A defective SERCA1 protein is responsible for congenital pseudomyotonia in Chianina cattle

Antitumor Effect of Berberine Analogs in a Canine Mammary Tumor Cell Line and in Zebrafish Reporters via Wnt/β-Catenin and Hippo Pathways

The heterogeneous nature of human breast cancer (HBC) can still lead to therapy inefficacy and high lethality, and new therapeutics as well as new spontaneous animal models are needed to benefit translational HBC research. Dogs are primarily investigated since they spontaneously develop tumors that share many features with human cancers. In recent years, different natural phytochemicals including berberine, a plant alkaloid, have been reported to have antiproliferative activity in vitro in human cancers and rodent animal models. In this study, we report the antiproliferative activity and mechanism of action of berberine, its active metabolite berberrubine, and eight analogs, on a canine mammary carcinoma cell line and in transgenic zebrafish models. We demonstrate both in vitro and in vivo the significant effects of specific analogs on cell viability via the induction of apoptosis, also identifying their role in inhibiting the Wnt/β-catenin pathway and activating the Hippo signals with a downstream reduction in CTGF expression. In particular, the berberine analogs NAX035 and NAX057 show the highest therapeutic efficacy, deserving further analyses to elucidate their mechanism of action more in detail, and in vivo studies on spontaneous neoplastic diseases are needed, aiming at improving veterinary treatments of cancer as well as translational cancer research.

Differential Analysis of Gly211Val and Gly286Val Mutations Affecting Sarco(endo)plasmic Reticulum Ca2+-ATPase (SERCA1) in Congenital Pseudomyotonia Romagnola Cattle

Congenital pseudomyotonia in cattle (PMT) is a rare skeletal muscle disorder, clinically characterized by stiffness and by delayed muscle relaxation after exercise. Muscle relaxation impairment is due to defective content of the Sarco(endo)plasmic Reticulum Ca²⁺ ATPase isoform 1 (SERCA1) protein, caused by missense mutations in the ATP2A1 gene. PMT represents the only mammalian model of human Brody myopathy. In the Romagnola breed, two missense variants occurring in the same allele were described, leading to Gly211Val and Gly286Val (G211V/G286V) substitutions. In this study, we analyzed the consequences of G211V and G286V mutations. Results support that the reduced amount of SERCA1 is a consequence of the G211V mutation, the G286V mutation almost being benign and the ubiquitin–proteasome system (UPS) being involved. After blocking the proteasome using a proteasome inhibitor, we found that the G211V mutant accumulates in cells at levels comparable to those of WT SERCA1. Our conclusion is that G211/286V mutations presumably originate in a folding-defective SERCA1 protein, recognized and diverted to degradation by UPS, although still catalytically functional, and that the main role is played by G211V mutation. Rescue of mutated SERCA1 to the sarcoplasmic reticulum membrane can re-establish resting cytosolic Ca²⁺ concentration and prevent the appearance of pathological signs, paving the way for a possible therapeutic approach against Brody disease.

Sarcoplasmic Reticulum from Horse Gluteal Muscle Is Poised for Enhanced Calcium Transport

We have analyzed the enzymatic activity of the sarcoplasmic reticulum (SR) Ca²⁺-transporting ATPase (SERCA) from the horse gluteal muscle. Horses are bred for peak athletic performance yet exhibit a high incidence of exertional rhabdomyolysis, with elevated levels of cytosolic Ca²⁺ proposed as a correlative linkage. We recently reported an improved protocol for isolating SR vesicles from horse muscle; these horse SR vesicles contain an abundant level of SERCA and only trace-levels of sarcolipin (SLN), the inhibitory peptide subunit of SERCA in mammalian fast-twitch skeletal muscle. Here, we report that the in vitro Ca²⁺ transport rate of horse SR vesicles is 2.3 ± 0.7-fold greater than rabbit SR vesicles, which express close to equimolar levels of SERCA and SLN. This suggests that horse myofibers exhibit an enhanced SR Ca²⁺ transport rate and increased luminal Ca²⁺ stores in vivo. Using the densitometry of Coomassie-stained SDS-PAGE gels, we determined that horse SR vesicles express an abundant level of the luminal SR Ca²⁺ storage protein calsequestrin (CASQ), with a CASQ-to-SERCA ratio about double that in rabbit SR vesicles. Thus, we propose that SR Ca²⁺ cycling in horse myofibers is enhanced by a reduced SLN inhibition of SERCA and by an abundant expression of CASQ. Together, these results suggest that horse muscle contractility and susceptibility to exertional rhabdomyolysis are promoted by enhanced SR Ca²⁺ uptake and luminal Ca²⁺ storage.

