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Background Cardiac light chain amyloidosis (AL-CA) patients often die within three months of starting chemotherapy. Chemotherapy for non-immunoglobulin M gammopathy with AL-CA frequently includes bortezomib (Bor), cyclophosphamide (Cy), and dexamethasone (D). We previously reported that NT-ProBNP levels can double within 24h of dexamethasone administration, suggesting a deleterious impact on cardiac function. In this study, we evaluate the role of dexamethasone in early cardiovascular mortality during treatment. Methods and findings We retrospectively assessed 100 de novo cardiac AL patients (62% male, mean age 68 years) treated at our institute between 2009 and 2018 following three chemotherapy regimens: CyBorDComb (all initiated on day 1; 34 patients), DCyBorSeq (D, day 1; Cy, day 8; Bor, day 15; 17 patients), and CyBorDSeq (Cy, day 1; Bor, day 8; D, day 15; 49 patients). The primary endpoint was cardiovascular mortality and cardiac transplantation at days 22 and 455. At day 22, mortality was 20.6% with CyBorDComb, 23.5% with DCyBorSeq, and 0% with CyBorDSeq (p = 0.003). At day 455, mortality was not significantly different between regimens (p = 0.195). Acute toxicity of dexamethasone was evaluated on myocardial function using a rat model of isolated perfused heart. Administration of dexamethasone induced a decrease in left ventricular myocardium contractility and relaxation (p Conclusion Delaying dexamethasone during the first chemotherapy cycle reduces the number of early deaths without extending survival. It is clear that dexamethasone is beneficial in the long-term treatment of patients with AL-CA. However, the initial introduction of dexamethasone during treatment is critical, but may be associated with early cardiac deaths in severe CA. Thus, it is important to consider the dosage and timing of dexamethasone introduction on a patient-severity basis. The impact of dexamethasone in the treatment of AL-CA needs further investigation.

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Introduction Myofibrillar myopathy (MFM) is a group of severe cytokeletal proteins known to be caused by mutations in genes encoding. Among the myofibrillar proteins that are accumulated within the muscle fibers of affected patients, they appear to be responsible for the structural integrity of striated muscle. Mutations in the gene lead not only to skeletal muscle myopathies but also to cardiomyopathies, however the cardiac pathological consequences caused by them remain poorly understood. Objective The objective of this work is to examine the effects of MFM-induced mutations in the structural organization of cardiomyocytes derived from human induced pluripotent stem cells (hiPSCs) as identified by troponinT immunostaining, and rat neonatal cardiomyocytes. Method We propose an in vitro cardiac disease-based cellular model based on adeno-associated virus (AAV)-mediated transduction of wild-type (WT) and mutated desmin in fusion with a c-myc tag to distinguish between endogenous and transgenic desmin proteins. Results Our preliminary results demonstrated that cardiomyocytes were successfully transduced by AAV vectors and expressed exogenous WT desmin as revealed by c-myc immunostaining. For better recapitulating the in vivo anisotropic cardiomyocyte organization, we have developed micro-patterned culture plates made by microcontact printing where thin strips of gelatin have been deposited on top of glass. Culture of both hiPSC-derived and rat neonatal cardiomyocytes on this system improved their sarcomere alignment. The analysis based on immunostaining of protein-markers to examine structural organization in AAV-transduced cardiomyocytes is in progress. Conclusions Our results indicate that the proposed in vitro model is suitable for the study of the structural defects of desmin-mutated cardiomyocytes.

