A magnetic protein biocompass

Functional Immobilization of a Biofilm-Releasing Glycoside Hydrolase Dispersin B on Magnetic Nanoparticles

Dispersin B (DspB) is a member of glycoside hydrolase family 20 (GH20) and catalyzes degradation of biofilms forming by pathogenic bacteria such as Staphylococcus aureus. Magnetoreceptor (MagR) is a magnetic protein that can be used as a fusion partner for functionally immobilizing proteins on magnetic surfaces. In the present study, a recombinant protein DspB-MagR was constructed by fusing MagR to the C-terminus of DspB and expressed in Escherichia coli. Magnetic immobilization of purified DspB-MagR on magnetic core-shell structured Fe3O4@SiO2 nanoparticles was achieved and characterized by means of various techniques including SDS-PAGE, Fourier transform infrared spectroscopy, thermogravimetric analysis, zeta potential measurement, and scanning electron microscopy. It was evaluated the influence of temperature, pH, and storage time on the performance of immobilized DspB-MagR on Fe3O4@SiO2 nanoparticles. Removal of biofilms forming by Staphylococcus aureus and other medical sourced bacterial species was achieved by using Fe3O4@SiO2 nanoparticles loading with DspB-MagR. This work promoted potential applications of DspB and similar enzymes for medical purposes.

Tag-mediated single-step purification and immobilization of recombinant proteins toward protein-engineered advanced materials

Background

The potential applications of protein-engineered functional materials are so wide and exciting that the interest in these eco-friendly advanced materials will further expand in the future. Tag-mediated protein purification/immobilization technologies have emerged as green and cost-effective approaches for the fabrication of such materials. Strategies that combine the purification and immobilization of recombinant proteins/peptides onto/into natural, synthetic or hybrid materials in a single-step are arising and attracting increasing interest.

Aim of Review

This review highlights the most significant advances of the last 5 years within the scope of tag-mediated protein purification/immobilization and elucidates their contributions for the development of efficient single-step purification and immobilization strategies. Recent progresses in the field of protein-engineered materials created using innovative protein-tag combinations and future opportunities created by these new technologies are also summarized and identified herein.

Key Scientific Concepts of Review

Protein purification/immobilization tags present a remarkable ability to establish specific non-covalent/covalent interactions between solid materials and biological elements, which prompted the creation of tailor-made and advanced functional materials, and of next-generation hybrid materials. Affinity tags can bind to a wide range of materials (of synthetic, natural or hybrid nature), being most suitable for protein purification. Covalently binding tags are most suitable for long-term protein immobilization, but can only bind naturally to protein-based materials. Hybrid affinity-covalently binding tags have allowed efficient one-step purification and immobilization of proteins onto different materials, as well as the development of innovative protein-engineered materials. Self-aggregating tags have been particularly useful in combination with other tags for generating protein-engineered materials with self-assembling, flexible and/or responsive properties. While these tags have been mainly explored for independent protein purification, immobilization or functionalization purposes, efficient strategies that combine tag-mediated purification and immobilization/functionalization in a single-step will be essential to guarantee the sustainable manufacturing of advanced protein-engineered materials.

"Magnetism-Optogenetic" System for Wireless and Highly Sensitive Neuromodulation

Neuromodulation is becoming more and more important in studying brain function, disease treatment, and brain-computer interfaces. However, traditional regulation methods cannot effectively achieve both wireless regulation and highly sensitive response, which are essential factors in neuromodulation. In this paper, a "magnetism-optogenetic" system is constructed, which uses a magnetic field to drive mechanoluminescent materials (ZnS:Cu) to generate light, thus stimulating photogenetic proteins. This system effectively combines the wireless magnetic regulation with the high sensitivity of optogenetics. The results show that the luminous intensity of this system changes with the power of an external magnetic field. In addition, under the continuous stimulation of the wireless magnetic field, this system can activate hippocampal-related neural responses and induce the expression of C-fos. In the end, this system can further regulate the movement behavior of rats with C1V1 protein expression in the primary motor cortex. This new magnetism-optogenetic system will provide an excellent reference for wireless and highly sensitive neuromodulation.

Effect of weak alternating magnetic fields on planarian regeneration

We investigated the effect of weak combined magnetic field (CMF) on stem cell proliferation and regeneration of the planarian Schmidtea mediterranea. CMF parameters were set in accordance with Valery Lednev's theory of magnetic parametric resonance. It was shown that CMF with an amplitude of 74 μT and a frequency of 30 Hz accelerated the growth of the planarian head blastema by 25%. Alterations of the frequency in range from 27 to 33 Hz led to a complete disappearance of the effect. A further decrease in the CMF frequency inhibited regeneration. The maximum inhibition (24%) was observed at a frequency of 16 Hz. A further decrease in the CMF frequency (down to 13 Hz) led to disappearance of the described effect. Regeneration rate changes under the CMF are influenced by alterations in stem cell mitotic activity, which in turn depends on the wound-induced gene expression level. Thus, the CMF, preset in accordance to the Lednev's theory, can specifically influence the expression of regeneration-related genes and regeneration itself, what can find biomedical applications.

Molecular Diagnostic System Using Engineered Fusion Protein-Conjugated Magnetic Nanoparticles

To effectively control the spread of new infectious diseases, there is a need for highly sensitive diagnostic methods to detect viral nucleic acids rapidly. This study outlines a universal and simple detection strategy that uses magnetic nanoparticles (MNPs) and a novel MagR-MazE fusion protein for molecular diagnostics to facilitate sensitive detection. This study has engineered a novel MNP conjugate that can be generated easily, without using many chemical reagents. The technique is a nucleic acid detection method, using MagR-MazE fusion protein-conjugated MNPs, where the results can be visualized with the naked eye, regardless of the oligonucleotide sequences of the target in the lateral flow assay. This method could sensitively detect polymerase chain reaction (PCR) products of 16S ribosomal RNA (rRNA) and the 2019-nCoV-N-positive control gene in 5 min. It shows a low limit of detection (LoD) of 0.013 ng/μL for dsDNA. It is simpler and more rapid, sensitive, and versatile than other techniques, making it suitable for point-of-care testing. The proposed detection system and MNP conjugation strategy using a fusion protein can be widely applied to various fields requiring rapid on-site diagnosis.

