H(+)/K(+) ATPase activity is required for biomineralization in sea urchin embryos

Embryo-Fetal Developmental Toxicity and Toxicokinetics Studies of YWS1903, a Novel Potassium-Competitive Acid Blocker, in Pregnant Rats

BACKGROUND

In this study, we investigated the developmental and reproductive toxicity of YWS1903, a novel potassium-competitive acid blocker, in pregnant Sprague-Dawley rats.

METHODS

YWS1903 was administered orally at doses of 0 (control), 20, 60, and 200 mg kg-1 from gestation days 6 to 17 (n = 24 per group). Concurrent toxicokinetic analysis was conducted to characterize the toxicokinetic profile and placental transfer of YWS1903.

RESULTS

Aside from hair loss at the highest dose, no significant maternal toxicity was observed up to 200 mg kg-1. Fetal assessments revealed reductions in body weight and crown-rump length at 200 mg kg-1, alongside increased skeletal malformations, but no visceral abnormalities were detected. Toxicokinetic linearity studies revealed that within the 20-200 mg kg-1 dose range, both Cmax and AUC0-t of YWS1903 exhibited disproportionate increases following initial and final administrations. In the high-dose group, the escalation in AUC0-t substantially exceeded the corresponding dose changes, suggesting potential saturation of metabolic pathways at higher exposure levels. YWS1903 was shown to cross the placenta, although fetal plasma concentrations were consistently lower than maternal levels, suggesting reduced direct fetal exposure.

CONCLUSION

The no observed adverse effect level was established at 60 mg kg-1, supporting the compound's safety at moderate doses. These findings provide valuable insights into YWS1903's developmental and reproductive safety profile and offer reference for its clinical application as a therapeutic agent for gastroesophageal reflux disease.

CMTM4 is an adhesion modulator that regulates skeletal patterning and primary mesenchyme cell migration in sea urchin embryos

MARVEL proteins, including those of the CMTM gene family, are multi-pass transmembrane proteins that play important roles in vesicular trafficking and cell migration; however, little is understood about their role in development, and their role in skeletal patterning is unexplored. CMTM4 is the only CMTM family member found in the developmental transcriptome of the sea urchin Lytechinus variegatus. Here, we validate that LvCMTM4 is a transmembrane protein and show that perturbation of CMTM4 expression via zygotic morpholino or mRNA injection perturbs skeletal patterning, resulting in loss of secondary skeletal elements and rotational defects. We also demonstrate that normal levels of CMTM4 are required for normal PMC migration and filopodial organization, and that these effects are not due to gross mis-specification of the ectoderm. Finally, we show that CMTM4 is sufficient to mediate mesenchymal cell-cell adhesion. Taken together, these data suggest that CMTM4 controls PMC migration and biomineralization via adhesive regulation during sea urchin skeletogenesis. This is the first discovery of a functionally required adhesive gene in this skeletal patterning system.

Complement Cross Talks With H-K-ATPase to Upregulate Runx2 in Human Aortic Valve Interstitial Cells

INTRODUCTION

Calcific aortic valve disease (CAVD) is a slowly progressive fibro-calcific valve leaflet disorder. The underlying pathophysiology is complex and not yet well understood. Complement is known to play a role in the pathogenesis of CAVD by upregulating Runx2 to induce profibrogenic change in human aortic valve interstitial cells (AVICs). Furthermore, H-K-ATPase has independently been shown to induce tissue calcification. Therefore, we hypothesized that complement cross talks with H-K-ATPase to upregulate Runx2 in human AVICs.

MATERIALS AND METHODS

Human AVICs were isolated from normal and calcified aortic valves. Cells were treated with a variation of complement, H-K-ATPase, or ERK1/2 inhibitors. H-K-ATPase and its association with complement in AVICs were investigated by reverse transcriptase-polymerase chain reaction, immunofluorescence, and Western blot.

