Identification of ubiquitinated repeats in human erythroid alpha-spectrin

The spectrin role(s) is (are) very important for the shape and the physical properties of red cells, such as deformability and resistance to mechanical stresses. Moreover a variety of spectrin diseases are known. We have previously demonstrated [Corsi, D., Galluzzi, L., Crinelli, R. & Magnani, M. (1995) J. Biol. Chem. 270, 8928-8935] that human erythroid alpha-spectrin is ubiquitinated in vitro and in vivo. In order to define the ubiquitinated repeats of this long protein and find out a possible function, we have produced recombinant peptides encompassing the alphaIII-, alphaIV-, alphaV- and EF hand domains of alpha-spectrin chain. These peptides were tested in in vitro ubiquitin conjugation assays and two regions susceptibles to ubiquitination were found. The first one, in the alphaIV-domain, includes the repeat 17 and the second one, in the alphaV-domain, includes the repeat 20 and a part of repeat 21. We also demonstrated that the susceptibility to ubiquitination of the alphaV-domain is reduced by interaction with the corresponding portion of beta-spectrin chain (betaIV-domain). Thus, at least ubiquitination of alphaV-domain is susceptible to cytoskeleton assembly and spectrin dimerization.

Posture-related changes in heteronymous recurrent inhibition from quadriceps to ankle muscles in humans

The possibility was investigated that changes in heteronymous recurrent inhibition (RI) from quadriceps (Q) to soleus (Sol) and tibialis anterior (TA) motoneurons (MNs) occur during postural tasks requiring cocontraction of Q with one of these muscles. Stimulation of the femoral nerve (FN), which elicited a Q H-reflex discharge, was used to activate Renshaw cells. The resulting inhibition of TA and Sol MNs was assessed using three test responses: (1) the rectified and averaged ongoing electromyogram (EMG) activity in TA or Sol; (2) the motor-evoked potential (MEP) elicited by cortical stimulation in these muscles; and (3) the Sol H reflex. The characteristics of the depression (appearance and increase with the conditioning reflex discharge, short central delay and long duration) are consistent with a Renshaw origin. In addition, results obtained in control experiments (no change in the EMG suppression after an ischaemic blockade of group-I afferents from the leg, time course of the FN-induced depression of the MEP similar to that of the ongoing EMG) made a significant contribution from other pathways activated by FN stimulation unlikely. Posture-related heteronymous RI from Q was compared in different postural tasks at matched levels of background EMG activity: voluntary co-contraction of Q and of the relevant ankle muscle while sitting (control situation), postural co-contraction of Q and TA (while leaning backwards during stance), or contraction of Sol with (preparation for hopping) and without (standing on tip of toes and leaning forwards during stance) associated contraction of the Q. During stance, heteronymous RI from Q was reduced to TA (but not to Sol) while leaning backwards and to Sol in preparation for hopping, but not in the other situations. Thus, RI from Q to TA or Sol was specifically decreased when a co-contraction of the Q and of the relevant muscle operating at the ankle was required to maintain bipedal stance. It is argued that this control of Renshaw cells is descending in origin and contributes to selection of the appropriate synergism in various postural tasks.

Properties of normal and mutant polypeptide fragments from the dimer self-association sites of human red cell spectrin

We have examined the properties and interactions of expressed polypeptide fragments from the N-terminus of the alpha-chain and the C-terminus of the beta-chain of human erythroid spectrin. Each polypeptide comprises one complete structural repeating unit, together with the incomplete repeat that interacts with its partner when spectrin tetramers are formed. The shared repeat thus generated is made up of two helices from the C-terminal part of the beta-chain and one helix from the N-terminus of the alpha-chain. Three mutant beta-chain fragments with amino acid substitutions in the incomplete terminal repeat were also studied. The alpha- and beta-chain fragments were both substantially monomeric, as shown by sedimentation equilibrium. Circular dichroism analysis and thermal denaturation profiles revealed that the complete repeat present in each fragment had entered the stable tertiary fold. Unexpectedly, the conformational stability of the folded beta-chain repeat was found to be grossly perturbed by the mutations, all of them well beyond its C-terminal boundary; possible explanations for this phenomenon are considered. Sedimentation equilibrium showed that in equimolar mixtures the wildtype alpha- and beta-chain peptides formed a 1:1 complex. Mixing curves, observed by circular dichroism, revealed that association was accompanied by an increase in alpha-helicity. From continuous-variation profiles an association constant in the range 1-2 x 10(6) M-1 was inferred. The association was unaffected by the apparently unstructured anionic tail of 54 residues, found at the C-terminus of the spectrin beta-chain. Of the three mutations in the beta-chain fragment, one (an Ala-->Val replacement in the A helix segment of the incomplete repeat) had a relatively small effect on the association with the alpha-chain fragment, whereas Trp-->Arg mutations in the A and in the remote B helix segments were much more deleterious. These observations are consistent with the relative severities of the haemolytic conditions associated with the mutations.