Ankyrins, the adapters of the spectrin skeleton, are involved in local accumulation and stabilization of integral proteins to the appropriate membrane domains. In striated muscle, tissue-dependent alternative splicing generates unique Ank3 gene products (ankyrins-G); they share the Obscurin/Titin-Binding-related Domain (OTBD), a muscle-specific insert of the C-terminal domain which is highly conserved among ankyrin genes, and binds obscurin and titin to Ank1 gene products. We previously proposed that OTBD sequences constitute a novel domain of protein-protein interactions which confers ankyrins with specific cellular functions in muscle. Here we searched for muscle proteins binding to ankyrin-G OTBD by yeast two hybrid assay, and we found plectin and filamin C, two organizing elements of the cytoskeleton with essential roles in myogenesis, muscle cell cytoarchitecture, and muscle disease. The three proteins coimmunoprecipitate from skeletal muscle extracts and colocalize at costameres in adult muscle fibers. During in vitro myogenesis, muscle ankyrins-G are first expressed in postmitotic myocytes undergoing fusion to myotubes. In western blots of subcellular fractions from C2C12 cells, the majority of muscle ankyrins-G appear associated with membrane compartments. Occasional but not extensive co-localization at nascent costameres suggested that ankyrin-G interactions with plectin and filamin C are not involved in costamere assembly; they would rather reinforce stability and/or modulate molecular interactions in sarcolemma microdomains by establishing novel links between muscle-specific ankyrins-G and the two costameric dystrophin-associated glycoprotein and integrin-based protein complexes. These results report the first protein-protein interactions involving the ankyrin-G OTBD domain and support the hypothesis that OTBD sequences confer ankyrins with a gain of function in vertebrates, bringing further consolidation and resilience of the linkage between sarcomeres and sarcolemma.

Voltage-dependant sodium channels at the axon initial segment and nodes of Ranvier colocalize with the nodal isoforms of ankyrinG (AnkG node). Using fusion proteins derived from the intracellular regions of the Nav1.2a subunit and the Ank repeat domain of AnkG node, we mapped a major interaction site in the intracellular loop separating α subunit domains I-II. This 57-amino acid region binds the Ank repeat region with a K D value of 69 nm. We identified another site in intracellular loop III-IV, and we mapped both Nav1.2a binding sites on the ankyrin repeat domain to the region encompassing repeats 12–22. The ankyrin repeat domain did not bind the β1 and β2 subunit cytoplasmic regions. We showed that in cultured embryonic motoneurons, expression of the β2 subunit is not necessary for the colocalization of AnkG node with functional sodium channels at the axon initial segment. Antibodies directed against the β1subunit intracellular region, α subunit loop III-IV, and AnkG node could not co-immunoprecipitate AnkGnode and sodium channels from Triton X-100 solubilisates of rat brain synaptosomes. Co-immunoprecipitation of sodium channel α subunit and of the 270- and 480-kDa AnkG node isoforms was obtained when solubilization conditions that maximize membrane protein extraction were used. However, we could not find conditions that allowed for co-immunoprecipitation of ankyrin with the sodium channel β1 subunit.

Ankyrins are a multi-gene family of peripheral proteins that link ion channels and cell adhesion molecules to the spectrin-based skeleton in specialized membrane domains. In the mammalian skeletal myofiber, ankyrins were immunolocalized in several membrane domains, namely the costameres, the postsynaptic membrane and the triads. Ank1 and Ank3 transcripts were previously detected in skeletal muscle by northern blot analysis. However, the ankyrin isoforms associated with these domains were not identified, with the exception of an unconventional Ank1 gene product that was recently localized at discrete sites of the sarcoplasmic reticulum. Here we study the expression and subcellular distribution of the Ank3 gene products, the ankyrinsG, in the rat skeletal muscle fiber. Northern blot analysis of rat skeletal muscle mRNAs using domain-specific Ank3 cDNA probes revealed two transcripts of 8.0 kb and 5.6 kb containing the spectrin-binding and C-terminal, but not the serine-rich, domains. Reverse transcriptase PCR analysis of rat skeletal muscle total RNA confirmed the presence of Ank3 transcripts that lacked the serine-rich and tail domains, a major insert of 7813 bp at the junction of the spectrin-binding and C-terminal domains that was previously identified in brain Ank3 transcripts. Immunoblot analysis of total skeletal muscle homogenates using ankyrinG-specific antibodies revealed one major 100 kDa ankyrinG polypeptide. Immunofluorescence labeling of rat diaphragm cryosections showed that ankyrin(s)G are selectively associated with (1) the depths of the postsynaptic membrane folds, where the voltage-dependent sodium channel and N-CAM accumulate, and (2) the sarcoplasmic reticulum, as confirmed by codistribution with the sarcoplasmic reticulum Ca2+-ATPase (SERCA 1). At variance with ankyrin(s)G, ankyrin(s)R (ank1 gene products) accumulate at the sarcolemma and at sarcoplasmic structures, in register with A-bands. Both ankyrin isoforms codistributed over Z-lines and at the postsynaptic membrane. These data extend the notion that ankyrins are differentially localized within myofibers, and point to a role of the ankyrinG family in the organization of the sarcoplasmic reticulum and the postsynaptic membrane.

