Alexander Kraev

An Ryr1I4895T mutation abolishes Ca2+ release channel function and delays development in homozygous offspring of a mutant mouse line

A heterozygous Ile4898 to Thr (I4898T) mutation in the human type 1 ryanodine receptor/Ca2+ release channel (RyR1) leads to a severe form of central core disease. We created a mouse line in which the corresponding Ryr1I4895T mutation was introduced by using a “knockin” protocol. The heterozygote does not exhibit an overt disease phenotype, but homozygous (IT/IT) mice are paralyzed and die perinatally, apparently because of asphyxia. Histological analysis shows that IT/IT mice have greatly reduced and amorphous skeletal muscle. Myotubes are small, nuclei remain central, myofibrils are disarranged, and no cross striation is obvious. Many areas indicate probable degeneration, with shortened myotubes containing central stacks of pyknotic nuclei. Other manifestations of a delay in completion of late stages of embryogenesis include growth retardation and marked delay in ossification, dermatogenesis, and cardiovascular development. Electron microscopy of IT/IT muscle demonstrates appropriate targeting and positioning of RyR1 at triad junctions and a normal organization of dihydropyridine receptor (DHPR) complexes into RyR1-associated tetrads. Functional studies carried out in cultured IT/IT myotubes show that ligand-induced and DHPR-activated RyR1 Ca2+ release is absent, although retrograde enhancement of DHPR Ca2+ conductance is retained. IT/IT mice, in which RyR1-mediated Ca2+ release is abolished without altering the formation of the junctional DHPR-RyR1 macromolecular complex, provide a valuable model for elucidation of the role of RyR1-mediated Ca2+ signaling in mammalian embryogenesis.

Ca2+ dysregulation in Ryr1I4895T/wt mice causes congenital myopathy with progressive formation of minicores, cores, and nemaline rods

Ryr1I4895T/wt (IT/+) mice express a knockin mutation corresponding to the human I4898T EC-uncoupling mutation in the type 1 ryanodine receptor/Ca2+ release channel (RyR1), which causes a severe form of central core disease (CCD). IT/+ mice exhibit a slowly progressive congenital myopathy, with neonatal respiratory stress, skeletal muscle weakness, impaired mobility, dorsal kyphosis, and hind limb paralysis. Lesions observed in myofibers from diseased mice undergo age-dependent transformation from minicores to cores and nemaline rods. Early ultrastructural abnormalities include sarcomeric misalignment, Z-line streaming, focal loss of cross-striations, and myofibrillar splitting and intermingling that may arise from defective myofibrillogenesis. However, manifestation of the disease phenotype is highly variable on a Sv129 genomic background. Quantitative RT-PCR shows an equimolar ratio of WT and mutant Ryr1 transcripts within IT/+ myofibers and total RyR1 protein expression levels are normal. We propose a unifying theory in which the cause of core formation lies in functional heterogeneity among RyR1 tetramers. Random combinations of normal and either leaky or EC-uncoupled RyR subunits would lead to spatial differences in Ca2+ transients; the resulting heterogeneity of contraction among myofibrils would lead to focal, irreversible tearing and shearing, which would, over time, enlarge to form minicores, cores, and nemaline rods. The IT/+ mouse line is proposed to be a valid model of RyR1-related congenital myopathy, offering high potential for elucidation of the pathogenesis of skeletal muscle disorders arising from impaired EC coupling.

Protocol for the Sequence Analysis of Ryanodine Receptor Subtype 1 Gene Transcripts from Human Leukocytes