Spectrin self-association site: characterization and study of beta-spectrin mutations associated with hereditary elliptocytosis

Most of hereditary elliptocytosis (HE) cases are related to a spectrin dimer (SpD) self-association defect. The severity of haemolysis is correlated with the extent of the SpD self-association defect, which itself depends on the location of the mutation regarding the tetramerization site. This site is presumed to involve the first C helix of the alpha chain and the last two helices, A and B, of the beta chain to reconstitute a triple helical structure (A, B and C), as observed along spectrin. Using recombinant peptides, we demonstrated that the first C helix of the alpha chain and the last two helices of the beta chain alone are not sufficient to establish interactions, which only occurred when a complete triple-helical repeat was added to each partner. One adjacent repeat is necessary to stabilize the conformation of both N- and C-terminal structures directly involved in the interaction site and is sufficient to generate a binding affinity similar to that observed in the native molecule. Producing peptides carrying a betaHE mutation, we reproduced the tetramerization defect as observed in patients. Therefore, the betaW2024R and betaW2061R mutations, which replace the invariant tryptophan and a residue located in the hydrophobic core, respectively, affect alpha-beta interactions considerably. In contrast, the betaA2013V mutation, which modifies a residue located outside any presumed interacting regions, has a minor effect on the interaction.

Electron microscopy of frozen biological objects: a study using cryosectioning and cryosubstitution

Freezing of bulk biological objects was investigated by X-ray cryodiffraction. Freezing at atmospheric pressure of most microscopic biological samples gives rise to large hexagonal crystals and leads to poor structural preservation of these specimens. High-pressure freezing induces the formation of different ices (hexagonal, cubic and a high-pressure form) consisting of crystals having sizes smaller than those formed at atmospheric pressure. With both freezing methods, a cryoprotectant has to be added to the biological object to avoid the formation of ice crystals. However, special cases can be encountered: some biological objects contain large amounts of natural cryoprotectant or have a low water content. In these cases, vitrification can be achieved, especially using high-pressure freezing. Cryo-sectioning can be performed on vitrified samples, and the sections studied by electron cryomicroscopy. Images and electron diffraction patterns having a resolution better than 2 and 0.2 nm, respectively, can be obtained with such sections. Because samples containing crystalline ices cannot be cryosectioned, their structure has to be studied using cryosubstitution and resin embedding. We show that bacteria, yeast, and ciliate and marine worm elytrum have cellular compartments with an organization that has not been described by classical techniques relying on chemical fixation of the tissues. A high-pressure artefact affecting the Paramecium trichocysts is described. Such artefacts are not general; for example, we show that 70% of high-pressure frozen yeast cells survive successive high-pressure freezing and thawing steps.

Colocalization of the cyclin B homologue p56 and beta-tubulin during the cell cycle in a unicellular eucaryote dinoflagellate

We provide evidence for an unusual behavior of the cyclin B homologue, p56, in the dinoflagellate Crypthecodinium cohnii. p56, of which we previously demonstrated the presence in this original eukaryotic protist, is present all along the cell cycle progression, and is exclusively cytoplasmic as revealed after immunofluorescence labeling with anti-p56 Ab and counterstaining with Dapi. It was never found in the nucleus as is the case in higher eukaryotic cells. During mitosis, p56 was essentially associated with the mitotic apparatus: centrosomes and mitotic spindle, as shown after double immunofluorescence labeling with anti p56 and anti beta-tubulin Ab. Using high pressure freeze fixation, we clearly detected in transmission electron microscopy (TEM) the localization of p56 cyclin B homologue and beta-tubulin: single immunogold labeling demonstrated that p56 is localized along the whole cell cortex, along the cleavage furrow of anaphase to cytokinesis cells and into cytoplasmic channels passing throughout the mitotic nucleus where is located the mitotic spindle. Double immunogold labeling realized with anti-p56 and anti-beta-tubulin antibodies confirm that p56 antigens colocalize with beta-tubulin in many sites. The significance of the exclusively cytoplasmic localization of the cyclin B homologue is discussed.

