensory factor reacts to environmental stimulation through post-transcriptional modification.

SEB Conference 2024

Soluble adenylyl cyclase regulates intracellular pH homeostasis of calcifying cells in the sea urchin larva.

ph homeostasis

soluble adenylyl cyclase

biomineralization

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For decades marine biologists and earth scientists have wanted to understand how changes in the seawater environment affect coral skeleton growth. That’s because coral calcification builds ecologically important coral reef structures and coral skeletons contain chemical signatures used as recorders of climate. The growth front of the coral skeleton does not come into direct contact with seawater, but instead forms in an extracellular calcifying medium (ECM) controlled by a specialised cell layer called the calcifying ‘calicoblastic’ epithelium. Unravelling the physiology of this calcifying epithelium (and coral physiology in general) is key to understanding why coral calcification responds to environment change. This challenge is an important focus of research at the Centre Scientifique de Monaco (CSM). Using an innovative coral sample preparation in controlled environmental experiments, we carry out in vivo physiological studies using a range of tools including confocal microscopy coupled with physiological indicator dyes and microelectrodes. This research has provided insight into regulation of pH, calcium and dissolved inorganic carbon concentration of the ECM by transcellular transport via the calicoblastic cells. We have also conducted investigations of paracellular transport to better understand how permeability of the calicoblastic epithelium determines exchange of ions and molecules between seawater and the ECM. We also investigate the impact of ocean acidification on these physiological parameters. Overall, our in vivo physiological data complement information arising from ‘omics’ studies on corals at CSM and other laboratories and helps us move towards a clearer understanding of coral calcification in a rapidly changing ocean.

An engineering epithelium: ion transport and pH regulation of the calcifying cell layer of reef-building corals

Dissolved oxygen is a key environmental parameter for aquatic life. In two sets of experiments we evaluated the effect of long-term changes in the dissolved oxygen environment on the morpho-physiology and behaviour of the weakly electric fish Petrocephalus degeni. First, we captured fish from a severely hypoxic habitat in Uganda and acclimated them to normoxic conditions for up to 73 days while measuring respirometric and morpho-physiological traits in the field. In the second experiment, we used fish that had been kept under normoxic conditions for over two years in the laboratory. We assessed their hypoxia avoidance behaviour as well as physiological traits before and after 56 days of exposure to hypoxic conditions (15% air saturation). We found that gill size changed significantly in both experiments. Blood haemoglobin concentration was only affected during normoxia acclimation. Other traits, such as critical oxygen tension and hypoxia avoidance behaviour, were unaffected by the acclimation treatment. Our results suggest that P. degeni remain remarkably hypoxia tolerant throughout acclimation to different oxygen environments. Plasticity in respiratory traits that are directly associated with oxygen extraction and carrying capacity likely facilitates the homeostasis of higher-level traits linked to hypoxia tolerance, such as critical oxygen tension and hypoxia avoidance, by optimizing energetic trade-offs in different dissolved oxygen environments.

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

The ubiquitous presence of microplastics (MPs) in aquatic ecosystems is a growing concern. The ability to adsorb a variety of pollutants on its surface, including heavy metals, accentuates the magnitude of its impacts. The widespread contamination by MPs highlights the need to investigate the toxicological interactions of these polymers with heavy metals. Besides, there is still a gap in knowledge regarding the toxic effects of this mixture on microbiological interactions.
This study intended to evaluate the combined effects of MPs and copper on the intestinal microbiota. Polyethylene (PE) and polystyrene (PS) MPs were selected because of their extensive use and high accumulation in aquatic environments. For this, zebrafish (Danio rerio) were exposed for 21 days, to copper (Cu-25 μg/L), microplastics (PE and PS, 1mg/L), and the respective mixtures (PE-Cu and PS-Cu), to evaluate their effect on the intestinal wall ultrastructure and the intestinal microbiota.
The histopathological evaluation revealed changes, including necrosis, degeneration of intestinal folds, edema, infiltration of inflammatory cells, and goblet cells hyperplasia. Considering the intestinal microbiota, P. shigelloides was the microorganism present in the highest percentage (47%) and a multidrug resistance profile was observed in 67.6% of the isolated microorganisms. The highest resistance rates were observed in response to β lactam antibiotics, aminoglycosides, and tetracyclines.
This work has provided valuable insights into the intricate interaction between MPs and copper in the induction of histological changes, and antibiotic susceptibility.