Background The search for novel mutations in the ryanodine receptor subtype 1 (RYR1) gene causing malignant hyperthermia and central core disease is hampered by the fact that the gene contains 106 exons. Searching for novel mutations in complementary DNA (cDNA) requires an invasive muscle biopsy. Accordingly, an alternate source of RYR1 cDNA was sought for sequence analysis. Methods Leukocytes were isolated from human blood and used for extraction of RNA and reverse transcription of messenger RNA into cDNA. A detailed protocol was developed in which overlapping fragments of RYR1 cDNA were amplified by polymerase chain reaction in a series of steps and used for double-strand sequencing. Results The sequences of full-length leukocyte RYR1 cDNA obtained from four human blood samples were shown to be identical to the sequence of a human muscle RYR1 cDNA. The incidence of aberrant splicing was more pronounced in the blood-derived cDNAs, but this could be minimized by adequate sample preparation. Protocols to sequence alternatively spliced products were also developed. Several silent nucleotide polymorphisms were detected, and minor revisions were made to the RYR1 sequence. Conclusions Because there are no differences in RYR1 transcript structure between muscle and leukocytes, aside from those that may be ascribed to RNA splicing aberrations during processing, leukocytes seem to be an adequate substitute tissue for screening the RYR1 gene for previously undiscovered mutations in families with malignant hyperthermia or central core disease.

Ryanodine receptor type 1 gene mutations found in the Canadian malignant hyperthermia population

PurposeMalignant hyperthermia (MH) is an autosomal dominant pharmacogenetic disorder that is manifested on exposure of susceptible individuals to halogenated anesthetics or succinylcholine. Since MH is associated primarily with mutations in the ryanodine receptor type 1 (RYR1) gene, the purpose of this study was to determine the distribution and frequency of MH causative RyR1 mutations in the Canadian MH susceptible (MHS) population.MethodsIn this study, we screened a representative cohort of 36 unrelated Canadian MHS individuals for RYR1 mutations by sequencing complete RYR1 transcripts and selected regions of CACNA1S transcripts. We then analyzed the correlation between caffeine-halothane contracture test (CHCT) results and RYR1 genotypes within MH families.ResultsEighty-six percent of patients had at least one RyR1 mutation (31 out of 36), five of which were unrelated individuals who were double-variant carriers. Fifteen of the 27 mutations identified in RYR1 were novel. Eight novel mutations, involving highly conserved amino acid residues, were predicted to be causal. Two of the mutations co-segregated with the MHS phenotype within two large independent families (a total of 79 individuals). Fourteen percent of MHS individuals (five out of 36) carried neither RYR1 nor known CACNA1S mutations.ConclusionsThe distribution and frequency of MH causative RyR1 mutations in the Canadian MHS population are close to those of European MHS populations. Novel mutations described in this study will contribute to the worldwide pool of MH-associated mutations in the RYR1 gene, ultimately increasing the value of MH genetic diagnostic testing.RésuméObjectifL’hyperthermie maligne (HM) est une maladie pharmacogénétique héréditaire dominante autosomique qui se manifeste lors de l’exposition des personnes susceptibles à des anesthésiques halogénés ou à la succinylcholine. Étant donné que l’HM est principalement associée aux mutations au niveau du gène des récepteurs de ryanodine de type 1 (RYR1), l’objectif de cette étude était de déterminer la distribution et la fréquence des mutations RyR1 causant une HM chez la population canadienne susceptible à l’HM (SHM).MéthodeDans cette étude, nous avons examiné une cohorte représentative de 36 personnes canadiennes SHM sans liens familiaux pour identifier les mutations RYR1 en séquençant des transcrits complets de RYR1 et des régions choisies de transcrits de CACNA1S. Nous avons ensuite analysé la corrélation entre les résultats de l’étude de la contractilité de la cellule musculaire en présence de caféine et d’halothane (test CHCT) et les génotypes RYR1 au sein des familles d’HM.RésultatsQuatre-vingt-six pour cent (31 sur 36) des patients ont manifesté au moins une mutation RyR1, dont cinq sans liens familiaux étaient porteurs de la double variante. Quinze des 27 mutations identifiées sur le RYR1 étaient nouvelles. Huit mutations nouvelles, y compris des acides aminés bien conservés, ont été anticipées comme étant causales. Deux des mutations se sont co-ségrégées avec le phénotype SHM dans deux vastes familles indépendantes (au total 79 personnes). Quatorze pour cent des personnes SHM (cinq sur les 36) n’étaient porteuses ni des mutations de RYR1 ni de mutations connues de CACNA1S.ConclusionLa distribution et la fréquence de mutations de RyR1 causatives de HM dans la population canadienne SHM sont semblables à celles de populations européennes SHM. Les nouvelles mutations décrites dans cette étude s’ajouteront au fonds mondial de mutations associées à la HM dans le gène RYR1, ce qui contribuera à augmenter la valeur du dépistage diagnostique génétique de l’HM.