Expression of CRY2 Gene in the Brain Is Related to Human Navigation

Navigation is a complex cognitive process. CRY2 gene has been proposed to play an important role in navigation behaviors in various non-human animal species. Utilizing a recently developed neuroimaging-transcriptomics approach, the present study reported a tentative link between the CRY2 gene and human navigation. Specifically, we showed a significant pattern similarity between CRY2 gene expression in the human brain and navigation-related neural activation in functional magnetic resonance imaging. To further illuminate the functionality of CRY2 in human navigation, we examined the correlation between CRY2 expression and various cognitive processes underlying navigation, and found high correlation of CRY2 expression with neural activity of multiple cognitive domains, particularly object and shape perception and spatial memory. Further analyses on the relation between the neural activity of human navigation and the expression maps of genes of two CRY2-related pathways, i.e., the magnetoreceptive and circadian-related functions, found a trend of correlation for the CLOCK gene, a core circadian regulator gene, suggesting that CRY2 may modulate human navigation through its role in circadian rhythm. This observation was further confirmed by a behavioral study where individuals with better circadian regularity in daily life showed better sense of direction. Taken together, our study presents the first neural evidence that links CRY2 with human navigation, possibly through the modulation of circadian rhythm.

Modulation of MagR magnetic properties via iron-sulfur cluster binding

Iron-sulfur clusters are essential cofactors found in all kingdoms of life and play essential roles in fundamental processes, including but not limited to respiration, photosynthesis, and nitrogen fixation. The chemistry of iron-sulfur clusters makes them ideal for sensing various redox environmental signals, while the physics of iron-sulfur clusters and its host proteins have been long overlooked. One such protein, MagR, has been proposed as a putative animal magnetoreceptor. It forms a rod-like complex with cryptochromes (Cry) and possesses intrinsic magnetic moment. However, the magnetism modulation of MagR remains unknown. Here in this study, iron-sulfur cluster binding in MagR has been characterized. Three conserved cysteines of MagR play different roles in iron-sulfur cluster binding. Two forms of iron-sulfur clusters binding have been identified in pigeon MagR and showed different magnetic properties: [3Fe-4S]-MagR appears to be superparamagnetic and has saturation magnetization at 5 K but [2Fe-2S]-MagR is paramagnetic. While at 300 K, [2Fe-2S]-MagR is diamagnetic but [3Fe-4S]-MagR is paramagnetic. Together, the different types of iron-sulfur cluster binding in MagR attribute distinguished magnetic properties, which may provide a fascinating mechanism for animals to modulate the sensitivity in magnetic sensing.

Nanotechnology Enables Novel Modalities for Neuromodulation

Neuromodulation is of great importance both as a fundamental neuroscience research tool for analyzing and understanding the brain function, and as a therapeutic avenue for treating brain disorders. Here, an overview of conceptual and technical progress in developing neuromodulation strategies is provided, and it is suggested that recent advances in nanotechnology are enabling novel neuromodulation modalities with less invasiveness, improved biointerfaces, deeper penetration, and higher spatiotemporal precision. The use of nanotechnology and the employment of versatile nanomaterials and nanoscale devices with tailored physical properties have led to considerable research progress. To conclude, an outlook discussing current challenges and future directions for next-generation neuromodulation modalities is presented.

Removal or component reversal of local geomagnetic field affects foraging orientation preference in migratory insect brown planthopper Nilaparvata lugens

Background

Migratory brown planthopper Nilaparvata lugens (N. lugens) annually migrates to Northeast Asia in spring and returns to Southeast Asia in autumn. However, mechanisms for orientation and navigation during their flight remain largely unknown. The geomagnetic field (GMF) is an important source of directional information for animals (including N. lugens), yet the magnetic compass involved has not been fully identified.

Methods

Here we assessed the influences of GMF on the foraging orientation preference of N. lugens by removing or component reversal of local GMF. At the same time, we examined the role of iron-sulfur cluster assembly1 (IscA1), a putative component of magnetoreceptor, in the foraging orientation preference of N. lugens under the controlled magnetic fields by RNA silencing (RNAi).

Results

We found that the near-zero magnetic field (NZMF) or vertical reversal of GMF could lead to N. lugens losing the foraging orientation preference, suggesting that a normal level of GMF, in the way of either intensity or inclination, was essential for the foraging orientation of N. lugens. Moreover, the gene knockdown of IscA1, also affected the foraging orientation preference of N. lugens, pointing out a potential role of IscA1 in the insects’ sensing of variation in the GMF.

Discussion

These results suggested a foraging orientation preference is associated with the GMF and revealed new insights into the relationship between the IscA1 and magnetosensitivity mechanism in N. lugens.

Stimuli-Responsive Natural Proteins and Their Applications

Natural proteins are essential biomacromolecules that fulfill versatile functions in the living organism, such as their usage as cytoskeleton, nutriment transporter, homeostasis controller, catalyzer, or immune guarder. Due to the excellent mechanical properties and good biocompatibility/biodegradability, natural protein-based biomaterials are well equipped for prospective applications in various fields. Among these natural proteins, stimuli-responsive proteins can be reversibly and precisely manipulated on demand, rendering the protein-based biomaterials promising candidates for numerous applications, including disease detection, drug delivery, bio-sensing, and regenerative medicine. Therefore, we present some typical natural proteins with diverse physical stimuli-responsive properties, including temperature, light, force, electrical, and magnetic sensing in this review. The structure-function mechanism of these proteins is discussed in detail. Finally, we give a summary and perspective for the development of stimuli-responsive proteins.

Revisiting the Potential Functionality of the MagR Protein

Recent findings have sparked great interest in the putative magnetic receptor protein MagR. However, in vivo experiments have revealed no magnetic moment of MagR at room temperature. Nevertheless, the interaction of MagR and MagR fusion proteins with silica-coated magnetite beads have proven useful for protein purification. In this study, we recombinantly produced two different MagR proteins in Escherichia coli BL21(DE3) to (1) expand earlier protein purification studies, (2) test if MagR can magnetize whole E. coli cells once it is expressed to a high cytosolic, soluble titer, and (3) investigate the MagR-expressing E. coli cells’ magnetic properties at low temperatures. Our results show that MagR induces no measurable, permanent magnetic moment in cells at low temperatures, indicating no usability for cell magnetization. Furthermore, we show the limited usability for magnetic bead-based protein purification, thus closing the current knowledge gap between theoretical considerations and empirical data on the MagR protein.