AlphaII-spectrin, a basic component of the spectrin-based scaffold which organizes and stabilizes membrane microdomains in most animal cells, has been recently implicated in cell adherence and actin dynamics. Here we investigated the contribution of αΙΙ-spectrin to neuritogenesis, a highly complex cellular process which requires continuous actin cytoskeleton remodeling and cross-talk between extracellular cues and their cell surface receptors, including cell adhesion molecules. Using RNA interference-mediated gene silencing to down-regulate αΙΙ-spectrin expression in human neuroblastoma SH-SY5Y cells, we observed major changes in neurite morphology and cell shape: (1) reduced mean length and a higher number of neurites per cell; occasional long neurites were thinner and displayed abnormal adhesiveness during cell migration resulting in frequent breaks; similar persisting adhesiveness and breaks were also observed in trailing edges of cell bodies; (2) irregular polygonal cell shape in parallel with loss of cortical F-actin from neuronal cell bodies; (3) reduction in protein levels of αΙ- and βΙ-spectrins, but not βΙΙ-spectrin (4) decreased global expression of adhesion molecule L1 and spectrin-binding adapter ankyrin-B, which links L1 to the plasma membrane. Remarkably, αΙΙ-spectrin depletion affected L1 – but not NCAM – cell surface expression, and L1 clustering at growth cones. This study demonstrates that αΙΙ-spectrin is implicated in normal morphology and adhesive properties of neuron cell bodies and neurites, and in cell surface expression and organization of adhesion molecule L1.

We have characterized a new ankyrin gene, expressed in brain and other tissues, that is subject to extensive tissue-specific alternative mRNA processing. The full-length polypeptide has a molecular mass of 480 kDa and includes a predicted globular head domain, with membrane- and spectrin-binding activities, as well as an extended "tail" domain. We term this gene ankyrinG based on its giant size and general expression. Two brain-specific isoforms of 480 kDa and 270 kDa were identified that contain a unique stretch of sequence highly enriched in serine and threonine residues immediately following the globular head domain. Antibodies against the serine-rich domain and spectrin-binding domain revealed labeling of nodes of Ranvier and axonal initial segments. Ankyrin-binding proteins also known to be localized in these specialized membrane domains include the voltage-dependent sodium channel, the sodium/potassium ATPase, sodium/calcium exchanger, and members of the neurofascin/L1 family of cell adhesion molecules. The neural-specific ankyrinG polypeptides are candidates to participate in maintenance/targeting of ion channels and cell adhesion molecules to nodes of Ranvier and axonal initial segments.