Double-Outlet Right Ventricle in a Chianina Calf

Congenital heart defects have been occasionally reported in cattle and ventricular septal defect represents the most frequently encountered anomaly. The double-outlet right ventricle is a rare congenital ventriculoarterial malformation reported only in certain cattle breeds. We describe this rare and complex congenital cardiac malformation observed in a 10-day-old male Chianina calf. Clinical examination showed tachycardia, tachypnea, jugular pulses, cyanotic mucous membranes and a right apical systolic murmur. Transthoracic echocardiography revealed severe dilation of the right-sided cardiac chambers with a markedly hypoplastic left ventricle. Both aorta and pulmonary artery leaving the right ventricle in parallel alignment with the tricuspid valve were suggestive of a dual-outlet right ventricle. Interventricular and interatrial septal defects were also visualized. Post-mortem examination confirmed the echocardiographic findings. To the authors' knowledge, a similar complex congenital cardiac malformation has not been reported in calves of the Chianina breed to date.

Effect of feed restriction timing on live performance, breast myopathy occurrence, and muscle fiber degeneration in 2 broiler chicken genetic lines

During recent years, research on meat quality in poultry has aimed to evaluate the presence and consequences of breast myopathies as well as the factors which can affect their occurrence by modifying the growth rate. A total of 900 broiler chickens were reared until slaughter (48 D) to evaluate the effect of 2 genetic lines (A vs. B) and feeding plans (ad libitum [AL], early restricted [ER], from 13 to 23 D of age, and late restricted [LR], from 27 to 37 D of age; restriction rate: 80%) on performance, meat quality, and breast muscle myopathies. Calsequestrin and vascular endothelial growth factor (VEGF) expressions, and muscle fiber degeneration (MFD) were recorded at 22, 36, and 48 D. Chickens in the AL treatment had greater final live (P < 0.01) and carcass weights and proportion of pectoralis major muscle (P = 0.04) compared to chickens in the LR treatment, whereas chickens in the ER treatment had intermediate final live (3,454 g) and carcass weights, and proportion of pectoralis major muscle (25.6%). Chickens of line A were heavier than chickens of line B (P < 0.001), and had a greater feed conversion rate. Chickens of line A also had a greater dressing out percentage (P < 0.001), but a lower proportion of pectoralis major muscle (P = 0.04), as well as a greater meat pH (P < 0.001), meat cooking losses (P < 0.01), and shear force of the pectoralis major muscle (P = 0.03). Calsequestrin and VEGF mRNA were significantly lower in ER and LR chickens compared to AL chickens after feed restriction and during refeeding (P < 0.05). MFD scores increased with chicken age (P < 0.001) and differed between genetic lines (P < 0.001). Neither feeding plan nor genetic line affected the occurrence of white striping or wooden breast condition.

Paradoxical pseudomyotonia in English Springer and Cocker Spaniels

Background

Paramyotonia congenita and Brody disease are well‐described conditions in humans, characterized by exercise‐induced myotonic‐like muscle stiffness. A syndrome similar to Brody disease has been reported in cattle. Reports of a similar syndrome in dogs are scarce.

Objectives

To define and describe the clinical, diagnostic, and genetic features and disease course of paradoxical pseudomyotonia in Spaniel dogs.

Animals

Seven client‐owned dogs (4 English Springer Spaniels and 3 English Cocker Spaniels) with clinically confirmed episodes of exercise‐induced generalized myotonic‐like muscle stiffness.

Methods

Sequential case study.

Results

All dogs were <24 months of age at onset. The episodes of myotonic‐like generalized muscle stiffness always occurred with exercise, and spontaneously resolved with rest in <45 seconds in all but 1 dog. Extreme outside temperatures seemed to considerably worsen episode frequency and severity in most dogs. Complete blood count, serum biochemistry including electrolytes, urinalysis, brain magnetic resonance imaging, cerebrospinal fluid analysis, electromyography, motor nerve conduction velocity, ECG, and echocardiography were unremarkable. Muscle biopsy samples showed moderate but nonspecific muscle atrophy. The episodes seemed to remain stable or decrease in severity and frequency in 6/7 dogs, and often could be decreased or prevented by avoiding the episode triggers. The underlying genetic cause is not identified yet, because no disease‐causing variants could be found in the coding sequence or splice sites of the 2 major candidate genes, SCN4A and ATP2A1.