Light-dependent reactions of animal circadian photoreceptor cryptochrome

Circadian rhythms are endogenous autonomous 24-h oscillations that are generated by a transcription-translation feedback loop (TTFL). In the positive arm of the TTFL, two transcription factors activate the expression of two genes of the negative arm as well as circadian clock-regulated genes. The circadian clocks are reset through photoreceptor proteins by sunlight in the early morning to keep synchrony with the geological clock. Among animal circadian photoreceptors, Drosophila Cryptochrome (DmCRY) has some unique properties because Drosophila has a single cryptochrome (CRY) that appears to have functions which are specific to organs or tissues, or even to a subset of cells. In mammals, CRYs are not photoreceptors but function in the TTFL, while insects have a light-insensitive mammalian-like CRY or a Drosophila-like photoreceptor CRY (or both). Here, we postulate that as being just one CRY in Drosophila, DmCRY might play different roles in different tissues/organs in a context-dependent manner. In addition to being a circadian photoreceptor/protein, attributing also a magnetoreception function to DmCRY has increased its workload. Considering that DmCRY senses photons as a photoreceptor but also can regulate many different events in a light-dependent manner, differential protein-protein interactions (PPIs) of DmCRY might play a critical role in the generation of such diverse outputs. Therefore, we need to add novel approaches in addition to the current ones to study multiple and context-dependent functions of DmCRY by adopting recently developed techniques. Successful identification of transient/fast PPIs on a scale of minutes would enhance our understanding of light-dependent and/or magnetoreception-associated reactions.

Effects of an electric field on sleep quality and life span mediated by ultraviolet (UV)-A/blue light photoreceptor CRYPTOCHROME in Drosophila

Although electric fields (EF) exert beneficial effects on animal wound healing, differentiation, cancers and rheumatoid arthritis, the molecular mechanisms of these effects have remained unclear about a half century. Therefore, we aimed to elucidate the molecular mechanisms underlying EF effects in Drosophila melanogaster as a genetic animal model. Here we show that the sleep quality of wild type (WT) flies was improved by exposure to a 50-Hz (35 kV/m) constant electric field during the day time, but not during the night time. The effect was undetectable in cryptochrome mutant (cry^b) flies. Exposure to a 50-Hz electric field under low nutrient conditions elongated the lifespan of male and female WT flies by ~ 18%, but not of several cry mutants and cry RNAi strains. Metabolome analysis indicated that the adenosine triphosphate (ATP) content was higher in intact WT than cry gene mutant strains exposed to an electric field. A putative magnetoreceptor protein and UV-A/blue light photoreceptor, CRYPTOCHROME (CRY) is involved in electric field (EF) receptors in animals. The present findings constitute hitherto unknown genetic evidence of a CRY-based system that is electric field sensitive in animals.

In addition to cryptochrome 2, magnetic particles with olfactory co-receptor are important for magnetic orientation in termites

The volatile trail pheromone is an ephemeral chemical cue, whereas the geomagnetic field (GMF) provides a stable positional reference. However, it is unclear whether and how the cryptic termites perceive the GMF for orientation in light or darkness until now. Here, we found that the two termite species, Reticulitermes chinensis and Odontotermes formosanus, use the GMF for orientation. Our silencing cryptochrome 2 (Cry2) impaired magnetic orientation in white light but had no significant impact in complete darkness, suggesting that Cry2 can mediate magnetic orientation in termites only under light. Coincidentally, the presence of magnetic particles enabled the magnetic orientation of termites in darkness. When knock-downing the olfactory co-receptor (Orco) to exclude the effect of trail pheromone, unexpectedly, we found that the Orco participated in termite magnetic orientation under both light and darkness. Our findings revealed a novel magnetoreception model depending on the joint action of radical pair, magnetic particle, and olfactory co-receptor.

Gao et al. analyze the role of magnetoreceptor candidates cryptochrome 2 (Cry2), magnetic particles and olfactory coreceptor (Orco) in magnetic orientation in two termite species. They report that termites use Cry2 for directional preference in white light, magnetic particles in darkness, and Orco participates in termite magnetic orientation under both light and darkness.

Bioinspired Magnetic Nanochains for Medicine

Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely used for medicine, both in therapy and diagnosis. Their guided assembly into anisotropic structures, such as nanochains, has recently opened new research avenues; for instance, targeted drug delivery. Interestingly, magnetic nanochains do occur in nature, and they are thought to be involved in the navigation and geographic orientation of a variety of animals and bacteria, although many open questions on their formation and functioning remain. In this review, we will analyze what is known about the natural formation of magnetic nanochains, as well as the synthetic protocols to produce them in the laboratory, to conclude with an overview of medical applications and an outlook on future opportunities in this exciting research field.

Toward Quantitative Bio-sensing with Nitrogen-Vacancy Center in Diamond

The long-dreamed-of capability of monitoring the molecular machinery in living systems has not been realized yet, mainly due to the technical limitations of current sensing technologies. However, recently emerging quantum sensors are showing great promise for molecular detection and imaging. One of such sensing qubits is the nitrogen-vacancy (NV) center, a photoluminescent impurity in a diamond lattice with unique room-temperature optical and spin properties. This atomic-sized quantum emitter has the ability to quantitatively measure nanoscale electromagnetic fields via optical means at ambient conditions. Moreover, the unlimited photostability of NV centers, combined with the excellent diamond biocompatibility and the possibility of diamond nanoparticles internalization into the living cells, makes NV-based sensors one of the most promising and versatile platforms for various life-science applications. In this review, we will summarize the latest developments of NV-based quantum sensing with a focus on biomedical applications, including measurements of magnetic biomaterials, intracellular temperature, localized physiological species, action potentials, and electronic and nuclear spins. We will also outline the main unresolved challenges and provide future perspectives of many promising aspects of NV-based bio-sensing.

Transcriptomic analysis reveals the inhibition of reproduction in rice brown planthopper, Nilaparvata lugens, after silencing the gene of MagR (IscA1)

MagR (IscA1) is a member of the iron-sulphur cluster assembly proteins, which plays vital roles in many physiological processes, such as energy metabolism, electron transfer, iron homeostasis, heme biosynthesis and physiologically magnetic response. Its deletion leads to the loss of mitochondrial DNA, inactivation of iron-sulphur proteins and abnormal embryonic development in organisms. However, the physiological roles of MagR in insects are unclear. This study characterized the effects and molecular regulatory mechanism of MagR gene silencing on the reproduction of brachypterous female adults of Nilaparvata lugens. After silencing the MagR gene using RNAi approach, the duration of reproductive period was shortened and the fecundity and hatchability reduced significantly. A total of 479 differentially expressed genes (DEGs) were identified for female adults after 2 days of dsRNA injection through RNA-sequencing technology, including 352 significantly upregulated DEGs and 127 significantly downregulated DEGs, among which 44 DEGs were considered the key genes involved in the effects of NlMagR silencing on the reproduction, revealing the regulatory mechanism of MagR at RNA transcription level and providing a new strategy for the control of N. lugens.