440-kD ankyrinB is an alternatively spliced variant of 220-kD ankyrinB, with a predicted 220-kD sequence inserted between the membrane/spectrin binding domains and COOH-terminal domain (Kunimoto, M., E. Otto, and V. Bennett. 1991. J. Cell Biol. 236:1372-1379). This paper presents the sequence of 2085 amino acids comprising the alternatively spliced portion of 440-kD ankyrinB, and provides evidence that much of the inserted sequence has the configuration of an extended random coil. Notable features of the inserted sequence include a hydrophilicity profile that contains few hydrophobic regions, and 220 predicted sites for phosphorylation by protein kinases (casein kinase 2, protein kinase C, and proline-directed protein kinase). Secondary structure and folding of the inserted amino acid residues were deduced from properties of recombinant polypeptides. Frictional ratios of 1.9-2.4 were calculated from Stokes radii and sedimentation coefficients, for polypeptides comprising 70% of the inserted sequence, indicating a highly asymmetric shape. Circular dichroism spectra of these polypeptides indicate a nonglobular structure with negligible alpha-helix or beta sheet folding. These results suggest a ball-and-chain model for 440-kD ankyrinB with a membrane-associated globular head domain and an extended filamentous tail domain encoded by the inserted sequence. Immunofluorescence and immunoblot studies of developing neonatal rat optic nerve indicate that 440-kD ankyrinB is selectively targeted to premyelinated axons, and that 440-kD ankyrinB disappears from these axons coincident with myelination. Hypomyelinated nerve tracts of the myelin-deficient Shiverer mice exhibit elevated levels of 440-kD ankyrinB. 440-kD ankyrinB thus is a specific component of unmyelinated axons and expression of 440-kD ankyrinB may be downregulated as a consequence of myelination.

Accurate neurotransmission between motor nerve and muscle fibres at the vertebrate cholinergic neuromuscular junction (NMJ) depends on the differentiation of highly specialised structures both pre- and postsynaptically. The accumulation of nicotinic acetylcholine receptors (AChRs) and voltage-gated sodium channels represents the hallmark of postsynaptic membrane differentiation. Several synaptic organising proteins are required for the aggregation of postsynaptic AChRs. The muscle-specific receptor tyrosine kinase (MuSK) provides a structural scaffold necessary to initiate aggregates of postsynaptic molecules. Agrin – a nerve-derived extracellular matrix glycoprotein – is required for AChR clustering probably by activating MuSK activity. Rapsyn – the AChR-associated peripheral protein acting downstream of agrin–MuSK signalling – is essential for AChR clustering. These proteins, together with a wealth of other components of the synapse, cooperate in multiple ways to play both structural and signalling roles in synaptic differentiation. Synaptopathies of the NMJ result from mutations in several key players of synaptic differentiation. Key Concepts: Efficient communication between neurons or between neurons and their targets requires the enrichment of synaptic proteins, in particular, ligand-gated ion channels at postsynaptic sites. The NMJ represents a particularly striking example of accumulation of nicotinic acetylcholine receptors in the postsynaptic membrane and is an ideal model to study receptor clustering. Formation and maintenance of the postsynaptic membrane is a complex mechanism involving synaptic organising molecules derived both from nerve and muscle. The muscle tyrosine kinase, MuSK, is the master organiser of the NMJ capable to initiate clustering of postsynaptic components, even in the absence of neuronal cues. Mutations in several components of the postsynaptic membrane (not only in AChR subunits genes but also in agrin, ColQ, DOK-7, laminin, MuSK, rapsyn, etc.) result in severe dysfunction of the NMJ: the congenital myasthenic syndromes. Keywords: acetylcholinesterase; agrin; congenital myasthenic syndromes; nicotinic acetylcholine receptor; voltage-sensitive sodium channel; rapsyn; synapse