Conclusions and Clinical Importance

Paradoxical pseudomyotonia is a disease affecting Spaniels. It is of variable severity but benign in most cases.

Age-dependent variations in the expression of myosin isoforms and myogenic factors during the involution of the proximal sesamoidean ligament of sheep

In ungulates the stability of the fetlock joint is dependent on several muscles, which are exposed to high stress and strain. Among those muscles, the proximal sesamoidean ligament or PSL (also known as the suspensory ligament or Ruini's elasto-tendinous organ) is organized at birth in layers of muscle fibres alternated with abundant tendinous tissue that, during the postnatal development, becomes the predominant tissue. In this study we analysed the PSL of the sheep at the age of 1, 30 and 180 days and determined the expression of several genes which either (a) are markers of muscle fibre growth and maturation, or (b) play a role as signal molecules. We observed an accelerated maturation, as indicated by the transition of MyHC isoform expression towards the slow isoforms and a reduced regenerative potential indicated by the low Pax7 expression and the altered Wnt signalling. We also found a specific myogenic expression pattern of MyoD, Myf5 and Myogenin in the developing PSL and high mRNA levels of specific fibrogenic factors, as TGF-β1, that, undoubtedly, stimulate the growth of connective tissue. Our observations confirmed, at molecular level, the peculiarity of the fast involution observed in PSL a muscle that undergoes a very specific active differentiation process during early development, which implies myofibres involution and their replacement with connective tissue.

HDAC Inhibition Improves the Sarcoendoplasmic Reticulum Ca2+-ATPase Activity in Cardiac Myocytes

SERCA2a is the Ca²⁺ ATPase playing the major contribution in cardiomyocyte (CM) calcium removal. Its activity can be regulated by both modulatory proteins and several post-translational modifications. The aim of the present work was to investigate whether the function of SERCA2 can be modulated by treating CMs with the histone deacetylase (HDAC) inhibitor suberanilohydroxamic acid (SAHA). The incubation with SAHA (2.5 µM, 90 min) of CMs isolated from rat adult hearts resulted in an increase of SERCA2 acetylation level and improved ATPase activity. This was associated with a significant improvement of calcium transient recovery time and cell contractility. Previous reports have identified K464 as an acetylation site in human SERCA2. Mutants were generated where K464 was substituted with glutamine (Q) or arginine (R), mimicking constitutive acetylation or deacetylation, respectively. The K464Q mutation ameliorated ATPase activity and calcium transient recovery time, thus indicating that constitutive K464 acetylation has a positive impact on human SERCA2a (hSERCA2a) function. In conclusion, SAHA induced deacetylation inhibition had a positive impact on CM calcium handling, that, at least in part, was due to improved SERCA2 activity. This observation can provide the basis for the development of novel pharmacological approaches to ameliorate SERCA2 efficiency.

Structural study of skeletal muscle fibres in healthy and pseudomyotonia affected cattle

Cattle congenital pseudomyotonia (PMT), recognized as naturally occurring animal model of human Brody disease, is an inherited recessive autosomal muscular disorder due to missense mutations in ATP2A1 gene, encoding sarco(endo)plasmic reticulum Ca(2+)-ATPase protein, isoform 1 (SERCA1). PMT has been described in the Chianina and Romagnola italian cattle breeds and as a single case in Dutch improved Red and White cross-breed. The genetic defect turned out to be heterogeneous in different cattle breeds, even though clinical symptoms were homogeneous. Skeletal muscles of affected animals are characterized by a selective deficiency of SERCA1 in sarcoplasmic reticulum (SR) membranes. Recently, we provided evidence that in Chianina breed, the ubiquitin proteasome system is responsible for SERCA1 mutant premature disposal, even when the mutation does not affect the catalytic properties of the pump. Results presented here show that all SERCA1 mutants described until now, although expressed at low level, are correctly targeted to SR membranes. Ultrastructural studies confirm that in pathological muscle fibres, structure, as well as triads, is well preserved. All together these results suggest that a possible therapeutical approach based on the rescue of the defective protein at SR membranes could be hypothesized. Only fully functionally active missense mutants, whem located at the SR membrane could restore the efficient control of Ca(2+) homeostasis and prevent the appearance of the pathological signs. Moreover, these data demonstrate the increasing importance of domestic animals as genetic models of human pathologies.