Magnetic sensitivity of cryptochrome 4 from a migratory songbird

Night-migratory songbirds are remarkably proficient navigators¹. Flying alone and often over great distances, they use various directional cues including, crucially, a light-dependent magnetic compass^2,3. The mechanism of this compass has been suggested to rely on the quantum spin dynamics of photoinduced radical pairs in cryptochrome flavoproteins located in the retinas of the birds^4-7. Here we show that the photochemistry of cryptochrome 4 (CRY4) from the night-migratory European robin (Erithacus rubecula) is magnetically sensitive in vitro, and more so than CRY4 from two non-migratory bird species, chicken (Gallus gallus) and pigeon (Columba livia). Site-specific mutations of ErCRY4 reveal the roles of four successive flavin-tryptophan radical pairs in generating magnetic field effects and in stabilizing potential signalling states in a way that could enable sensing and signalling functions to be independently optimized in night-migratory birds.

Comparison of ELF-EMFs stimulation with current stimulation on the regulation of LTP of SC-CA1 synapses in young rat hippocampus

BACKGROUND

Long-term potentiation (LTP) is an important functional indicator for synaptic plasticity. Extremely low frequency electromagnetic fields (ELF-EMFs) are a physical means to regulate LTP, which induce induced currents. It is unknown whether induced current is the key factor when LTP is regulated by ELF-EMFs.New Method: A method is proposed for calculating the current value induced by ELF-EMFs. Then, a comparison of ELF-EMFs with current on the regulation of theta-burst or high-frequency stimulation (TBS/HFS)-LTP was performed.

RESULTS

The LTP after ELF-EMFs and μA current regulation was significantly reduced. The regulatory effect of 0.1 μA current on LTP was similar with 100 Hz/2 mT ELF-EMFs, while 0.2 μA had a stronger regulatory effect than 200 Hz/2 mT on HFS-LTP.Comparison with Existing Methods: Most of the existing methods were used to calculate the induced current in human models, while we present a more accurate model for calculating the induced current induced by ELF-EMFs in the rat brain slices.

CONCLUSIONS

This work indicated that μA current and ELF-EMFs stimulation reduced LTP. Also, we demonstrated that the regulatory effect of ELF-EMFs on LTP is not entirely deriving from the induced current, since its magnetic mechanism might have played a certain role.

Cryptochromes: Photochemical and structural insight into magnetoreception

Cryptochromes (CRYs) function as blue light photoreceptors in diverse physiological processes in nearly all kingdoms of life. Over the past several decades, they have emerged as the most likely candidates for light-dependent magnetoreception in animals, however, a long history of conflicts between in vitro photochemistry and in vivo behavioral data complicate validation of CRYs as a magnetosensor. In this review, we highlight the origins of conflicts regarding CRY photochemistry and signal transduction, and identify recent data that provides clarity on potential mechanisms of signal transduction in magnetoreception. The review primarily focuses on examining differences in photochemistry and signal transduction in plant and animal CRYs, and identifies potential modes of convergent evolution within these independent lineages that may identify conserved signaling pathways.

Biological Effects of Space Hypomagnetic Environment on Circadian Rhythm

The intrinsic earth magnetic field (geomagnetic field, GMF) provides an essential environmental condition for most living organisms to adapt the solar cycle by rhythmically synchronizing physiological and behavioral processes. However, hypomagnetic field (HMF) of outer space, the Moon, and the Mars differs much from GMF, which poses a critical problem to astronauts during long-term interplanetary missions. Multiple experimental works have been devoted to the HMF effects on circadian rhythm and found that HMF perturbs circadian rhythms and profoundly contributes to health problems such as sleep disorders, altered metabolic as well as neurological diseases. By systemizing the latest progress on interdisciplinary cooperation between magnetobiology and chronobiology, this review sheds light on the health effects of HMF on circadian rhythms by elaborating the underlying circadian clock machinery and molecular processes.

Mutational analysis of MpPhy reveals magnetoreception and photosensitivity involvement in secondary metabolites biosynthesis in Monascus purpureus

Light or low frequency magnetic field (LF-MF) as one of the cultivation environments affects secondary metabolites (SMs) production of M. purpureus. Phytochrome (Phy) is a hybrid histidine kinase possessing dual properties of photoreceptor and kinase to sense red and far-red light. The interaction effects of LF-MF and light on SMs of M. purpureus was investigated by knocking out the Phy-like gene in M. purpureus (MpPhy) by homologous recombination. A MpPhy-deletion (ΔMpPhy) strain produced less Monascus pigments (MPs) and monacolin K (mon K) than the wild-type (WT) strain and reduced citrinin production by 78.3% on 10th day but didn't affect the biomass. These results indicated that the MpPhy gene is involved in SMs biosynthesis of M. purpureus. MPs production in WT was decreased significantly when the inoculum was exposed to white/blue/green/red light (500 Lux). But it in ΔMpPhy was no significant difference when exposed to white/red light. The colony size of ΔMpPhy was smaller on potato dextrose agar media containing 0.01% SDS. These results indicated that the deletion of MpPhy gene affected the aerial hyphae and increased sensitivity to cell membrane stress but decreased sensitivity to red light. The inoculum of both WT and ΔMpPhy was exposure to the LF-MF (50 Hz). The accumulation of WT secondary metabolites was not changed, while SMs production of ΔMpPhy was significantly enhanced under exposed to 2.0 mT LF-MF. This indicated that the decrease of SMs caused by the deletion of MpPhy gene was restored by LF-MF. It revealed that there is a crosstalk between magnetoreception and photosensitivity.