Spectrin St Claude, a splicing mutation of the human alpha-spectrin gene associated with severe poikilocytic anemia

An alpha-spectrin variant with increased susceptibility to tryptic digestion, alpha(II/47), was previously observed in a child with severe, recessively inherited, poikilocytic anemia. The molecular basis of this variant, spectrin St Claude, has now been identified as a splicing mutation of the alpha-spectrin gene due to a T --> G mutation in the 3' acceptor splice site of exon 20. This polypyrimidine tract mutation creates a new acceptor splice site, AT --> AG, and leads to the production of two novel mRNAs. One mRNA contains a 12 intronic nucleotide insertion upstream of exon 20. This insertion introduces a termination codon into the reading frame and is predicted to encode a truncated protein (108 kD) that lacks the nucleation site and thus cannot be assembled in the membrane. In the other mRNA, there is in-frame skipping of exon 20, predicting a truncated (277 kD) alpha-spectrin chain. The homozygous propositus has only truncated 277 kD alpha-spectrin chains in his erythrocyte membranes. His heterozygous parents are clinically and biochemically normal. This allele was identified in 3% of asymptomatic individuals from Benin, Africa.

In situ localization of two fibrillar collagens in two compact connective tissues by immunoelectron microscopy after cryotechnical processing

Two fibrillar collagens, the worm cuticular collagen and the vertebrate Type I fish scale collagen, both organized in a compact tissue, were localized by immunogold electron microscopy in resin sections after freeze-fixation and freeze-substitution. Identification of these two fibrillar collagens failed with the use of postembedding labelling after conventional electron microscopic processing. Positive labeling of the Type I collagen was observed in sections of fish scales freeze-fixed by either slam-freezing or high-pressure freezing, freeze-substituted in acetone with or without osmium tetroxide, and embedded in LR White. The worm cuticular collagen was detected in sections of cuticle that were freeze-fixed, freeze-substituted (necessarily with osmium tetroxide added to acetone), and embedded in either LR White or Epon. It was also detected in specimens pre-fixed by aldehydes before freeze-fixation. The Type I fish scale collagen appears to be more sensitive than the fibrillar cuticular collagen of worms to the procedures employed for postembedding immunoelectron microscopy. Our results have shown that freeze-fixation and freeze-substitution preserved the antigenicity of the fibrillar collagens organized in a compact three-dimensional network, whereas immunolabeling failed after conventional electron microscopic procedures. These cryostabilization techniques appear to be of value to improve the immunolocalization of collagens.

[Cardiac sudden death in adults]

Sudden death is becoming a matter for concern as this type of accident represents an increasing proportion of deaths from cardio-vascular causes. A campaign is being launched aimed at promoting early diagnosis and appropriate action at the time of the event itself. At the same time it is necessary to get to know the target population better, especially with regard to the specific anatomical conditions which are the cause of death. For the last seven years we have been carrying out a descriptive pathological research study. The first stage took form of a three year retrospective study (1989-1991) involving 365 subjects victims of sudden death. The second part was a prospective study carried out in 1994. Heart disease emerged as the principal cause of death, something which is already well known. More interesting was the discovery that 72.3% of the subjects were completely asymptomatic despite the fact that in 85% of cases they had bi-truncal or tri-truncal lesions. The same findings emerged from the study of a subgroup of persons who had died suddenly as a result of acute stress. The data obtained are extremely homogeneous. When compared to the findings obtained from a control group of the same age who had died as the result of violence, the difference between the two populations is highly significant. Finally we should like to draw attention to the lack of epidemiological data on sudden death available in France at the present time, and this despite the fact that it is undoubtedly a public health priority. There is a need to promote both education and action in relation to this somewhat disturbing subject.