Dystonia and Paroxysmal Dyskinesias: Under-Recognized Movement Disorders in Domestic Animals? A Comparison with Human Dystonia/Paroxysmal Dyskinesias

Dystonia is defined as a neurological syndrome characterized by involuntary sustained or intermittent muscle contractions causing twisting, often repetitive movements, and postures. Paroxysmal dyskinesias are episodic movement disorders encompassing dystonia, chorea, athetosis, and ballism in conscious individuals. Several decades of research have enhanced the understanding of the etiology of human dystonia and dyskinesias that are associated with dystonia, but the pathophysiology remains largely unknown. The spontaneous occurrence of hereditary dystonia and paroxysmal dyskinesia is well documented in rodents used as animal models in basic dystonia research. Several hyperkinetic movement disorders, described in dogs, horses and cattle, show similarities to these human movement disorders. Although dystonia is regarded as the third most common movement disorder in humans, it is often misdiagnosed because of the heterogeneity of etiology and clinical presentation. Since these conditions are poorly known in veterinary practice, their prevalence may be underestimated in veterinary medicine. In order to attract attention to these movement disorders, i.e., dystonia and paroxysmal dyskinesias associated with dystonia, and to enhance interest in translational research, this review gives a brief overview of the current literature regarding dystonia/paroxysmal dyskinesia in humans and summarizes similar hereditary movement disorders reported in domestic animals.

Atypical nuclear abnormalities in a patient with Brody disease

Brody disease was first described as a benign pseudo-myotonic disorder with muscular stiffness, which increased with exercise. Biochemical and genetic studies have pointed out its close relationship to a functional defect of the fast-twitch sarcoplasmic reticulum Ca(++) ATPase pump (SERCA1) encoded by the ATP2A1 gene located on chromosome 16. The histopathological features in this form of myopathy were generally described as non-specific, i.e. moderate degree of type 2 fibre atrophy and excess of internal nuclei. We here present the clinical and histopathological features of a patient with Brody disease over a 19-year follow-up period. This patient had two heterozygous ATP2A1 mutations and complained about muscle stiffness immediately after effort. He had suffered from this since early childhood and exhibited clinical symptoms mimicking myotonia. Histological, ultrastructural and cytogenetic analyses revealed morphologically abnormal nuclei with polyploidy. In this report, we discuss the possible links between the consequences of the genetic abnormality and the peculiar aspect of the nuclei.

Inhibition of ubiquitin proteasome system rescues the defective sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA1) protein causing Chianina cattle pseudomyotonia

A missense mutation in ATP2A1 gene, encoding sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA1) protein, causes Chianina cattle congenital pseudomyotonia, an exercise-induced impairment of muscle relaxation. Skeletal muscles of affected cattle are characterized by a selective reduction of SERCA1 in sarcoplasmic reticulum membranes. In this study, we provide evidence that the ubiquitin proteasome system is involved in the reduced density of mutated SERCA1. The treatment with MG132, an inhibitor of ubiquitin proteasome system, rescues the expression level and membrane localization of the SERCA1 mutant in a heterologous cellular model. Cells co-transfected with the Ca(2+)-sensitive probe aequorin show that the rescued SERCA1 mutant exhibits the same ability of wild type to maintain Ca(2+) homeostasis within cells. These data have been confirmed by those obtained ex vivo on adult skeletal muscle fibers from a biopsy from a pseudomyotonia-affected subject. Our data show that the mutation generates a protein most likely corrupted in proper folding but not in catalytic activity. Rescue of mutated SERCA1 to sarcoplasmic reticulum membrane can re-establish resting cytosolic Ca(2+) concentration and prevent the appearance of pathological signs of cattle pseudomyotonia.