A comparative analysis of cone photoreceptor morphology in bowhead and beluga whales

The cetacean visual system is a product of selection pressures favoring underwater vision, yet relatively little is known about it across taxa. Previous studies report several mutations in the opsin genetic sequence in cetaceans, suggesting the evolutionary complete or partial loss of retinal cone photoreceptor function in mysticete and odontocete lineages, respectively. Despite this, limited anatomical evidence suggests cone structures are partially maintained but with absent outer and inner segments in the bowhead retina. The functional consequence and anatomical distributions associated with these unique cone morphologies remain unclear. The current study further investigates the morphology and distribution of cone photoreceptors in the bowhead whale and beluga retina and evaluates the potential functional capacity of these cells' alternative to photoreception. Refined histological and advanced microscopic techniques revealed two additional cone morphologies in the bowhead and beluga retina that have not been previously described. Two proteins involved in magnetosensation were present in these cone structures suggesting the possibility for an alternative functional role in responding to changes in geomagnetic fields. These findings highlight a revised understanding of the unique evolution of cone and gross retinal anatomy in cetaceans, and provide prefatory evidence of potential functional reassignment of these cells.

Application of Inorganic Nanocomposite Hydrogels in Bone Tissue Engineering

Bone defects caused by trauma and surgery are common clinical problems encountered by orthopedic surgeons. Thus, a hard-textured, natural-like biomaterial that enables encapsulated cells to obtain the much-needed biophysical stimulation and produce functional bone tissue is needed. Incorporating nanomaterials into cell-laden hydrogels is a straightforward tactic for producing tissue engineering structures that integrate perfectly with the body and for tailoring the material characteristics of hydrogels without hindering nutrient exchange with the surroundings. In this review, recent developments in inorganic nanocomposite hydrogels for bone tissue engineering that are of vital importance but have not yet been comprehensively reviewed are summarized.

Innate Immune Regulation Under Magnetic Fields With Possible Mechanisms and Therapeutic Applications

With the wide applications of magnetic fields (MFs) in medicine, researchers from different disciplines have gained interest in understanding the effect of various types of MFs on living cells and organisms. In this paper, we mainly focus on the immunological and physical aspects of the immune responses and their mechanisms under different types of MFs. Immune cells were slightly affected by low-frequency alternating MFs but were strongly influenced by moderate-intensity MFs and high-gradient MFs (HGMFs). Larger immune cells, such as macrophages, were more sensitive to HGMFs, which biased the cell polarization into the anti-inflammatory M2 phenotype. Subject to the gradient forces of varying directions and strength, the elongated M2 macrophage also remodeled the cytoskeleton with actin polymerization and changed the membrane receptors and ion channel gating. These alterations were very similar to changes caused by the small GTPase RhoA interference in macrophage. Regulation of iron metabolism may also contribute to the MF effects in macrophages. High MFs were found to regulate the iron content in monocyte-/macrophage-derived osteoclasts by affecting the expression of iron-regulation genes. On the other hand, paramagnetic nanoparticles (NPs) combined with external MFs play an important role in T-cell immunity. Paramagnetic NP-coated T-cells can cluster their T-cell receptors (TCRs) by using an external MF, thus increasing the cell–cell contact and communication followed by enhanced tumor killing capacity. The external MF can also guide the adoptively transferred magnetic NP-coated T-cells to their target sites in vivo, thus dramatically increasing the efficiency of cell therapy. Additionally, iron oxide NPs for ferroptosis-based cancer therapy and other MF-related therapeutic applications with obstacles were also addressed. Furthermore, for a profound understanding of the effect of MFs on immune cells, multidisciplinary research involving both experimental research and theoretical modeling is essential.

Moderate SMFs attenuate bone loss in mice by promoting directional osteogenic differentiation of BMSCs

Background

Osteoporosis is a common metabolic bone disease without effective treatment. Bone marrow-derived mesenchymal stem cells (BMSCs) have the potential to differentiate into multiple cell types. Increased adipogenic differentiation or reduced osteogenic differentiation of BMSCs might lead to osteoporosis. Whether static magnetic fields (SMFs) might influence the adipo-osteogenic differentiation balance of BMSCs remains unknown.

Methods

The effects of SMFs on lineage differentiation of BMSCs and development of osteoporosis were determined by various biochemical (RT-PCR and Western blot), morphological (staining and optical microscopy), and micro-CT assays. Bioinformatics analysis was also used to explore the signaling pathways.

Results

In this study, we found that SMFs (0.2–0.6 T) inhibited the adipogenic differentiation of BMSCs but promoted their osteoblastic differentiation in an intensity-dependent manner. Whole genomic RNA-seq and bioinformatics analysis revealed that SMF (0.6 T) decreased the PPARγ-mediated gene expression but increased the RUNX2-mediated gene transcription in BMSCs. Moreover, SMFs markedly alleviated bone mass loss induced by either dexamethasone or all-trans retinoic acid in mice.

Conclusions

Taken together, our results suggested that SMF-based magnetotherapy might serve as an adjunctive therapeutic option for patients with osteoporosis.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s13287-020-02004-y.

Intrinsically Magnetic Cells: A Review on Their Natural Occurrence and Synthetic Generation

The magnetization of non-magnetic cells has great potential to aid various processes in medicine, but also in bioprocess engineering. Current approaches to magnetize cells with magnetic nanoparticles (MNPs) require cellular uptake or adsorption through in vitro manipulation of cells. A relatively new field of research is "magnetogenetics" which focuses on in vivo production and accumulation of magnetic material. Natural intrinsically magnetic cells (IMCs) produce intracellular, MNPs, and are called magnetotactic bacteria (MTB). In recent years, researchers have unraveled function and structure of numerous proteins from MTB. Furthermore, protein engineering studies on such MTB proteins and other potentially magnetic proteins, like ferritins, highlight that in vivo magnetization of non-magnetic hosts is a thriving field of research. This review summarizes current knowledge on recombinant IMC generation and highlights future steps that can be taken to succeed in transforming non-magnetic cells to IMCs.

A novel isoform of cryptochrome 4 (Cry4b) is expressed in the retina of a night-migratory songbird

The primary sensory molecule underlying light-dependent magnetic compass orientation in migratory birds has still not been identified. The cryptochromes are the only known class of vertebrate proteins which could mediate this mechanism in the avian retina. Cryptochrome 4 of the night-migratory songbird the European robin (Erithacus rubecula; erCry4) has several of the properties needed to be the primary magnetoreceptor in the avian eye. Here, we report on the identification of a novel isoform of erCry4, which we named erCry4b. Cry4b includes an additional exon of 29 amino acids compared to the previously described form of Cry4, now called Cry4a. When comparing the retinal circadian mRNA expression pattern of the already known isoform erCry4a and the novel erCry4b isoform, we find that erCry4a is stably expressed throughout day and night, whereas erCry4b shows a diurnal mRNA oscillation. The differential characteristics of the two erCry4 isoforms regarding their 24-h rhythmicity in mRNA expression leads us to suggest that they might have different functions. Based on the 24-h expression pattern, erCry4a remains the more likely cryptochrome to be involved in radical-pair-based magnetoreception, but at the present time, an involvement of erCry4b cannot be excluded.