Stressful events as a trigger of sudden death: a study of 43 medico-legal autopsy cases

The reports relating emotional stress to sudden death are largely anecdotal. In addition to experimental and electrophysiological studies, an opportunity for a better understanding of possible stress-related sudden death (SSD) may be provided by medicolegal autopsies. The goal of our autopsy study was to analyze cardiovascular pathologic findings in cases of SSD and if possible identify mechanisms by which the stressful event (SE) could be the cause. Forty three cases were studied (29 males and 14 females). In all cases, the SE and the death were witnessed. The age range was 22 to 90 years in males (mean, 52) and 30 to 92 years in females (mean, 64). Death occurred in all cases without premonitory symptoms. In 20 cases, death occurred during the SE and in the other 23 cases occurred within 2 h of the event. SE included fear, 15 cases; altercation, 21 cases; sexual activity, 3 cases; police questioning or arrest, 4 cases. According to police reports, in 40 cases (90%), the victims had no previous clinical history of cardiovascular disease. At autopsy, the heart weight in males ranged from 255 to 1000 g with a mean of 517 g and in females the range was 250-700 g with a mean of 417 g. In only 3 cases, gross and microscopic examination of the heart was normal. In 2 of the remaining 40 cases the subjects died of subarachnoid hemorrhage. In 38 cases, a cardiac cause of death was found as follows: coronary heart disease, 27 cases; cardiomyopathy, 6 cases; aortic valvular stenosis, 2 cases and right ventricular dysplasia, 3 cases. A coronary artery thrombosis was found in 8 cases of sudden coronary death. Post myocardial infarction fibrosis was present in 25 cases (92%) of sudden coronary death. In conclusion, it appears from our autopsy study that SSD occurs primarily in those individuals with severe heart disease, especially coronary heart disease.

Direct visualization of a vast cortical calcium compartment in Paramecium by secondary ion mass spectrometry (SIMS) microscopy: possible involvement in exocytosis

The plasma membrane of ciliates is underlaid by a vast continuous array of membrane vesicles known as cortical alveoli. Previous work had shown that a purified fraction of these vesicles actively pumps calcium, suggesting that alveoli may constitute a calcium-storage compartment. Here we provide direct confirmation of this hypothesis using in situ visualization of total cell calcium on sections of cryofixed and cryosubstituted cells analyzed by SIMS (secondary ion mass spectrometry) microscopy a method never previously applied to protists. A narrow, continuous, Ca-emitting zone located all along the cell periphery was observed on sections including the cortex. In contrast, Na and K were evenly distributed throughout the cell. Various controls confirmed that emission was from the alveoli, in particular, the emitting zone was still seen in mutants totally lacking trichocysts, the large exocytotic organelles docked at the cell surface, indicating that they make no major direct contribution to the emission. Calcium concentration within alveoli was quantified for the first time in SIMS microscopy using an external reference and was found to be in the range of 3 to 5 mM, a value similar to that for sarcoplasmic reticulum. After massive induction of trichocyst discharge, this concentration was found to decrease by about 50%, suggesting that the alveoli are the main source of the calcium involved in exocytosis.

Triterpenoid saponins from the root of Sideroxylon foetidissimum

Two novel triterpenoid saponins named sideroxyloside B and sideroxyloside C were isolated from the root of Sideroxylon foetidissimum. On the basis of spectroscopic and chemical methods, their structures were established as 3-O-beta-D-glucopyranosyl-28-O([beta-D-apiofuranosyl-(1-->3)-beta- D- xylopyranosyl-(1-->4)-alpha-L-rhamnopyranosyl-(1-->4)] [beta-D-apiofuranosyl(1-->3)]-alpha-L-rhamnopyranosyl-(1-->2)-alph a-L- arabinopyranosyl) protobassic acid and 28-O([beta-D-xylopyranosyl-(1-->4)- alpha-L-rhamnopyranosyl-(1-->4)] [beta-D-apiofuranosyl-(1-->3)]-alpha-L- rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl) protobassic acid, respectively.

Detection of the 4977 base pair mitochondrial DNA deletion in paraffin-embedded heart tissue using the polymerase chain reaction--a new method to probe sudden cardiac death molecular mechanisms?

Detection of mitochondrial DNA deletions is performed in fresh or frozen material. At our institute, however, heart samples from subjects referred for autopsy are systematically processed for histologic examination (that is, paraffin-embedded). We were interested to know if mtDNA deletions can be detected in such material. Our data indicate that: 1) the most frequently observed deletion--the 4977 base pair deletion--can easily be detected in paraffin-embedded heart tissue; 2) this assay is sufficiently sensitive, since very low levels of the deletion can be found in normal heart tissue from young adults; and 3) buffered formalin appears to be the fixative of choice. Recent literature shows that repeated episodes of ischemia result in the accumulation of mtDNA deletions in myocardial cells. Because ischemic heart disease is a major cause of sudden cardiac death, a sensitive method for the detection of mtDNA damage in myocardial cells will be an important tool to facilitate understanding of unexpected cardiac arrest mechanisms.