Post-natal heart adaptation in a knock-in mouse model of calsequestrin 2-linked recessive catecholaminergic polymorphic ventricular tachycardia

Cardiac calsequestrin (CASQ2) contributes to intracellular Ca(2+) homeostasis by virtue of its low-affinity/high-capacity Ca(2+) binding properties, maintains sarcoplasmic reticulum (SR) architecture and regulates excitation-contraction coupling, especially or exclusively upon β-adrenergic stimulation. Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disease associated with cardiac arrest in children or young adults. Recessive CPVT variants are due to mutations in the CASQ2 gene. Molecular and ultra-structural properties were studied in hearts of CASQ2(R33Q/R33Q) and of CASQ2(-/-) mice from post-natal day 2 to week 8. The drastic reduction of CASQ2-R33Q is an early developmental event and is accompanied by down-regulation of triadin and junctin, and morphological changes of jSR and of SR-transverse-tubule junctions. Although endoplasmic reticulum stress is activated, no signs of either apoptosis or autophagy are detected. The other model of recessive CPVT, the CASQ2(-/-) mouse, does not display the same adaptive pattern. Expression of CASQ2-R33Q influences molecular and ultra-structural heart development; post-natal, adaptive changes appear capable of ensuring until adulthood a new pathophysiological equilibrium.

Microarray gene expression profiling of neural tissues in bovine spastic paresis

Background

Bovine Spastic Paresis (BSP) is a neuromuscular disorder which affects both male and female cattle. BSP is characterized by spastic contraction and overextension of the gastrocnemious muscle of one or both limbs and is associated with a scarce increase in body weight. This disease seems to be caused by an autosomal and recessive gene, with incomplete penetration, although no genes clearly involved with its onset have been so far identified. We employed cDNA microarrays to identify metabolic pathways affected by BSP in Romagnola cattle breed. Investigation of those pathways at the genome level can help to understand this disease.

Results

Microarray analysis of control and affected individuals resulted in 268 differentially expressed genes. These genes were subjected to KEGG pathway functional clustering analysis, revealing that they are predominantly involved in Cell Communication, Signalling Molecules and Interaction and Signal Transduction, Diseases and Nervous System classes. Significantly enriched KEGG pathway’s classes for the differentially expressed genes were calculated; interestingly, all those significantly under-expressed in the affected samples are included in Neurodegenerative Diseases. To identify genome locations possibly harbouring gene(s) involved in the disease, the chromosome distribution of the differentially expressed genes was also investigated.

Conclusions

The cDNA microarray we used in this study contains a brain library and, even if carrying an incomplete transcriptome representation, it has proven to be a valuable tool allowing us to add useful and new information to a poorly studied disease. By using this tool, we examined nearly 15000 transcripts and analysed gene pathways affected by the disease. Particularly, our data suggest also a defective glycinergic synaptic transmission in the development of the disease and an alteration of calcium signalling proteins. We provide data to acquire knowledge of a genetic disease for which literature still presents poor results and that could be further and specifically analysed in the next future. Moreover this study, performed in livestock, may also harbour molecular information useful for understanding human diseases.

Pseudomyotonia in Romagnola cattle caused by novel ATP2A1 mutations

Background

Bovine congenital pseudomyotonia (PMT) is an impairment of muscle relaxation induced by exercise preventing animals from performing rapid movements. Forms of recessively inherited PMT have been described in different cattle breeds caused by two independent mutations in ATP2A1 encoding a skeletal-muscle Ca²⁺-ATPase (SERCA1). We observed symptoms of congenital PMT in four related Romagnola beef cattle from Italy and evaluated SERCA1 activity and scanned ATP2A1 for possible causative mutations.

Results

We obtained four PMT affected Romagnola cattle and noted striking clinical similarities to the previously described PMT cases in other cattle breeds. The affected animals had a reduced SERCA1 activity in the sarcoplasmic reticulum. A single affected animal was homozygous for a novel complex variant in ATP2A1 exon 8 (c.[632 G>T; 857 G>T]). Three out of four cases were compound heterozygous for the newly identified exon 8 variant and the exon 6 variant c.491 G>A(p. Arg146Gly), which has previously been shown to cause PMT in Chianina cattle. Pedigree analysis showed that the exon 8 double mutation event dates back to at least 1978. Both nucleotide substitutions are predicted to alter the SERCA1 amino acid sequence (p.[(Gly211Val; Gly284Val)]), affect highly conserved residues, in particular the actuator domain of SERCA1.

Conclusion

Clinical, biochemical and DNA analyses confirmed the initial hypothesis. We provide functional and genetic evidence that one novel and one previously described ATP2A1 mutation lead to a reduced SERCA1 activity in skeletal muscles and pseudomyotonia in affected Romagnola cattle. Selection against these mutations can now be used to eliminate the mutant alleles from the Romagnola breed.