Moderate static magnetic fields enhance antitumor CD8+ T cell function by promoting mitochondrial respiration

With the discovery of magnetoreceptor mechanisms in animals, it materialized the novel applications of controlling cell and animal behaviors using magnetic fields. T cells have shown to be sensitive to magnetic fields. Here, we reported that exposure to moderate SMFs (static magnetic fields) led to increased granule and cytokine secretion as well as ATP production and mitochondrial respiration from CD8⁺ T cells. These effects were inhibited by knocking down the Uqcrb and Ndufs6 genes of mitochondrial respiratory chain, whose transcriptions were regulated by candidate magnetoreceptor genes Isca1 and Cry1/Cry2. SMF exposure also promoted CD8⁺ T cell granule and cytokine secretion and repressed tumor growth in vivo. SMFs enhanced CD8⁺ T cell cytotoxicity, and the adoptive transfer into tumor-bearing mice resulted in enhanced antitumor effects. Collectively, our study suggests that moderate SMFs enhance CD8⁺ T cell cytotoxicity by promoting mitochondrial respiration and promoted the antitumor function of CD8⁺ T cells.

High spatial resolution multi-channel optically pumped atomic magnetometer based on a spatial light modulator

Ultra-sensitive multi-channel optically pumped atomic magnetometers based on the spin-exchange relaxation-free (SERF) effect are powerful tools for applications in the field of magnetic imaging. To simultaneously achieve ultra-high spatial resolution and ultra-high magnetic field sensitivity, we proposed a high-resolution multi-channel SERF atomic magnetometer for two-dimensional magnetic field measurements based on a digital micro-mirror device (DMD) as the spatial light modulator for a single vapor cell. Under the optimal experimental conditions obtained via spatial and temporal modulation of the probe light, we first demonstrated that the average sensitivity of the proposed 25-channel magnetometer was approximately 25fT/Hz^1/2 with a spatial resolution of 216µm. Then, we measured the magnetic field distribution generated by a gradient coil and compared the experimentally obtained distributions with those calculated via finite element simulation. The obtained g value of 99.2% indicated good agreement between our experimental results and the theoretical calculations, thereby confirming that our proposed multi-channel SERF magnetometer was effective at measuring magnetic field distributions with an ultra-high spatial resolution.

Evaluation of frequency magnetic field, static field, and Temozolomide on viability, free radical production and gene expression (p53) in the human glioblastoma cell line (A172)

Thirteen million cancer deaths and 21.7 million new cancer cases are expected in the world by 2030. Glioblastoma is the most common primary malignant tumor of the central nervous system which is the most lethal type of primary brain tumor in adults with the survival time of 12-15 months after the initial diagnosis. Glioblastoma is the most common and most malignant type of brain tumor, and despite surgery, chemotherapy and radiation treatment, the average survival of patients is about 14 months. The current research showed that the frequency magnetic field (FMF) and static magnetic field (SMF) can influence cancer cell proliferation and coupled with anticancer drugs may provide a new strategy for cancer therapy. At the present study, we investigated the effects of FMF (10 Hz, 50 G), SMF (50 G) and Temozolomide (200 μm) on viability, free radical production, and p53 followed by p53 protein expression in the human glioblastoma cell line (A172) by MTT, NBT, RT-PCR and Western blot. Results showed that the effect of Temozolomide (TMZ) with SMF and FMF together increased the cytotoxicity, free radical production, and p53 followed by p53 protein expression in the human glioblastoma cell line (A172).

Arabidopsis cryptochrome is responsive to Radiofrequency (RF) electromagnetic fields

How living systems respond to weak electromagnetic fields represents one of the major unsolved challenges in sensory biology. Recent evidence has implicated cryptochrome, an evolutionarily conserved flavoprotein receptor, in magnetic field responses of organisms ranging from plants to migratory birds. However, whether cryptochromes fulfill the criteria to function as biological magnetosensors remains to be established. Currently, theoretical predictions on the underlying mechanism of chemical magnetoreception have been supported by experimental observations that exposure to radiofrequency (RF) in the MHz range disrupt bird orientation and mammalian cellular respiration. Here we show that, in keeping with certain quantum physical hypotheses, a weak 7 MHz radiofrequency magnetic field significantly reduces the biological responsivity to blue light of the cryptochrome receptor cry1 in Arabidopsis seedlings. Using an in vivo phosphorylation assay that specifically detects activated cryptochrome, we demonstrate that RF exposure reduces conformational changes associated with biological activity. RF exposure furthermore alters cryptochrome-dependent plant growth responses and gene expression to a degree consistent with theoretical predictions. To our knowledge this represents the first demonstration of a biological receptor responding to RF exposure, providing important new implications for magnetosensing as well as possible future applications in biotechnology and medicine.

The Magnetic Receptor of Monascus ruber M7: Gene Clone and Its Heterologous Expression in Escherichia coli

It is well known that many organisms can perceive the magnetic field (MF), including the geomagnetic field, but how to feel MF is unclear. Recently, a study has claimed that a biological compass, namely a complex of the magnetic receptor (MagR) and blue light (BL) receptor (cryptochrome), has been found in Homo sapiens, Drosophila melanogaster, and Danaus plexippus, which may bring some new ideas to explore the mechanism of biomagnetism. Monascus spp. are edible filamentous fungi that can produce abundant beneficial secondary metabolites and have been used to produce food colorants for nearly 2000 years in the world, especially in China, Japan, and Korea. In this work, we firstly treated M. ruber M7 by BL (500 lux,465–467 nm), MF (5, 10, 30 mT), and the combination of MF and BL (MF-BL), respectively. The results revealed that, compared with the control (CK, neither BL nor MF), the MF alone had no effect on the growth and morphological characteristics of M7, but BL made the colonial diameters only 66.7% of CK’s and inhibited the formation of cleistothecia. Under MF-BL, the colony diameters were still 66.7% of CK’s, but the colonial growth and cleistothecia production inhibited by BL were partially restored. Then, we have found that the magR gene widely exists in the genomes of animals, plants, and microorganisms, and we have also discovered a magR gene in the M7 genome, hereinafter referred to mr-magR. Finally, the full-length cDNA of mr-magR was successfully cloned and expressed in Escherichia coli BL21 (DE3), and the Mr-MagR protein was purified by a Ni⁺-NTA column and identified by Western blot. These results have laid a foundation for further investigation on the relationship between Mr-MagR and BL receptor(s) that might exist in M7. According to a literature search, it is the first time to report magR in filamentous fungi.