[Sudden coronary death outside of hospital; an comparative autopsy study of subjects with and without previous cardiovascular diseases]

Autopsy studies of the heart of 221 subjects who suffered pre-hospital coronary sudden death were performed at the Paris Medico-Legal Institute over a period of 3 years to compare the lesions observed in subjects without known cardiovascular disease (Group A: n = 160; 72.4%) with those of subjects with known cardiovascular disease (Group B: n = 61). The proportion of men was greater in Group B (77%) that in Group A (62.5%). The average age of sudden death was the same in both groups: 65 years for men and 77 years for women. Sudden death usually occurred in the home (83%) at rest and, in one third of the cases, during sleep. Sudden death occurred in a context of severe coronary artery disease in both groups: significant triple vessel stenosis (> 75%) in 60% of subjects in both groups but thrombosis was found in only 13% of cases in Group A and 15% of cases in Group B. The mean weight of the heart was significantly greater than normal in both groups and in both sexes. In addition, the mean weight of the heart of subjects in Group B was significantly greater than that of subjects in Group A (p < 0.05). This autopsy study showed that prehospital coronary sudden death was the first sign of coronary disease in 70% of cases. Irrespective of whether the subject had known cardiovascular disease or not, sudden death occurred under similar circumstances and, in both cases, in the context of severe coronary artery disease.

Sudden out-of-hospital coronary death in patients with no previous cardiac history. An analysis of 221 patients studied at autopsy

Many epidemiological, clinical, and autopsy studies have demonstrated that the risk of sudden coronary death (SCD) is linked to the severity of coronary atherosclerotic lesions and to their thrombotic potential. However it remains unknown why some individuals manifest no clinical evidence of coronary disease until the onset of sudden death. The aim of this autopsy study has been to analyze the sociodemographic, clinical, and pathological features in case of sudden out-of-hospital coronary death where the death was the first manifestation of coronary disease. The results have been compared with those obtained from victims of SCD with known cardiac history. A total of 377 autopsies of sudden out-of-hospital cardiovascular deaths were performed at the Forensic Institute of Paris between 1989 and 1991. A total of 221 were SCD. A total of 160 of these subjects (72.4%) had no cardiac history (group A). The other 61 victims of SCD had cardiac antecedents (group B). Men account for 63% and 77% of the SCD in groups A and B respectively and are 12 years younger than women at the onset of SCD in both groups (65/77 years). Our study showed that in both groups SCD occurs in 83% of cases at home (and at rest) and in 30% of these cases while sleeping. Autopsy showed that SCD be it with or without antecedent occurs on a background of severe coronary disease with multivessels stenoses but coronary thrombosis was rarely observed (15%). SCD occurred in the context of underlying cardiomegaly.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolated myocardial fibrosis as a cause of sudden cardiac death and its possible relation to myocarditis

In performing medicolegal autopsies on sudden deaths, there occur a number of cases in which no cause of death can be found. In particular, no evidence of macroscopic cardiac abnormalities can be observed. However, extensive histological screening may reveal isolated areas of myocardial fibrosis. The five cases presented discuss the etiology of this fibrosis and its possible relation to myocarditis. The cases involve white women between the ages of 19 and 25 with no previous medical history. The weight of the heart in all five cases was normal. Macroscopic evidence of fibrosis was visible in four out of five cases. No other macroscopic abnormalities were observed. Histologically, there was evidence of scarring or interstitial fibrosis in all five cases. In four of the cases, additional screening permitted the observation of dispersed inflammatory foci consisting of lymphocytes, plasmocytes and macrophages. Two of the cases demonstrated eosinophil and neutrophil aggregates in the center of necrotic foci. No evidence of vascular inflammatory phenomena was observed in any of the five cases. According to the Dallas criteria, three of the five cases fulfill the requirements for myocarditis and one of the five cases for borderline myocarditis. The Dallas criteria, however, do not take into consideration the possible association between inflammation and myocardial fibrosis since many of the reported series of myocarditis have been from hospital autopsies or endomyocardial biopsies and have not taken into account sudden death from fibrotic sequelae of myocarditis.(ABSTRACT TRUNCATED AT 250 WORDS)