Visualization of Ca²+ signaling during embryonic skeletal muscle formation in vertebrates

The critical role of cardiolipin in metazoan differentiation, development, and maturation

Cardiolipins are phospholipids that are central to proper mitochondrial functioning. Because mitochondria play crucial roles in differentiation, development, and maturation, we would also expect cardiolipin to play major roles in these processes. Indeed, cardiolipin has been implicated in the mechanism of three human diseases that affect young infants, implying developmental abnormalities. In this review, we will: (1) Review the biology of cardiolipin; (2) Outline the evidence for essential roles of cardiolipin during organismal development, including embryogenesis and cell maturation in vertebrate organisms; (3) Place the role(s) of cardiolipin during embryogenesis within the larger context of the roles of mitochondria in development; and (4) Suggest avenues for future research.

Post-gastrulation transition from whole-body to tissue-specific intercellular calcium signaling in the appendicularian tunicate Oikopleuradioica

We recently described calcium signaling in the appendicularian tunicate Oikopleura dioica during pre-gastrulation stages, and showed that regularly occurring calcium waves progress throughout the embryo in a characteristic spatiotemporal pattern from an initiation site in muscle lineage blastomeres (Mikhaleva et al., 2019). Here, we have extended our observations to the period spanning from gastrulation to post-hatching stages. We find that repetitive Ca2+ waves persist throughout this developmental window, albeit with a gradual increase in frequency. The initiation site of the waves shifts from muscle cells at gastrulation and early tailbud stages, to the central nervous system at late tailbud and post-hatching stages, indicating a transition from muscle-driven to neurally driven events as tail movements emerge. At these later stages, both the voltage gated Na + channel blocker tetrodotoxin (TTX) and the T-type Ca2+ channel blocker and nAChR antagonist mecamylamine eliminate tail movements. At late post-hatching stages, mecamylamine blocks Ca2+ signals in the muscles but not the central nervous system. Post-gastrulation Ca2+ signals also arise in epithelial cells, first in a haphazard pattern in scattered cells during tailbud stages, evolving after hatching into repetitive rostrocaudal waves with a different frequency than the nervous system-to-muscle waves, and insensitive to mecamylamine. The desynchronization of Ca2+ waves arising in different parts of the body indicates a shift from whole-body to tissue/organ-specific Ca2+ signaling dynamics as organogenesis occurs, with neurally driven Ca2+ signaling dominating at the later stages when behavior emerges.

Zebrafish as a Model for the Study of Lipid-Lowering Drug-Induced Myopathies

Drug-induced myopathies are classified as acquired myopathies caused by exogenous factors. These pathological conditions develop in patients without muscle disease and are triggered by a variety of medicaments, including lipid-lowering drugs (LLDs) such as statins, fibrates, and ezetimibe. Here we summarise the current knowledge gained via studies conducted using various models, such as cell lines and mammalian models, and compare them with the results obtained in zebrafish (Danio rerio) studies. Zebrafish have proven to be an excellent research tool for studying dyslipidaemias as a model of these pathological conditions. This system enables in-vivo characterization of drug and gene candidates to further the understanding of disease aetiology and develop new therapeutic strategies. Our review also considers important environmental issues arising from the indiscriminate use of LLDs worldwide. The widespread use and importance of drugs such as statins and fibrates justify the need for the meticulous study of their mechanism of action and the side effects they cause.

Role of Two-Pore Channels in Embryonic Development and Cellular Differentiation

Since the identification of nicotinic acid adenine dinucleotide phosphate (NAADP) and its putative target, the two-pore channel (TPC), the NAADP/TPC/Ca2+ signaling pathway has been reported to play a role in a diverse range of functions in a variety of different cell types. TPCs have also been associated with a number of diseases, which arise when their activity is perturbed. In addition, TPCs have been shown to play key roles in various embryological processes and during the differentiation of a variety of cell types. Here, we review the role of NAADP/TPC/Ca2+ signaling during early embryonic development and cellular differentiation. We pay particular attention to the role of TPC2 in the development and maturation of early neuromuscular activity in zebrafish, and during the differentiation of isolated osteoclasts, endothelial cells, and keratinocytes. Our aim is to emphasize the conserved features of TPC-mediated Ca2+ signaling in a number of selected examples.