Protein-protein interaction of the putative magnetoreceptor cryptochrome 4 expressed in the avian retina

Migratory birds can sense the Earth’s magnetic field and use it for orientation over thousands of kilometres. A light-dependent radical-pair mechanism associated with the visual system is currently discussed as the underlying mechanism of the magnetic compass sense. The blue light receptor cryptochrome 4 (Cry4) is considered as the most likely primary sensory protein that detects the geomagnetic field. Since the protein interaction partners of Cry4 are completely unknown at present, here, we aim to identify potential candidate interaction partners of Cry4 in the avian retina. We used the yeast-two-hybrid system to screen avian cDNA libraries for possible interaction partners of Cry4 in the European robin. The UAS-GAL yeast two hybrid system was applied to confirm a group of candidate Cry4 interaction partners. Six proteins were found to be particularly promising candidates for interacting with European robin Cry4. The identified genes code for guanine nucleotide-binding protein G(t) subunit alpha-2 (GNAT2), long-wavelength-sensitive opsin (LWS, also called iodopsin), guanine nucleotide-binding protein subunit gamma 10 (GNG10), potassium voltage-gated channel subfamily V member 2 (KCNV2), retinol binding protein 1 (RBP1) and retinal G protein-coupled receptor (RGR). All genes are known to be expressed in vertebrate retinae of different species. We conclude by discussing putative signalling pathways that could connect cryptochrome 4 to one or more of these 6 candidates.

Nanoscale magnetic imaging enabled by nitrogen vacancy centres in nanodiamonds labelled by iron-oxide nanoparticles

Nanodiamonds containing the nitrogen vacancy centre (NV) have a significant role in biosensing, bioimaging, drug delivery, and as biomarkers in fluorescence imaging, due to their photo-stability and biocompatibility. The optical read out of the NV unpaired electron spin has been used in diamond magnetometry to image living cells and magnetically labelled cells. Diamond magnetometry is mostly based on the use of bulk diamond with a large concentration of NV centres in a wide field fluorescence microscope equipped with microwave excitation. It is possible to correlate the fluorescence maps with the magnetic field maps of magnetically labelled cells with diffraction limit resolution. Nanodiamonds have not as yet been implemented to image magnetic fields within complex biological systems at the nanometre scale. Here we demonstrate the suitability of nanodiamonds to correlate the fluorescence map with the magnetic imaging map of magnetically labelled cells. Nanoscale optical images with 17 nm resolution of nanodiamonds labelling fixed cells bound to iron oxide magnetic nanoparticles are demonstrated by using a single molecule localisation microscope. Nanoscale magnetic field images of the magnetised magnetic nanoparticles spatially assigned to individual cells are superresolved by the NV centres within nanodiamonds conjugated with the magnetic nanoparticles with 20 nm resolutions. Our method offers a new platform for the super-resolution of optical magnetic imaging in biological samples conjugated with nanodiamonds and iron-oxide magnetic nanoparticles.

Magnetic Noise Enabled Biocompass

The discovery of magnetic protein provides a new understanding of a biocompass at the molecular level. However, the mechanism by which magnetic protein enables a biocompass is still under debate, mainly because of the absence of permanent magnetism in the magnetic protein at room temperature. Here, based on a widely accepted radical pair model of a biocompass, we propose a microscopic mechanism that allows the biocompass to operate without a finite magnetization of the magnetic protein in a biological environment. With the structure of the magnetic protein, we show that the magnetic fluctuation, rather than the permanent magnetism, of the magnetic protein can enable geomagnetic field sensing. An analysis of the quantum dynamics of our microscopic model reveals the necessary conditions for optimal sensitivity. Our work clarifies the mechanism by which magnetic protein enables a biocompass.

Effects and Mechanisms of Exogenous Electromagnetic Field on Bone Cells: A Review

Osteoporosis, fractures, and other bone diseases or injuries represent serious health problems in modern society. A variety of treatments including drugs, surgeries, physical therapies, etc. have been used to prevent or delay the progression of these diseases/injuries with limited effects. Electromagnetic field (EMF) has been used to non-invasively treat bone diseases, such as fracture and osteoporosis, for many years. However, because a variety of cellular and molecular events can be affected by EMF with various parameters, the precise bioeffects and underlying mechanisms of specific EMF on bone cells are still obscure. Here, we summarize the common therapeutic parameters (frequency and intensity) of major types of EMF used to treat bone cells taken from 32 papers we selected from the PubMed database published in English from 1991 to 2018. Briefly, pulse EMF promotes the proliferation of osteoblasts when its frequency is 7.5-15 Hz or 50-75 Hz and the intensity is 0.40-1.55 mT or 3.8-4 mT. Sinusoidal EMF, with 0.9-4.8 mT and 45-60 Hz, and static magnetic field with 0.1-0.4 mT or 400 mT, can promote osteoblast differentiation and maturation. Finally, we summarize the latest advances on the molecular signaling pathways influenced by EMF in osteoblasts and osteoclasts. A variety of molecules such as adenosine receptors, calcium channels, BMP2, Notch, Wnt1, etc., can be influenced by EMF in osteoblasts. For osteoclasts, EMF affects RANK, NF-κB, MAPK, etc. We speculate that EMF with different frequencies and intensities exert distinct bioeffects on specific bone cells. More high-quality work is required to explore the detailed effects and underlying mechanisms of EMF on bone cells/skeleton to optimize the application of EMF on bone diseases/injuries. Bioelectromagnetics. 2020;41:263-278 © 2020 Bioelectromagnetics Society.