Frequency of bovine congenital pseudomyotonia carriers in selected Italian Chianina sires

Bovine congenital pseudomyotonia (PMT) is a genetic disease in Chianina and other breeds of cattle that induces muscular stiffness. PMT in the Chianina breed is caused by a missense mutation in exon 6 of the ATP2A1 gene, which encodes the SERCA1 pump. In this study, the prevalence of PMT carriers and the frequency of the deleterious PMT allele in selected subpopulations of the Chianina breed were estimated. The prevalence of PMT carriers among ranked Chianina sires used for artificial insemination in the years 2007-2011 was 13.6%. The frequency of PMT carriers in young bull calves born in the period January 2007 to June 2011 selected for a performance testing programme was 13.4%. Selective breeding against this genetic defect is restricted to males only and therefore is predicted to require at least seven generations to eradicate PMT.

Crystal structure of sarcoplasmic reticulum Ca2+-ATPase (SERCA) from bovine muscle

The SERCA pump, a membrane protein of about 110kDa, transports two Ca(2+) ions per ATP hydrolyzed from the cytoplasm to the lumen of the sarcoplasmic reticulum. In muscle cells, its ability to remove Ca(2+) from the cytosol induces relaxation. The transport mechanism employed by the enzyme from rabbit muscle has been extensively studied, and several crystal structures representing different conformational states are available. However, no structure of the pump from other sources is known. In this paper we describe the crystal structure of the bovine enzyme, crystallized in the E1 conformation and determined at 2.9Å resolution. The overall molecular model is very similar to that of the rabbit enzyme, as expected by the high amino acid sequence identity. Nevertheless, the bovine enzyme has reduced catalytic activity with respect to the rabbit enzyme. Subtle structural modifications, in particular in the region of the long loop that protrudes into the SR lumen connecting transmembrane α-helices M7 and M8, may explain the difference.

Overexpression of histidine-rich calcium binding protein in equine ventricular myocardium

Histidine-rich calcium binding protein (HRC) is a high capacity, low affinity Ca(2+) binding protein, specifically expressed in striated muscles of mammals. In rabbit skeletal and cardiac muscles, HRC binds to sarcoplasmic reticulum (SR) membranes via triadin, a junctional SR protein. Recently, a potential role in heart failure and arrhythmogenesis has been assigned to HRC due to its activity as regulator of SR Ca(2+) uptake and Ca(2+) release. HRC might play a particularly relevant role in the equine heart, given its slower resting heart rate (20-35 beats/min) and longer action potential duration (APD) (0.6-1.0 s) than are found in other mammals. The results from this study showed for the first time direct evidence that HRC protein in equine cardiac muscle was expressed in association with the SR membranes and that HRC transcriptional activity was three times higher in the ventricles compared to the atria. The predominance of HRC mRNA up-regulation in ventricular myocardium was specific to the horse heart, since a more even distribution between atria and ventricles was found in animals of similar body size or species, such as cattle or domestic donkeys.

Endoplasmic-reticulum calcium depletion and disease

The endoplasmic reticulum (ER) as an intracellular Ca(2+) store not only sets up cytosolic Ca(2+) signals, but, among other functions, also assembles and folds newly synthesized proteins. Alterations in ER homeostasis, including severe Ca(2+) depletion, are an upstream event in the pathophysiology of many diseases. On the one hand, insufficient release of activator Ca(2+) may no longer sustain essential cell functions. On the other hand, loss of luminal Ca(2+) causes ER stress and activates an unfolded protein response, which, depending on the duration and severity of the stress, can reestablish normal ER function or lead to cell death. We will review these various diseases by mainly focusing on the mechanisms that cause ER Ca(2+) depletion.

Analysis of a zebrafish behavioral mutant reveals a dominant mutation in atp2a1/SERCA1

Zebrafish embryos demonstrate robust swimming behavior, which consists of smooth, alternating body bends. In contrast, several motility mutants have been identified that perform sustained, bilateral trunk muscle contractions which result in abnormal body shortening. Unlike most of these mutants, accordion (acc)(dta5) demonstrates a semidominant effect: Heterozygotes exhibit a distinct but less severe phenotype than homozygotes. Using molecular-genetic mapping and candidate gene analysis, we determined that acc(dta5) mutants harbor a novel mutation in atp2a1, which encodes SERCA1, a calcium pump important for muscle relaxation. Previous studies have shown that eight other acc alleles compromise SERCA1 function, but these alleles were all reported to be recessive. Quantitative behavioral assays, complementation testing, and analysis of molecular models all indicate that the acc(dta5) mutation diminishes SERCA1 function to a greater degree than other acc alleles through either haploinsufficient or dominant-negative molecular mechanisms. Since mutation of human ATP2A1 results in Brody disease, an exercise-induced impairment of muscle relaxation, acc(dta5) mutants may provide a particularly sensitive model of this disorder.