This work is supported by National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020.

Gut microbiota and antibiotic susceptibility profile: combined effect of microplastics and copper in zebrafish (Danio rerio)

Drivers of large variation in observed fish growth, even under controlled conditions such as in aquaculture experiments, are not well understood. Size-based intraspecific competition is known to influence processes which lead to variation in both intake and growth. Yet, it is challenging to tease apart the effects of competitive interactions on fish growth from those of other factors because it remains difficult to repeatedly measure the relevant components of individual fish physiology that contribute to growth. We used an extensive longitudinal dataset of individual-level intake and growth measurements of 543 fish sampled from an aquaculture experiment to test the effects of relative body size as a proxy for competitive ability. This, in turn, was investigated as potential modulator of both individual feed intake and costs of living inferred from growth in a bioenergetic model. Using a Bayesian approach to integrate data and model, we estimated the mass-dependent scaling of intake and costs of living. Including relative size-effects on the allometric relationships for both intake and costs of living improved model fit and allowed us to reproduce a large part of the observed size variation. This implies that size-dependent competitive interactions are an important driver of size-at-age variation. Our results also indicate that growth depression in smaller than average fish is more significantly impacted by size-based competition effects on costs of living rather than on feed intake.

Size-based competition explains large variation in both intake and growth in aquaculture experiment

Cell division plane (CDP) orientation and cell growth directionality, determine tissue patterning and organ formation. A core component of CDP orientation is the preprophase microtubule band (PPB). It is known that PPB is physically associated with the plasma membrane (PM) requiring recruitment of scaffold proteins with affinity towards specific PM lipids and for proteins associated with microtubules. The mechanisms underlying the determination of CDP orientation are being vigorously studied. Yet, the specific identity and the role of PM lipids in the recruitment of scaffold proteins remain elusive. Sterols, a major lipid group forming nanodomains at the PM, play vital roles in cellular processes such as endocytosis, cell polarity and, cell expansion. Moreover, early studies on Arabidopsis sterol biosynthesis mutants have described severe developmental defects. However, no mechanism of implication of sterol biosynthesis deficiency in the determination of cell division has yet been proposed. Here, we have revisited the role of structural sterol biosynthesis on Arabidopsis vegetative growth and tissue patterning, as contrasted defects arising from compromised production of brassinosteroids, focusing on how CDP specific microtubule arrays are formed. Sterol biosynthesis mutants cpi1-1 and smt2smt3 showed defective vegetative phenotypes and disrupted histological pattern, as exemplified in the root. Aberrant mitosis with ectopic cell divisions. The smt2smt3 showed more severe phenotype than cpi1-1 indicating a possible role of structural phytosterols in the determination of CDP. Pharmacological treatments with sterol biosynthesis inhibitors phenocopied the sterol biosynthesis mutants. To conclude, cell division abnormalities are due to sterol biosynthesis pathway rather than brassinosteroids biosynthesis.

Impairment of sterol biosynthesis affects cell division and cell division plane orientation

Awarding gaps are differences in degree classification between demographic groups. In the UK there are known awarding gaps on the basis of ethnicity, socioeconomic status, age and disability. Progress on closure of gaps is notoriously slow, with inequity persisiting year after year. In this presentation I will explore the potential of innovative assessment in closing gaps. At the University of Hull we have made significant progress in closing awarding gaps, primarily through an institution wide focus on innovative, authentic competency based assessment. I will give an overview of this at institution level and within the biosciences, and provide practical suggestions for equitable assessment design

Closing Awarding Gaps through Innovative Assessment: A whole university approach

The Arabidopsis genome contains genes encoding High Mobility Group (HMG) chromatin remodelers which function as transcription activators crucial for transcription of a plethora of genes. AtHMGB15, an ARID-HMG protein that harbors an AT rich interaction domain along with the classic HMG-Box DNA binding domain exhibits heightened expression primarily in flowers and pollen grains. The intricate process of male gametophyte development in flowering plants is regulated by jasmonic acid (JA) signaling. JA signalling initiates with the activation of MYC2 transcription factor, leading to the expression of numerous JA-responsive genes during stamen development, and pollen maturation. 