Nifedipine toxicity is exacerbated by acetyl l-carnitine but alleviated by low-dose ketamine in zebrafish in vivo

Calcium channel blocker (CCB) poisoning is a common and sometimes life-threatening emergency. Our previous studies have shown that acetyl l-carnitine (ALCAR) prevents cardiotoxicity and developmental toxicity induced by verapamil, a CCB used to treat patients with hypertension. Here, we tested whether toxicities of nifedipine, a dihydropyridine CCB used to treat hypertension, can also be mitigated by co-treatment with ALCAR. In the zebrafish embryos at three different developmental stages, nifedipine induced developmental toxicity with pericardial sac edema in a dose-dependent manner, which were surprisingly exacerbated with ALCAR co-treatment. Even with low-dose nifedipine (5 μm), when the pericardial sac looked normal, ALCAR co-treatment showed pericardial sac edema. We hypothesized that toxicity by nifedipine, a vasodilator, may be prevented by ketamine, a known vasoconstrictor. Nifedipine toxicity in the embryos was effectively prevented by co-treatment with low (subanesthetic) doses (25-100 μm added to the water) of ketamine, although a high dose of ketamine (2 mm added to the water) partially prevented the toxicity.As expected of a CCB, nifedipine either in the presence or absence of ketamine-reduced metabolic reactive oxygen species (ROS), a downstream product of calcium signaling, in the rapidly developing digestive system. However, nifedipine induced ROS in the trunk region that showed significantly stunted growth indicating that the tissues under stress potentially produced pathologic ROS. To the best of our knowledge, these studies for the first time show that nifedipine and the dietary supplement ALCAR together induce adverse effects while providing evidence on the therapeutic efficacy of subanesthetic doses of ketamine against nifedipine toxicity in vivo.

Characterization of calcium transients during early embryogenesis in ascidians Ciona robusta (Ciona intestinalis type A) and Ciona savignyi

The calcium ion (Ca²⁺) is an important second messenger, and a rapid increase in Ca²⁺ level (Ca²⁺ transient) is involved in various aspects of embryogenesis. Although Ca²⁺ transients play an important role in early developmental stages, little is known about their dynamics throughout embryogenesis. Here, Ca²⁺ transients were characterized by visualizing Ca²⁺ dynamics in developing chordate embryos using a fluorescent protein-based Ca²⁺ indicator, GCaMP6s in combination with finely tuned microscopy. Ca²⁺ transients were detected in precursors of muscle cells in the late gastrula stage. In the neurula stage, repetitive Ca²⁺ transients were observed in left and right neurogenic cells, including visceral ganglion (VG) precursors, and the duration of Ca²⁺ transients was 39±4s. In the early tailbud stage, Ca²⁺ transients were observed in differentiating precursors of nerve cord neurons. A small population of VG precursors showed rhythmical Ca²⁺ transients with a duration of 22±4s, suggesting a central pattern generator (CPG) origin. At the mid tailbud stage, Ca²⁺transients were observed in a wide area of epidermal cells and named CTECs. The number and frequency of CTECs increased drastically in late tailbud stages, and the timing of the increase coincided with that of the relaxation of the tail bending. The experiment using Ca²⁺ chelator showed that the CTECs were largely depending on the extracellular Ca²⁺. The waveform analysis of Ca²⁺ transients revealed different features according to duration and frequency. The comprehensive characterization of Ca²⁺ transients during early ascidian embryogenesis will help our understanding of the role of Ca²⁺ signaling in chordate embryogenesis.

Ca2+ release via two-pore channel type 2 (TPC2) is required for slow muscle cell myofibrillogenesis and myotomal patterning in intact zebrafish embryos

We recently demonstrated a critical role for two-pore channel type 2 (TPC2)-mediated Ca²⁺ release during the differentiation of slow (skeletal) muscle cells (SMC) in intact zebrafish embryos, via the introduction of a translational-blocking morpholino antisense oligonucleotide (MO). Here, we extend our study and demonstrate that knockdown of TPC2 with a non-overlapping splice-blocking MO, knockout of TPC2 (via the generation of a tpcn2^dhkz1a mutant line of zebrafish using CRISPR/Cas9 gene-editing), or the pharmacological inhibition of TPC2 action with bafilomycin A1 or trans-ned-19, also lead to a significant attenuation of SMC differentiation, characterized by a disruption of SMC myofibrillogenesis and gross morphological changes in the trunk musculature. When the morphants were injected with tpcn2-mRNA or were treated with IP₃/BM or caffeine (agonists of the inositol 1,4,5-trisphosphate receptor (IP₃R) and ryanodine receptor (RyR), respectively), many aspects of myofibrillogenesis and myotomal patterning (and in the case of the pharmacological treatments, the Ca²⁺ signals generated in the SMCs), were rescued. STED super-resolution microscopy revealed a close physical relationship between clusters of RyR in the terminal cisternae of the sarcoplasmic reticulum (SR), and TPC2 in lysosomes, with a mean estimated separation of ~52-87nm. Our data therefore add to the increasing body of evidence, which indicate that localized Ca²⁺ release via TPC2 might trigger the generation of more global Ca²⁺ release from the SR via Ca²⁺-induced Ca²⁺ release.