Pseudomyotonia, a muscle function disorder associated with an inherited ATP2A1 (SERCA1) defect in a Dutch Improved Red and White cross-breed calf

A Dutch Improved Red and White cross-breed heifer calf was evaluated for a muscular disorder resulting in exercise induced muscle stiffness. Clinical findings included generalized exercise-induced muscle spasms with normal response to muscle percussion. Electromyography showed no myotonic discharges, thus ruling out myotonia. Whereas histological examination of muscle tissue was unremarkable, Ca(2+)-ATPase activity of sarcoplasmatic reticulum membranes (SERCA1) was markedly decreased compared to control animals. Mutation analysis revealed the presence of a missense mutation in the ATP2A1 gene encoding the SERCA1 protein (p.Arg559Cys). The present case presents similarities to human Brody's disease, but also to pseudomyotonia and congenital muscular dystonia previously described in different cattle breeds.

Evidence for a new allele at the SERCA1 locus affecting pork meat quality in part through the imbalance of Ca2+ homeostasis

Sarcoendoplasmic reticulum Ca2+-ATPase 1 (SERCA1) as a Ca2+ release channel plays a key role in the relaxation of skeletal muscle through pumping cytosolic Ca2+ into the SR (sarcoplasmic reticulum). In this study, a novel single nucleotide polymorphism (SNP) in exon 8 (C > T) was detected by tetra-primer ARMS-PCR and the tissue expression pattern of SERCA1 was analyzed in eleven tissues. A model of primary skeletal muscle cells in vitro exposed to dexamethasone (DEX, a synthetic corticosteroid) was also employed to determine whether stress hormones cause an increase in intracellular Ca2+ concentration that is associated with alteration in SERCA1 and in turn subsequently affect meat quality. The results showed that the CC genotype has lower content intramuscular fat and higher water than pig carrying the genotype CT and CC. In addition, the additive effects were both significantly (P < 0.05) and allele T seemed to be associate with increase in intramuscular fat, while decrease in water content. Accompanied with previous studies, the high abundance of porcine SERCA1 was found in skeletal muscle tissue. DEX markedly down-regulated the expression of SERCA1, leading to Ca2+ overload. Furthermore, the imbalance of Ca2+ homeostasis up-regulated the transcription level of Calpain1. Taken together, we demonstrated a novel mechanism that the changes in expression of SERCA1 potential disturb the normal Ca2+ channel as well as the balance of Ca2+ homeostasis and which in turn finally activated Ca2+-dependent proteases such as Calpain1 which could affect meat quality.

Calcium Pumps in Health and Disease

Ca2+-ATPases (pumps) are key actors in the regulation of Ca2+ in eukaryotic cells and are thus essential to the correct functioning of the cell machinery. They have high affinity for Ca2+ and can efficiently regulate it down to very low concentration levels. Two of the pumps have been known for decades (the SERCA and PMCA pumps); one (the SPCA pump) has only become known recently. Each pump is the product of a multigene family, the number of isoforms being further increased by alternative splicing of the primary transcripts. The three pumps share the basic features of the catalytic mechanism but differ in a number of properties related to tissue distribution, regulation, and role in the cellular homeostasis of Ca2+. The molecular understanding of the function of the pumps has received great impetus from the solution of the three-dimensional structure of one of them, the SERCA pump. These spectacular advances in the structure and molecular mechanism of the pumps have been accompanied by the emergence and rapid expansion of the topic of pump malfunction, which has paralleled the rapid expansion of knowledge in the topic of Ca2+-signaling dysfunction. Most of the pump defects described so far are genetic: when they are very severe, they produce gross and global disturbances of Ca2+ homeostasis that are incompatible with cell life. However, pump defects may also be of a type that produce subtler, often tissue-specific disturbances that affect individual components of the Ca2+-controlling and/or processing machinery. They do not bring cells to immediate death but seriously compromise their normal functioning.