CASQ1 gene is an unlikely candidate for malignant hyperthermia susceptibility in the North American population.

Background:Malignant hyperthermia (MH, MIM# 145600) is a complex pharmacogenetic disorder that is manifested in predisposed individuals as a potentially lethal reaction to volatile anesthetics and depolarizing muscle relaxants. Studies of CASQ1-null mice have shown that CASQ1, encoding calsequestrin 1, the major Ca2+ binding protein in the lumen of the sarcoplasmic reticulum, is a candidate gene for MH in mice. The aim of this study was to establish whether the CASQ1 gene is associated with MH in the North American population. Methods:The entire coding region of CASQ1 in 75 unrelated patients diagnosed by caffeine-halothane contracture test as MH susceptible (MHS) was analyzed by DNA sequencing. Subsequently, three groups of unrelated individuals (130 MHS, 100 MH negative, and 192 normal controls) were genotyped for a variant that was identified by sequencing. Levels of CASQ1 expression in the muscle from unrelated MHS and MH negative individuals were estimated by Western blotting. Results:Screening of the entire coding sequence of the CASQ1 gene in 75 MHS patients revealed a single variant c.260T > C (p.Met87Thr) in exon 1. This variant is unlikely to be pathogenic, because its allele frequency in the MHS group was not significantly different from that of controls. There was also no difference in calsequestrin 1 protein levels between muscle samples from MHS and controls, including those carrying the p.Met87Thr variant. Conclusions:This study revealed a low level of protein coding sequence variability within the human CASQ1 gene, indicating that CASQ1 is not a major MHS locus in the North American population.

Detection of a Novel Ryanodine Receptor Subtype 1 Mutation (R328W) in a Malignant Hyperthermia Family by Sequencing of a Leukocyte Transcript

Background To determine whether malignant hyperthermia (MH) susceptibility in a Canadian pedigree is associated with a mutation in the ryanodine receptor subtype 1 (RYR1) gene, the complete RYR1 transcript obtained from the leukocytes of one MH-susceptible family member was sequenced, using a newly developed protocol. Methods RNA was extracted from leukocytes and converted into complementary DNA. Overlapping fragments of RYR1 complementary DNA were amplified by the polymerase chain reaction and used for double-strand sequencing to find a single mutation likely to be causal of MH susceptibility. Inheritance of the mutation in the family was studied by restriction endonuclease analysis and/or sequencing of genomic DNA and compared to available caffeine halothane contracture test data. The mutation was introduced into rabbit RYR1 complementary DNA, the complementary DNA was expressed in human embryonic kidney line 293 cells, and Ca2+ release by the mutant Ca2+ release channel was measured following the addition of caffeine and halothane. Results A novel arginine 328 to tryptophan mutation in RYR1 was detected by direct sequencing of the RYR1 transcript from leukocytes of one MH-susceptible individual. A causal role for this mutation in MH is indicated by cosegregation of the mutation with the MH-susceptible phenotype within the family and by the demonstration that the mutant channel has increased sensitivity to both caffeine and halothane. Conclusions The feasibility of using complete RYR1 transcripts from leukocytes for sequence analysis offers an efficient and noninvasive method for scanning RYR1 for novel mutations.

Novel excitation-contraction uncoupled RYR1 mutations in patients with central core disease.