Propulsive nanomachines: the convergent evolution of archaella, flagella and cilia

Echoing the repeated convergent evolution of flight and vision in large eukaryotes, propulsive swimming motility has evolved independently in microbes in each of the three domains of life. Filamentous appendages – archaella in Archaea, flagella in Bacteria and cilia in Eukaryotes – wave, whip or rotate to propel microbes, overcoming diffusion and enabling colonization of new environments. The implementations of the three propulsive nanomachines are distinct, however: archaella and flagella rotate, while cilia beat or wave; flagella and cilia assemble at their tips, while archaella assemble at their base; archaella and cilia use ATP for motility, while flagella use ion-motive force. These underlying differences reflect the tinkering required to evolve a molecular machine, in which pre-existing machines in the appropriate contexts were iteratively co-opted for new functions and whose origins are reflected in their resultant mechanisms. Contemporary homologies suggest that archaella evolved from a non-rotary pilus, flagella from a non-rotary appendage or secretion system, and cilia from a passive sensory structure. Here, we review the structure, assembly, mechanism and homologies of the three distinct solutions as a foundation to better understand how propulsive nanomachines evolved three times independently and to highlight principles of molecular evolution.

One Actor, Multiple Roles: The Performances of Cryptochrome in Drosophila

Cryptochromes (CRYs) are flavoproteins that are sensitive to blue light, first identified in Arabidopsis and then in Drosophila and mice. They are evolutionarily conserved and play fundamental roles in the circadian clock of living organisms, enabling them to adapt to the daily 24-h cycles. The role of CRYs in circadian clocks differs among different species: in plants, they have a blue light-sensing activity whereas in mammals they act as light-independent transcriptional repressors within the circadian clock. These two different functions are accomplished by two principal types of CRYs, the light-sensitive plant/insect type 1 CRY and the mammalian type 2 CRY acting as a negative autoregulator in the molecular circadian clockwork. Drosophila melanogaster possesses just one CRY, belonging to type 1 CRYs. Nevertheless, this single CRY appears to have different functions, specific to different organs, tissues, and even subset of cells in which it is expressed. In this review, we will dissect the multiple roles of this single CRY in Drosophila, focusing on the regulatory mechanisms that make its pleiotropy possible.

The Evolution History of Fe-S Cluster A-Type Assembly Protein Reveals Multiple Gene Duplication Events and Essential Protein Motifs

Iron-sulfur (Fe-S) clusters play important roles in electron transfer, metabolic and biosynthetic reactions, and the regulation of gene expression. Understanding the biogenesis of Fe-S clusters is therefore relevant to many fields. In the complex process of Fe-S protein formation, the A-type assembly protein (ATAP) family, which consists of several subfamilies, plays an essential role in Fe-S cluster formation and transfer and is highly conserved across the tree of life. However, the taxonomic distribution, motif compositions, and the evolutionary history of the ATAP subfamilies are not well understood. To address these problems, our study investigated the taxonomic distribution of 321 species from a broad cross-section of taxa. Then, we identified common and specific motifs in multiple ATAP subfamilies to explain the functional conservation and nonredundancy of the ATAPs, and a novel, essential motif was found in Eumetazoa IscA1, which has a newly found magnetic function. Finally, we used phylogenetic analytical methods to reconstruct the evolution history of this family. Our results show that two types of ErpA proteins (nonproteobacteria-type ErpA1 and proteobacteria-type ErpA2) exist in bacteria. The ATAP family, consisting of seven subfamilies, can be further classified into two types of ATAPs. Type-I ATAPs include IscA, SufA, HesB, ErpA1, and IscA1, with an ErpA1-like gene as their last common ancestor, whereas type-II ATAPs consist of ErpA2 and IscA2, duplicated from an ErpA2-like gene. During the mitochondrial endosymbiosis, IscA became IscA1 in eukaryotes and ErpA2 became IscA2 in eukaryotes, respectively.

Sonogenetic Modulation of Cellular Activities Using an Engineered Auditory-Sensing Protein

Biomolecules that respond to different external stimuli enable the remote control of genetically modified cells. We report herein a sonogenetic approach that can manipulate target cell activities by focused ultrasound stimulation. This system requires an ultrasound-responsive protein derived from an engineered auditory-sensing protein prestin. Heterologous expression of mouse prestin containing two parallel amino acid substitutions, N7T and N308S, that frequently exist in prestins from echolocating species endowed transfected mammalian cells with the ability to sense ultrasound. An ultrasound pulse of low frequency and low pressure efficiently evoked cellular calcium responses after transfecting with prestin(N7T, N308S). Moreover, pulsed ultrasound can also noninvasively stimulate target neurons expressing prestin(N7T, N308S) in deep regions of mouse brains. Our study delineates how an engineered auditory-sensing protein can cause mammalian cells to sense ultrasound stimulation. Moreover, our sonogenetic tools will serve as new strategies for noninvasive therapy in deep tissues.

Genomic and Phenotypic Analyses Reveal Mechanisms Underlying Homing Ability in Pigeon

The homing pigeon was selectively bred from the domestic pigeon for a homing ability over long distances, a very fascinating but complex behavioral trait. Here, we generate a total of 95 whole genomes from diverse pigeon breeds. Comparing the genomes from the homing pigeon population with those from other breeds identifies candidate positively selected genes, including many genes involved in the central nervous system, particularly spatial learning and memory such as LRP8. Expression profiling reveals many neuronal genes displaying differential expression in the hippocampus, which is the key organ for memory and navigation and exhibits significantly larger size in the homing pigeon. In addition, we uncover a candidate gene GSR (encoding glutathione-disulfide reductase) experiencing positive selection in the homing pigeon. Expression profiling finds that GSR is highly expressed in the wattle and visual pigment cell layer, and displays increased expression levels in the homing pigeon. In vitro, a magnetic field stimulates increases in calcium ion concentration in cells expressing pigeon GSR. These findings support the importance of the hippocampus (functioning in spatial memory and navigation) for homing ability, and the potential involvement of GSR in pigeon magnetoreception.

Possible Mechanism for Synchronized Detection of Weak Magnetic Fields by Nerve Cells

We propose that biological systems may detect static and slowly varying magnetic fields by the modification of the timing of firing of adjacent nerve cells through the local influence of the magnetic field generated by current from one cell's firing on its nearest neighbors. The time delay of an adjacent nerve cell pulse with respect to the initial clock nerve cell pulse could serve as a signal for sensing the magnitude and direction of the magnetic field in a direction perpendicular to the current flows in the cells. It has been shown that changes in static magnetic fields modify concentrations of reactive oxygen species, calcium, pH, the growth rates of fibrosarcoma cells, and membrane potentials. These are linked to changes in membrane potentials that can either inhibit or accelerate the firing rate of pacemaker or clock cells. This mechanism may have applications to animals' use of magnetic fields for navigation or other purposes, possibly in conjunction with other mechanisms. Bioelectromagnetics. © 2020 Bioelectromagnetics Society.