Ca2+ dynamics in zebrafish morphogenesis

Intracellular calcium ion (Ca²⁺) signaling is heavily involved in development, as illustrated by the use of a number of Ca²⁺ indicators. However, continuous Ca²⁺ patterns during morphogenesis have not yet been studied using fluorescence resonance energy transfer to track the Ca²⁺ sensor. In the present study, we monitored Ca²⁺ levels during zebrafish morphogenesis and differentiation with yellow cameleon, YC2.12. Our results show not only clear changes in Ca²⁺ levels but also continuous Ca²⁺ patterns at 24 hpf and later periods for the first time. Serial Ca²⁺dynamics during early pharyngula period (Prim-5-20; 24–33 hpf) was successfully observed with cameleon, which have not reported anywhere yet. In fact, high Ca²⁺ level occurred concurrently with hindbrain development in segmentation and pharyngula periods. Ca²⁺ patterns in the late gastrula through segmentation periods which were obtained with cameleon, were similar to those obtained previously with other Ca²⁺sensor. Our results suggested that the use of various Ca²⁺ sensors may lead to novel findings in studies of Ca²⁺ dynamics. We hope that these results will prove valuable for further research in Ca²⁺ signaling.

Spontaneous long-range calcium waves in developing butterfly wings

Background

Butterfly wing color patterns emerge as the result of a regular arrangement of scales produced by epithelial scale cells at the pupal stage. These color patterns and scale arrangements are coordinated throughout the wing. However, the mechanism by which the development of scale cells is controlled across the entire wing remains elusive. In the present study, we used pupal wings of the blue pansy butterfly, Junonia orithya, which has distinct eyespots, to examine the possible involvement of Ca²⁺ waves in wing development.

Results

Here, we demonstrate that the developing pupal wing tissue of the blue pansy butterfly displayed spontaneous low-frequency Ca²⁺ waves in vivo that propagated slowly over long distances. Some waves appeared to be released from the immediate peripheries of the prospective eyespot and discal spot, though it was often difficult to identify the specific origins of these waves. Physical damage, which is known to induce ectopic eyespots, led to the radiation of Ca²⁺ waves from the immediate periphery of the damaged site. Thapsigargin, which is a specific inhibitor of Ca²⁺-ATPases in the endoplasmic reticulum, induced an acute increase in cytoplasmic Ca²⁺ levels and halted the spontaneous Ca²⁺ waves. Additionally, thapsigargin-treated wings showed incomplete scale development as well as other scale and color pattern abnormalities.

Conclusions

We identified a novel form of Ca²⁺ waves, spontaneous low-frequency slow waves, which travel over exceptionally long distances. Our results suggest that spontaneous Ca²⁺ waves play a critical role in the coordinated development of scale arrangements and possibly in color pattern formation in butterflies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0067-8) contains supplementary material, which is available to authorized users.

Three calcium-sensitive genes, fus, brd3 and wdr5, are highly expressed in neural and renal territories during amphibian development

Numerous Ca(2+) signaling events have been associated with early development of vertebrate embryo, from fertilization to organogenesis. In Xenopus laevis, Ca(2+) signals are key regulators in the earliest steps of the nervous system development. If neural determination is one of the best-characterized examples of the role of Ca(2+) during embryogenesis, increasing literature supports a determining role of organogenesis and differentiation. In blastula the cells of the presumptive ectoderm (animal caps) are pluripotent and can be induced toward neural fate with an intracellular increase of free Ca(2+) triggered by caffeine. To identify genes that are transcribed early upon Ca(2+) stimuli and involved in neural determination, we have constructed a subtractive cDNA library between neuralized and non-neuralized animal caps. Here we present the expression pattern of three new Ca(2+)-sensitive genes: fus (fused in sarcoma), brd3 (bromodomain containing 3) and wdr5 (WD repeat domain 5) as they all represent potential regulators of the transcriptional machinery. Using in situ hybridization we illustrated the spatial expression pattern of fus, brd3 and wdr5 during early developmental stages of Xenopus embryos. Strikingly, their domains of expression are not restricted to neural territories. They all share a specific expression throughout renal organogenesis which has been found to rely also on Ca(2+) signaling. This therefore highlights the key function of Ca(2+) target genes in specific territories during early development. We propose that Ca(2+) signaling through modulation of fus, brd3 and wdr5 expressions can control the transcription machinery to achieve proper embryogenesis. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.