Central core disease, one of the most common congenital myopathies in humans, has been linked to mutations in the RYR1 gene encoding the Ca(2+) release channel of the sarcoplasmic reticulum (RyR1). Functional analyses showed that disease-associated RYR1 mutations led to impairment of skeletal muscle Ca(2+) homeostasis; however, thorough understanding of the molecular mechanisms underlying central core disease and other RyR1-related conditions is still lacking. We screened by sequencing the complete RYR1 transcripts in ten unrelated patients with central core disease and identified five novel, p.M4640R, p.L4647P, p.F4808L, p.D4918N and p.F4941C, and four recurrent mutations. Four of the novel mutations involved amino acid residues that were positioned within putative transmembrane segments of the RyR1. The pathogenic character of the identified mutations was demonstrated by bioinformatic analyses and by the in vitro functional studies in HEK293 cells and RYR1-null (dyspedic) myotubes. Characterization of Ca(2+) channel properties of RyR1s carrying one recurrent and two novel mutations upholds the view that diminished intracellular Ca(2+) release caused by impaired Ca(2+) channel gating and/or Ca(2+) permeability is an important component of central core disease etiology. This study expands the list of functionally characterized disease-associated RyR1 mutations, increasing the value of genetic diagnosis for RyR1-related disorders.

Parallel universes of Black Six biology

Creation of lethal and synthetic lethal mutations in an experimental organism is a cornerstone of genetic dissection of gene function, and is related to the concept of an essential gene. Common inbred mouse strains carry background mutations, which can act as genetic modifiers, interfering with the assignment of gene essentiality. The inbred strain C57BL/6J, commonly known as “Black Six”, stands out, as it carries a spontaneous homozygous deletion in the nicotinamide nucleotide transhydrogenase (Nnt) gene [GenBank: AH009385.2], resulting in impairment of steroidogenic mitochondria of the adrenal gland, and a multitude of indirect modifier effects, coming from alteration of glucocorticoid-regulated processes. Over time, the popular strain has been used, by means of gene targeting technology, to assign “essential” and “redundant” qualifiers to numerous genes, thus creating an internally consistent “parallel universe” of knowledge. It is unrealistic to suggest phasing-out of this strain, given the scope of shared resources built around it, however, continuing on the road of “strain-unawareness” will result in profound waste of effort, particularly where translational research is concerned. The review analyzes the historical roots of this phenomenon and proposes that building of “parallel universes” should be urgently made visible to a critical reader by obligatory use of unambiguous and persistent tags in publications and databases, such as hypertext links, pointing to a vendor’s strain description web page, or to a digital object identifier (d.o.i.) of the original publication, so that any research done exclusively in C57BL/6J, could be easily identified.ReviewersThis article was reviewed by Dr. Neil Smalheiser and Dr. Miguel Andrade-Navarro.

Insertional mutagenesis in PLNR9C transgenic mouse: a case report and a review of the literature on cardiac-specific transgenic expression

A mouse line with heterozygous transgenic expression of phospholamban carrying a substitution of cysteine for arginine 9 (PLNR9C) under the control of α-myosin heavy chain (αMHC) promoter features dilated cardiomyopathy, heart failure and premature death. In this line the transgenic array of 13 PLNR9C expression cassettes, arranged in a head-to-tail tandem orientation, has integrated into the homologous genomic site, the bi-directional promoter of the αMHC (Myh6) gene and the gene for the regulatory non-coding RNA Myheart (Mhrt), both of which are involved in the execution of the α/β MHC switch during cardiac development and pathology. PLNR9C overexpression is evident at the age of 1 month but declines dramatically along with a less pronounced concomitant decline of the resident PLN expression, until the animals die. Expression of the non-coding RNA Mhrt in PLNR9C mice also exhibits a profound deregulation, despite the presence of the second, intact allele. Hence the mouse strain does not faithfully model a human PLNR9C heterozygote, wherein both the mutant and the wildtype PLN alleles have, in all likelihood, the same temporal expression profile. The intricate regulatory circuit of the α/β MHC switch, involving the non-coding RNA Mhrt, was described in detail only recently, and since publications about αMHC-driven transgenes rarely contain the definition of the transgene integration site or temporal expression profile, it is suggested that some of the pathological phenomena attributed to expression of αMHC-driven transgenes may have an alternative explanation.