RESULTS

Calcified human AVICs expressed significantly higher H-K-ATPase level than normal human AVICs. Presence of complement C3 with H-K-ATPase is found in AVICs after complement treatment. Complement induced both H-K-ATPase and Runx2 expression in AVICs, which was associated with increased phosphorylation of ERK1/2 and its downstream molecule p-70 S6. Pharmacological inhibition of either H-K-ATPase or Erk1/2 abolished complement-induced Runx2 expression.

CONCLUSIONS

These findings indicate that complement cross talks with H-K-ATPase to upregulate Runx2 in human AVICs by activation of ERK1/2 signaling pathways. The study revealed the potential role of H-K-ATPase in the pathogenesis of CAVD and therapeutically targeting either complement system or H-K-ATPase may limit the development of CAVD.

Polychrome labeling reveals skeletal triradiate and elongation dynamics and abnormalities in patterning cue-perturbed embryos

The larval skeleton of the sea urchin Lytechinus variegatus is an ideal model system for studying skeletal patterning; however, our understanding of the etiology of skeletal patterning in sea urchin larvae is limited due to the lack of approaches to live-image skeleton formation. Calcium-binding fluorochromes have been used to study the temporal dynamics of bone growth and healing. To date, only calcein green has been used in sea urchin larvae to fluorescently label the larval skeleton. Here, we optimize labeling protocols for two additional calcium-binding fluorochromes: xylenol orange and calcein blue- and demonstrate that these fluorochromes can be used individually or in nested pulse-chase experiments to understand the temporal dynamics of skeletogenesis and patterning. Using a pulse-chase approach, we show that the initiation of skeletogenesis begins around 15 h post fertilization. We also assess the timing of triradiate formation in embryos treated with a range of patterning perturbagens and demonstrate that triradiate formation is delayed and asynchronous in embryos ventralized via treatment with either nickel or chlorate. Finally, we measure the extent of fluorochrome incorporation in triple-labeled embryos to determine the elongation rate of numerous skeletal elements throughout early skeletal patterning and compare this to the rate of skeletal growth in embryos treated with axitinib to inhibit VEGFR. We find that skeletal elements elongate much more slowly in axitinib-treated embryos, and that axitinib treatment is sufficient to induce abnormal orientation of the triradiates.

Ethanol exposure perturbs sea urchin development and disrupts developmental timing

Ethanol is a known vertebrate teratogen that causes craniofacial defects as a component of fetal alcohol syndrome (FAS). Our results show that sea urchin embryos treated with ethanol similarly show broad skeletal patterning defects, potentially analogous to the defects associated with FAS. The sea urchin larval skeleton is a simple patterning system that involves only two cell types: the primary mesenchymal cells (PMCs) that secrete the calcium carbonate skeleton and the ectodermal cells that provide migratory, positional, and differentiation cues for the PMCs. Perturbations in RA biosynthesis and Hh signaling pathways are thought to be causal for the FAS phenotype in vertebrates. Surprisingly, our results indicate that these pathways are not functionally relevant for the teratogenic effects of ethanol in developing sea urchins. We found that developmental morphology as well as the expression of some ectodermal and PMC genes was delayed by ethanol exposure. Temporal transcriptome analysis revealed significant impacts of ethanol on signaling and metabolic gene expression, and a disruption in the timing of GRN gene expression that includes both delayed and precocious gene expression throughout the specification network. We conclude that the skeletal patterning perturbations in ethanol-treated embryos likely arise from a loss of temporal synchrony within and between the instructive and responsive tissues.