This study investigates the broader molecular analysis and biological relevance of transcriptional regulation of AtHMGB15 in orchestrating pollen development via the hormone pathway. Phenotypic characterization of athmgb15-4 mutant plants revealed delayed bolting, shorter siliques, and reduced seed set compared to the wildtype. Additionally, the mutation of AtHMGB15 resulted in defective pollen morphology, delayed pollen germination, aberrant pollen tube growth, and a higher percentage of non-viable pollen grains. In silico and molecular analysis validated the down-regulation of JA biosynthesis and signaling genes in the athmgb15-4 mutant. Quantitative analysis demonstrated that jasmonic acid and its derivatives were approximately tenfold lower in athmgb15-4 flowers. Exogenous application of methyl jasmonate could restore pollen morphology and germination alongside elevating the expression of previously down-regulated JA signaling genes, suggesting that the low jasmonate content in athmgb15-4 impaired JA signaling during pollen development. Furthermore, our study suggests that AtHMGB15 physically interacts with the MYC2 protein to form a transcription activation complex further promoting the transcription of two key JA signaling genes, namely MYB21 and MYB24, during stamen, and pollen development. 

We thereby propose the quintessential role of AtHMGB15 as a positive regulator of JA pathway, controlling the spatial, and temporal expression of key regulators involved in stamen and pollen development.

(Sachdev et. al., Plant Physiology 2024)


Deciphering AtHMGB15, an ARID-HMG Protein in Arabidopsis: Orchestrating the JA Pathway Through MYC2 Regulation in Pollen Development.

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. 

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, we found that a region of chromosome 3 where was inheritance solely from the Col-0 parent. This region contains the gene IBM1, for which transgenerational deleterious effects has been previously associated with change in intronic methylation, leading to alternative splicing of the IBM1 transcript and ectopic genomic hypermethylation occurring at gene bodies. 
In the same regions we also found another gene, a vacuolar ATPase (VHA), had a similar methylation profile to IBM1 and complementary expression within the flower. We hypothesized that the interaction of IBM1 and VHA could explain the transgenerational decrease in fitness observed in met1-3 plants. Existing RNA-seq data was assessed for this possibility, 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


Interaction of IBM1 and a vacuolar ATPase in flowers may explain transgenerational instability of hypomethylated lines

Telomere length in early life is predictive of longevity in many species and reduced early life telomere length in offspring of older mothers has been linked to the reduced longevity frequently found in offspring of older breeders (the Lansing Effect). It is currently unknown whether such telomere reduction may persist beyond a single generation, as would be the case if germline transmission is involved. To test this, we performed a within-grandmother, multi-generational study using zebra finches. Our results indicate that shorter telomeres persist in offspring whose grandmothers were old at the time of their mother´s birth, despite their mother having been a young breeder. Our data highlight the need to look beyond a single generation to explain the causes of inter-individual variation in ageing rates and optimal reproductive schedules.

Negative effects of maternal age at breeding on offspring telomere length persist across twogenerations

In wild vertebrates, age has a strong influence on individual reproductive performance. Specifically, young parents are less likely to successfully rear offspring relative to older ones because of lower parental skills, lower parental investment or because of a progressive disappearance of lower-quality individuals at young ages (i.e., according to the constraint, restraint and selection hypotheses respectively). Such phenomenon has been extensively studied through reproductive success’ features. However, to better evaluate the influence of age on reproductive performance in species with high reproductive success, assessing also the quality of developmental conditions and offspring phenotype appears crucial. While it is practically difficult to follow an offspring during its entire life, several proxies of nestlings’ quality can be useful to assess the ability of young to survive and recruit into the population (i.e., body condition, corticosterone levels, and telomere length). By sampling chicks reared by known-aged mothers, we specifically investigated the influence of maternal age on offspring quality in two long-lived seabird species, the Black-browed Albatross (Thalassarche melanophrys) and the Snow Petrel (Pagodroma nivea). In both species, maternal age is correlated to proxies of offspring quality. More precisely, older individuals provide better parental cares to their offspring. In the light of the three age-related improvement of reproductive performance hypotheses, our results suggest that maternal age can affect offspring phenotype with potential long-term consequences.

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An engineering epithelium: ion transport and pH regulation of the calcifying cell layer of reef-building corals

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The calcification process in sea urchin larvae: insights into pH regulation mechanisms in intracellular vesicles of primary mesenchyme cells (PMCs)

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An engineering epithelium: ion transport and pH regulation of the calcifying cell layer of reef-building corals

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The calcification process in sea urchin larvae: insights into pH regulation mechanisms in intracellular vesicles of primary mesenchyme cells (PMCs)

Stay up to date with the latest Underline news!

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