Two variants of ankyrin have been distinguished in rat brain tissue using antibodies: a broadly distributed isoform (ankyrinB) that represents the major form of ankyrin in brain and another isoform with a restricted distribution (ankyrinR) that shares epitopes with erythrocyte ankyrin. The ankyrinR isoform was localized by immunofluorescence in cryosections of rat spinal cord gray matter and myelinated central and peripheral nerves to: (a) perikarya and initial axonal segments of neuron cells, (b) nodes of Ranvier of myelinated nerve with no detectable labeling in other areas of the myelinated axons, and (c) the axolemma of unmyelinated axons. Immunogold EM on ultrathin cryosections of myelinated nerve showed that ankyrinR was localized on the cytoplasmic face of the axolemma and was restricted to the nodal and, in some cases, paranodal area. The major isoform of ankyrin in brain (ankyrinB) displayed a broad distribution on glial and neuronal cells of the gray matter and a mainly glial distribution in central myelinated axons with no significant labeling on the axolemma. These results show that (a) ankyrin isoforms display a differential distribution on glial and neuronal cells of the nervous tissue; (b) an isoform of ankyrin codistributes with the voltage-dependent sodium channel in both myelinated and unmyelinated nerve fibers. Ankyrin interacts in vitro with the voltage-dependent sodium channel (Srinivasan, Y., L. Elmer, J. Davis, V. Bennett, and K. Angelides. 1988. Nature (Lond.). 333:177-180). A specific interaction of an isoform of ankyrin with the sodium channel thus may play an important role in the morphogenesis and/or maintenance of the node of Ranvier.

Ankyrins are versatile adaptor proteins that join the spectrin-based cytoskeleton to transmembrane proteins, and have roles in organizing the microstructure of cell membranes. Molecular diversity of ankyrins in mammals arises from extensive alternative splicing of the products of three genes. There has been no systematic analysis of the diversity of expression of ankyrins-G, the widely expressed Ank3 gene products, in a complex tissue. We previously described Ank(G107), the first muscle-specific ankyrin-G. Here, we combined cDNA and database analyses to gain novel insight into the ankyrins-G of skeletal muscle. We find: (i) that Ank3 is composed of at least 53 exons, many of which are subject to tissue-specific splicing; (ii) five novel full-length cDNAs encoding two canonical (Ank(G197), Ank(G217)) and three small isoforms (Ank(G109), Ank(G128), Ank(G130)) bring to six the number of ankyrins-G expressed in skeletal muscle; (iii) a 76-residue insert in the C-terminal domain is a 'signature' for muscle ankyrins; (iv) variably spliced sequences of 17/18 and 195 residues increase diversity in the C-terminal domains. Comparison of endogenous ankyrins-G with in vitro translated cDNAs revealed that small ankyrins account for the majority of the immunoreactivity for ankyrin-G in soleus muscle. The small ankyrins, when expressed in vivo in the rat muscle, are all targeted to sarcolemmal costameres. Our results demonstrate the tissue-dependent alternative splicing of Ank3 in skeletal muscle and point to novel functions of small ankyrins-G in organizing microdomains of the plasma membrane.

Voltage-dependant sodium channels at the axon initial segment and nodes of Ranvier colocalize with the nodal isoforms of ankyrin(G) (Ank(G) node). Using fusion proteins derived from the intracellular regions of the Nav1.2a subunit and the Ank repeat domain of Ank(G) node, we mapped a major interaction site in the intracellular loop separating alpha subunit domains I-II. This 57-amino acid region binds the Ank repeat region with a K(D) value of 69 nm. We identified another site in intracellular loop III-IV, and we mapped both Nav1.2a binding sites on the ankyrin repeat domain to the region encompassing repeats 12-22. The ankyrin repeat domain did not bind the beta(1) and beta(2) subunit cytoplasmic regions. We showed that in cultured embryonic motoneurons, expression of the beta(2) subunit is not necessary for the colocalization of Ank(G) node with functional sodium channels at the axon initial segment. Antibodies directed against the beta(1) subunit intracellular region, alpha subunit loop III-IV, and Ank(G) node could not co-immunoprecipitate Ank(G) node and sodium channels from Triton X-100 solubilisates of rat brain synaptosomes. Co-immunoprecipitation of sodium channel alpha subunit and of the 270- and 480-kDa AnkG node isoforms was obtained when solubilization conditions that maximize membrane protein extraction were used. However, we could not find conditions that allowed for co-immunoprecipitation of ankyrin with the sodium channel beta(1) subunit.