Carbonic anhydrases in development: morphological observations and gene expression profiling in sea urchin embryos exposed to acetazolamide

Carbonic anhydrases (CANs) are conserved metalloenzymes catalysing the reversible hydration of carbon dioxide into protons and bicarbonate, with important roles in cells physiology. Some CAN-coding genes were found in sea urchin genome, although only one involved in embryonic skeletogenesis was described in Paracentrotus lividus. Here, we investigated gene expression patterns of P. lividus embryos cultured in the presence of acetazolamide (AZ), a CAN inhibitor, to combine morphological defects with their molecular underpinning. CAN inhibition blocked skeletogenesis, affected the spatial/temporal expression of some biomineralization-related genes, inhibited embryos swimming. A comparative analysis on the expression of 127 genes in control and 3 h/24 h AZ-treated embryos, using NanoString technology, showed the differential expression of genes encoding for structural/regulatory proteins, with different embryonic roles: biomineralization, transcriptional regulation, signalling, development and defence response. The study of the differentially expressed genes and the signalling pathways affected, besides in silico analyses and a speculative 'interactomic model', leads to predicting the presence of various CAN isoforms, possibly involved in different physiological processes/activities in sea urchin embryo, and their potential target genes/proteins. Our findings provide new valuable molecular data for further studies in several biological fields: developmental biology (biomineralization, axes patterning), cell differentiation (neural development) and drug toxicology (AZ effects on embryos/tissues).

Cellular bicarbonate accumulation and vesicular proton transport promote calcification in the sea urchin larva

The sea urchin embryo develops a calcitic endoskeleton through intracellular formation of amorphous calcium carbonate (ACC). Intracellular precipitation of ACC, requires [Formula: see text] concentrating as well as proton export mechanisms to promote calcification. These processes are of fundamental importance in biological mineralization, but remain largely unexplored. Here, we demonstrate that the calcifying primary mesenchyme cells (PMCs) use Na+/H+-exchange (NHE) mechanisms to control cellular pH homeostasis during maintenance of the skeleton. During skeleton re-calcification, pHi of PMCs is increased accompanied by substantial elevation in intracellular [Formula: see text] mediated by the [Formula: see text] cotransporter Sp_Slc4a10. However, PMCs lower their pHi regulatory capacities associated with a reduction in NHE activity. Live-cell imaging using green fluorescent protein reporter constructs in combination with intravesicular pH measurements demonstrated alkaline and acidic populations of vesicles in PMCs and extensive trafficking of large V-type H+-ATPase (VHA)-rich acidic vesicles in blastocoelar filopodial cells. Pharmacological and gene expression analyses underline a central role of the VHA isoforms Sp_ATP6V0a1, Sp_ATP6V01_1 and Sp_ATPa1-4 for the process of skeleton re-calcification. These results highlight novel pH regulatory strategies in calcifying cells of a marine species with important implications for our understanding of the mineralization process in times of rapid changes in oceanic pH.

Embryo, larval, and juvenile staging of Lytechinus pictus from fertilization through sexual maturation

BACKGROUND

Sea urchin embryos have been used for more than a century in the study of fertilization and early development. However, several of the species used, such as Strongylocentrotus purpuratus, have long generation times making them suboptimal for transgenerational studies.

RESULTS

Here, we present an overview of the development of a rapidly developing echinoderm species, Lytechinus pictus, from fertilization through sexual maturation. When grown at room temperature (20°C) embryos complete the first cell cycle in 90 minutes, followed by subsequent cleavages every 45 minutes, leading to hatching at 9 hours postfertilization (hpf). The swimming embryos gastrulate from 12 to 36 hpf and produce the cells which subsequently give rise to the larval skeleton and immunocytes. Larvae begin to feed at 2 days and metamorphose by 3 weeks. Juveniles reach sexual maturity at 4 to 6 months of age, depending on individual growth rate.

CONCLUSIONS

This staging scheme lays a foundation for future studies in L. pictus, which share many of the attractive features of other urchins but have the key advantage of rapid development to sexual maturation. This is significant for multigenerational and genetic studies newly enabled by CRISPR-CAS mediated gene editing.

Molecular mechanisms of biomineralization in marine invertebrates

Much recent marine research has been directed towards understanding the effects of anthropogenic-induced environmental change on marine biodiversity, particularly for those animals with heavily calcified exoskeletons, such as corals, molluscs and urchins. This is because life in our oceans is becoming more challenging for these animals with changes in temperature, pH and salinity. In the future, it will be more energetically expensive to make marine skeletons and the increasingly corrosive conditions in seawater are expected to result in the dissolution of these external skeletons. However, initial predictions of wide-scale sensitivity are changing as we understand more about the mechanisms underpinning skeletal production (biomineralization). These studies demonstrate the complexity of calcification pathways and the cellular responses of animals to these altered conditions. Factors including parental conditioning, phenotypic plasticity and epigenetics can significantly impact the production of skeletons and thus future population success. This understanding is paralleled by an increase in our knowledge of the genes and proteins involved in biomineralization, particularly in some phyla, such as urchins, molluscs and corals. This Review will provide a broad overview of our current understanding of the factors affecting skeletal production in marine invertebrates. It will focus on the molecular mechanisms underpinning biomineralization and how knowledge of these processes affects experimental design and our ability to predict responses to climate change. Understanding marine biomineralization has many tangible benefits in our changing world, including improvements in conservation and aquaculture and exploitation of natural calcified structure design using biomimicry approaches that are aimed at producing novel biocomposites.

The developmental transcriptome for Lytechinus variegatus exhibits temporally punctuated gene expression changes

Embryonic development is arguably the most complex process an organism undergoes during its lifetime, and understanding this complexity is best approached with a systems-level perspective. The sea urchin has become a highly valuable model organism for understanding developmental specification, morphogenesis, and evolution. As a non-chordate deuterostome, the sea urchin occupies an important evolutionary niche between protostomes and vertebrates. Lytechinus variegatus (Lv) is an Atlantic species that has been well studied, and which has provided important insights into signal transduction, patterning, and morphogenetic changes during embryonic and larval development. The Pacific species, Strongylocentrotus purpuratus (Sp), is another well-studied sea urchin, particularly for gene regulatory networks (GRNs) and cis-regulatory analyses. A well-annotated genome and transcriptome for Sp are available, but similar resources have not been developed for Lv. Here, we provide an analysis of the Lv transcriptome at 11 timepoints during embryonic and larval development. Temporal analysis suggests that the gene regulatory networks that underlie specification are well-conserved among sea urchin species. We show that the major transitions in variation of embryonic transcription divide the developmental time series into four distinct, temporally sequential phases. Our work shows that sea urchin development occurs via sequential intervals of relatively stable gene expression states that are punctuated by abrupt transitions.

Effects of Ivermectin Exposure on Regeneration of D. dorotocephala Planaria: Exploiting Human-Approved Ion Channel Drugs as Morphoceuticals

Transformative applications in regenerative medicine await increased control of processes implementing repair and remodeling of complex living structures. Recent work reveals ion channel drugs as a powerful toolkit for modulating endogenous bioelectric circuits that control growth and form in vivo and in vitro. It is therefore especially important to develop assays in model systems that will enable the testing of these "morphoceuticals"-compounds with predictable effects on anatomical structure. The regenerative planaria are an ideal model system for this purpose. Several studies have shown a role for bioelectric signaling in planarian regeneration, but these have focused on Dugesia japonica and Schmidtea mediterranea. It is not known how the alterations of ion channel activity would affect regeneration in other species of planaria-an important aspect of building robust computational models of bioelectric circuits. Here, the effect of ivermectin (IVM), a chloride channel opener drug commonly used to combat heartworm is tested, on regeneration in a new species of planaria: Dugesia dorotocephala. Exposure to IVM during regeneration results in patterning abnormalities, such as bifurcated tails with partial heads, as well as delayed regeneration. These data extend our understanding of the effects of human-approved ion channel drugs on regenerative processes.