International audience; We previously showed that alternatively spliced ankyrins-G, the Ank3 gene products, are expressed in skeletal muscle and localize to the postsynaptic folds and to the sarcoplasmic reticulum. Here we report the molecular cloning, tissue expression, and subcellular targeting of Ank(G107), a novel ankyrin-G from rat skeletal muscle. Ank(G107) lacks the entire ANK repeat domain and contains a 76-residue sequence near the COOH terminus. This sequence shares homology with COOH-terminal sequences of ankyrins-R and ankyrins-B, including the muscle-specific skAnk1. Despite widespread tissue expression of Ank3, the 76-residue sequence is predominantly detected in transcripts of skeletal muscle and heart, including both major 8- and 5.6-kb mRNAs of skeletal muscle. In 15-day-old rat skeletal muscle, antibodies against the 76-residue sequence localized to the sarcolemma and to the postsynaptic membrane and cross-reacted with three endogenous ankyrins-G, including one 130-kDa polypeptide that comigrated with in vitro translated Ank(G107). In adult muscle, these polypeptides appeared significantly decreased, and immunofluorescence labeling was no more detectable. Green fluorescent protein-tagged Ank(G107) transfected in primary cultures of rat myotubes was targeted to the plasma membrane. Deletion of the 76-residue insert resulted in additional cytoplasmic labeling suggestive of a reduced stability of Ank(G107) at the membrane. Recruitment of the COOH-terminal domain to the membrane was much less efficient but still possible only in the presence of the 76-residue insert. We conclude that the 76-residue sequence contributes to the localization and is essential to the stabilization of Ank(G107) at the membrane. These results suggest that tissue-dependent and developmentally regulated alternative processing of ankyrins generates isoforms with distinct sequences, potentially involved in specific protein-protein interactions during differentiation of the sarcolemma and, in particular, of the postsynaptic membrane.

It is established that variations in the structure and activities of betaI spectrin are mediated by differential mRNA splicing. The two betaI spectrin splice forms so far identified have either long or short C-terminal regions. Are analogous mechanisms likely to mediate regulation of betaII spectrins? Thus far, only a long form of betaII spectrin is reported in the literature. Five human expressed sequence tags indicated the existence of a short splice variant of betaII spectrin. The occurrence and DNA sequence of the short C-terminal variant was confirmed by analysis of human and rat cDNA. The novel variant lacks a pleckstrin homology domain, and has 28 C-terminal residues not present in the previously recognized longer form. Transcripts of the short C-terminal variant (7.5 and 7. 0 kb) were most abundant in tissues originating from muscle and nervous system. Antibodies raised to a unique sequence of short C-terminal variant recognized 240 kDa polypeptides in cardiac and skeletal muscle and in nervous tissue; in cerebellum and forebrain, additional 270 kDa polypeptides were detected. In rat heart and skeletal muscle, both long and short C-terminal forms of betaII spectrin localized in the region of the Z line. The central region of the sarcomere, coincident with the M line, was selectively labeled with antibodies to the short C-terminal form. In cerebellum, the short form was not detectable in parallel fibers, structures in which the long form was readily detected. In cultured cerebellar granule neurons, the long form was dominant in neurites, with the short form being most abundant in cell bodies. In vitro, the short form was found to lack the binding activity for the axonal protein fodaxin, which characterizes the C-terminal region of the long form. Subcellular fractionation of brain revealed that the short form was scarcely detectable in post-synaptic density preparations, in which the long form was readily detected. We conclude that variation in the structure of the C-terminal regions of betaII spectrin isoforms correlates with their differential intracellular targeting.