A SLC4 family bicarbonate transporter is critical for intracellular pH regulation and biomineralization in sea urchin embryos

Efficient pH regulation is a fundamental requisite of all calcifying systems in animals and plants but with the underlying pH regulatory mechanisms remaining largely unknown. Using the sea urchin larva, this work identified the SLC4 HCO₃^- transporter family member SpSlc4a10 to be critically involved in the formation of an elaborate calcitic endoskeleton. SpSlc4a10 is specifically expressed by calcifying primary mesenchyme cells with peak expression during de novo formation of the skeleton. Knock-down of SpSlc4a10 led to pH regulatory defects accompanied by decreased calcification rates and skeleton deformations. Reductions in seawater pH, resembling ocean acidification scenarios, led to an increase in SpSlc4a10 expression suggesting a compensatory mechanism in place to maintain calcification rates. We propose a first pH regulatory and HCO₃^- concentrating mechanism that is fundamentally linked to the biological precipitation of CaCO₃. This knowledge will help understanding biomineralization strategies in animals and their interaction with a changing environment.

Many marine organisms such as mussels, sea urchins or corals, have skeletons and shells, which – due to their beautiful colors and shapes – are often desirable collector pieces. These structures are made from calcium and carbonate ions that react to form calcium carbonate crystals in a process known as biomineralization.

In sea urchin larvae, for example, the skeleton is built by so-called primary mesenchyme cells, which work similar to the bone forming cells in mammals. These mesenchyme cells use calcium from the sea water, which travels to the site where the shell starts to form. About half of the carbonate comes from carbon dioxide that the animals make as they breathe, but it is not known how the other half gets to the site of biomineralization.

Producing a skeleton generates acid, and marine animals need to be able to regulate their pH levels, as too acidic environments can dissolve the calcium carbonate and threatening to destroy the developing shell. How cells accumulate enough carbonate to make their shells, and how they cope with acidity is still poorly understood.

Here, Hu et al. address this problem by studying purple sea urchin larvae, revealing that they use ion transporters to gather bicarbonate from seawater. These structures are part of a group of bicarbonate transporters known as the ‘SLC4 transporter family’, which sit across the membrane of the mesenchyme cells and move the bicarbonate ions along. As the sea urchin larvae develop, the levels of the transporter protein start to rise in mesenchyme cells, peaking around the time they are producing the skeleton.

Stopping the production of the transporter hindered the larvae from building normal skeletons and also made their cells more acidic. It turns out that bicarbonate is more than a skeleton ingredient – it also helps to buffer the acid made in the process. Bicarbonate ions can combine with acidic molecules to form water and carbon dioxide. Bicarbonate pumped in from the sea neutralises the acidic molecules made during calcium carbonate formation, which helps to stabilize pH levels.

When the acidity of the water was experimentally increased, it prompted the sea urchins to produce more of the SLC4 transporters, revealing that they may have another role to play. Their acid-neutralizing capability helped the animals to cope with changes in their environment. Taking on more bicarbonate could therefore help to compensate for rising acidity, allowing skeleton production to carry on as normal.

This last finding is important in the context of ocean acidification. As the amount of carbon dioxide in the atmosphere increases, more of the gas dissolves in the sea. The chemical reactions that follow make the water more acidic and decreases the pH levels of the sea. Understanding how animals make their skeletons and shells, and manage acid, could reveal how they will cope as the environment changes in the future.

Physiological controls of large-scale patterning in planarian regeneration: a molecular and computational perspective on growth and form

Planaria are complex metazoans that repair damage to their bodies and cease remodeling when a correct anatomy has been achieved. This model system offers a unique opportunity to understand how large-scale anatomical homeostasis emerges from the activities of individual cells. Much progress has been made on the molecular genetics of stem cell activity in planaria. However, recent data also indicate that the global pattern is regulated by physiological circuits composed of ionic and neurotransmitter signaling. Here, we overview the multi-scale problem of understanding pattern regulation in planaria, with specific focus on bioelectric signaling via ion channels and gap junctions (electrical synapses), and computational efforts to extract explanatory models from functional and molecular data on regeneration. We present a perspective that interprets results in this fascinating field using concepts from dynamical systems theory and computational neuroscience. Serving as a tractable nexus between genetic, physiological, and computational approaches to pattern regulation, planarian pattern homeostasis harbors many deep insights for regenerative medicine, evolutionary biology, and engineering.