Many aspects of the organization of the electromotor synapse of electric fish resemble the nerve-muscle junction. In particular, the postsynaptic membrane in both systems share most of their proteins. As a remarquable source of cholinergic synapses, the Torpedo electrocyte model has served to identify the most important components involved in synaptic transmission such as the nicotinic acetylcholine receptor and the enzyme acetylcholinesterase, as well as proteins associated with the subsynaptic cytoskeleton and the extracellular matrix involved in the assembly of the postsynaptic membrane, namely the 43-kDa protein-rapsyn, the dystrophin/ utrophin complex, agrin, and others. This review encompasses some representative experiments that helped to clarify essential aspects of the supramolecular organization and assembly of the postsyn- aptic apparatus of cholinergic synapses. Microsc. Res. Tech. 49:73- 83, 2000. © 2000 Wiley-Liss, Inc.

Isoforms of ankyrin (ankyrinsR) immunologically related to erythrocyte ankyrin (ankyrinRo) are associated with distinct neuronal plasma membrane domains of functional importance, such as cell bodies and dendrites, axonal hillock and initial segments, and nodes of Ranvier. AnkyrinRo is expressed in brain, and accounts for at least one of the ankyrinR isoforms. Another ankyrin isoform of brain, ankyrinB, is encoded by a distinct gene and is immunologically distinct from ankyrinsR. Mutant mice with normoblastosis (nb/nb) constitute the first described genetic model of ankyrin deficiency: they display a severe hemolytic anemia due to a significantly reduced expression of the ankyrinRo gene in reticulocytes as well as brain (Peters L. L., C. S. Birkenmeier, R. T. Bronson, R. A. White, S. E. Lux, E. Otto, V. Bennett, A. Higgins, and J. E. Barker. 1991. J. Cell Biol. 114:1233-1241). In the present report, we distinguish between ankyrinRo and other ankyrinR isoforms using immunoblot analysis and immunofluorescence localization of ankyrinsR throughout the nervous system (forebrain, cerebellum, brain stem, spinal cord, and sciatic nerve) of nb/nb and normal mice. This is the first immunocytochemical characterization of the neurological component of the nb mutation and shows the following. (a) The isoform of ankyrin at the nodes of Ranvier and initial axonal segments is present in the nb/nb mice and does not cross-react with an ankyrinRo-specific antibody; this isoform, therefore, is distinct from both ankyrin isoforms identified in brain, ankyrinRo and ankyrinB, and is probably the product of a distinct gene and a unique component of the specialized membrane skeleton associated with nodes of Ranvier. (b) AnkyrinRo missing from nb/nb mice is selectively associated with neuronal cell bodies and dendrites, excluded from myelinated axons, and displays a selective pattern of expression in the nervous system whereby expression is almost ubiquitous in neurons of the cerebellum (Purkinje and granule cells) and spinal cord, and restricted to a very minor subset of neurons in hippocampus and neocortex of forebrain.

Publisher Summary Spectrin is a flexible rod-shaped molecule, comprising two subunits, aligned side-to-side to form hetero-dimers and head-to-head into tetramers that are capable of cross-linking actin, with binding sites, for actin on both ends. Two classes of protein interactions have been identified as an essential for the assembly of spectrin tetramers into a membrane-associated network; linkage of spectrin to the membrane and association of multiple spectrin molecules with actin to form a two-dimensional meshwork. Principal that can be derived, from the erythrocyte membrane, is that spectrin alone does not polymerize or assemble into higher order structures without the aid of accessory proteins. This chapter discusses ankyrins that comprise an important class of spectrin-organizing proteins that are candidates to link a number of integral membrane proteins to the spectrin skeleton in specialized plasma membrane domains. The chapter discusses ankyrin structure of ankyrins being a multigene family, functional diversity of ankyrin, because of alternative splicing of messenger RNA (mRNA) and of mapping the binding sites of ankyrin. Ankyrins are a family of structural proteins, associated with the plasma membrane, that are candidates to link integral membrane proteins to the spectrin skeleton. Ankyrin-binding proteins include three different ion channels: the anion exchanger of erythrocytes and kidney collecting ducts, the Na + /K + - adenosine triphosphate (ATP)ase of kidney distal tubules, and the voltage-dependent sodium channel of the brain.