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Subunit Isoforms (subunit + isoform)

Distribution by Scientific Domains

Life Sciences	66%
Medical Sciences	33%

Selected Abstracts

Distribution and functional characterization of human Nav1.3 splice variants

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005
R. Thimmapaya
Abstract The focus of the present study is the molecular and functional characterization of four splice variants of the human Nav1.3 , subunit. These subtypes arise due to the use of alternative splice donor sites of exon 12, which encodes a region of the , subunit that resides in the intracellular loop between domains I and II. This region contains several important phosphorylation sites that modulate Na+ channel kinetics in related sodium channels, i.e. Nav1.2. While three of the four Nav1.3 isoforms, 12v1, 12v3 and 12v4 have been previously identified in human, 12v2 has only been reported in rat. Herein, we evaluate the distribution of these splice variants in human tissues and the functional characterization of each of these subtypes. We demonstrate by reverse transcriptase-polymerase chain reaction (RT-PCR) that each subtype is expressed in the spinal cord, thalamus, amygdala, cerebellum, adult and fetal whole brain and heart. To investigate the functional properties of these different splice variants, each , subunit isoform was cloned by RT-PCR from human fetal brain and expressed in Xenopus oocytes. Each isoform exhibited functional voltage-dependent Na+ channels with similar sensitivities to tetrodotoxin (TTX) and comparable current amplitudes. Subtle shifts in the V1/2 of activation and inactivation (2,3 mV) were observed among the four isoforms, although the functional significance of these differences remains unclear. This study has demonstrated that all four human splice variants of the Nav1.3 channel , subunit are widely expressed and generate functional TTX-sensitive Na+ channels that likely modulate cellular excitability. [source]

Two Na,K-ATPase ,2 subunit isoforms are differentially expressed within the central nervous system and sensory organs during zebrafish embryogenesis

DEVELOPMENTAL DYNAMICS, Issue 2 2002
Johannes R. Rajarao
Abstract We have identified cDNAs encoding a second zebrafish ortholog of the human Na,K-ATPase ,2 subunit. The ,2b cDNA encodes a 292 amino acid-long polypeptide with 74% identity to the previously characterized zebrafish ,2a subunit. By using a zebrafish meiotic mapping panel, we determined that the ,2b gene (atp1b2b) was tightly linked to markers on linkage group 5, whereas the ,2a gene was located on linkage group 23. In situ hybridization analysis shows that in developing zebrafish embryos, atp1b2a and atp1b2b are predominantly expressed in the nervous system. ,2a transcripts were abundantly expressed throughout brain as well as spinal cord neurons and lateral line ganglia. In contrast, ,2b mRNA expression was primarily detected in sensory organs, including retina, otic vesicles, and lateral line neuromast cells. These results suggest that the ,2a and ,2b genes play distinct roles in developing brain and sensory organs, and raise the possibility that the functions encoded by the single mammalian ,2 gene may be partitioned between the two zebrafish ,2 orthologs. © 2002 Wiley-Liss, Inc. [source]

Rescue of ,2 subunit-deficient mice by transgenic overexpression of the GABAA receptor ,2S or ,2L subunit isoforms

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2000
Kristin Baer
Abstract The ,2 subunit is an important functional determinant of GABAA receptors and is essential for formation of high-affinity benzodiazepine binding sites and for synaptic clustering of major GABAA receptor subtypes along with gephyrin. There are two splice variants of the ,2 subunit, ,2 short (,2S) and ,2 long (,2L), the latter carrying in the cytoplasmic domain an additional eight amino acids with a putative phosphorylation site. Here, we show that transgenic mice expressing either the ,2S or ,2L subunit on a ,2 subunit-deficient background are phenotypically indistinguishable from wild-type. They express nearly normal levels of ,2 subunit protein and [3H]flumazenil binding sites. Likewise, the distribution, number and size of GABAA receptor clusters colocalized with gephyrin are similar to wild-type in both juvenile and adult mice. Our results indicate that the two ,2 subunit splice variants can substitute for each other and fulfil the basic functions of GABAA receptors, allowing in vivo studies that address isoform-specific roles in phosphorylation-dependent regulatory mechanisms. [source]

Expression of proteasome subunit isoforms during spermatogenesis in Drosophila melanogaster

INSECT MOLECULAR BIOLOGY, Issue 6 2002
J. Ma
Abstract In this study, we sought to identify and characterize all the proteasome genes of Drosophila melanogaster. Earlier work led to the identification of two genes encoding ,4-type 20S proteasome subunit isoforms that are expressed exclusively in the male germline. Here we extend these results and show that six of the 20S proteasome subunits, and four of the 19S regulatory cap subunits, have gene duplications encoding male-specific isoforms. More detailed analyses of two of these male-specific subunits (Pros,3T and Pros,6T), using GFP-tagged reporter transgenes, revealed that they are predominantly localized to the nucleus at later stages of spermatogenesis and are present there in mature, motile sperm. These results suggest a possible role of a ,spermatogenesis-specific' proteasome in sperm differentiation and/or function. [source]

Hydrogen peroxide induces expression and activation of AMP-activated protein kinase in a dental pulp cell line

INTERNATIONAL ENDODONTIC JOURNAL, Issue 3 2008
Y. Fukuyama
Abstract Aim, To investigate the effects of hydrogen peroxide on cell viability and expression and activation of AMP-activated protein kinase (AMPK) in rat dental pulp cell line RPC-C2A. Methodology, RPC-C2A cells derived from rat dental pulp were maintained in MEM supplemented with 10% FBS at 37 °C, in a humidified atmosphere at 5% CO2. Cells were cultured in the presence or absence of H2O2 for up to 60 min at concentrations of from 0.1 to 3.0 mmol L,1. Cell viability was analysed by WST-1 reduction assay. Expression of AMPK subunit isoforms was analysed by Western blotting using antibodies to the catalytic ,1 and regulatory ,1 and ,1 subunit isoforms. The effect of silencing AMPK,1 on cell viability was determined using siRNA. Results, Exposure to H2O2 decreased cell viability in a time- and dose-dependent manner. The catalytic AMPK,1 subunit and its activated form, phospho-AMPK,, increased with exposure to H2O2 in a time- and dose-dependent manner, whereas the regulatory ,1 and ,1 subunits showed no change. Downregulation of AMPK,1 resulted in a reduction in cell viability in H2O2 -treated cells at a concentration of 0.1 mmol L,1 for 30 min incubation, indicating an increased sensitivity to H2O2. Conclusions, Reactive oxygen induced energy fuel gauge enzyme AMPK, expression and its activation by phosphorylation in RPC-C2A cells, suggesting that AMPK is essential for protection against H2O2 -induced nonapoptotic cell death. Therefore, AMPK may be a therapeutic modulation target for treatment of the dentine,pulp complex injured by reactive oxygen. [source]

Consequence of the presence of two different , subunit isoforms in a GABAA receptor

JOURNAL OF NEUROCHEMISTRY, Issue 6 2005
Nathalie Boulineau
Abstract The major isoforms of GABAA receptors are thought to be composed of two ,, two , and one , subunit(s). GABAA receptors containing two ,1 subunits respond differently to the anticonvulsive compound loreclezole and the general anaesthetic etomidate than receptors containing two ,2 subunits. Receptors containing ,2 subunits show a much larger allosteric stimulation by these agents than those containing ,1 subunits. We were interested to know how receptors containing both ,1 and ,2 subunits, in different positions respond to loreclezole and etomidate. To answer this question, subunits were fused at the DNA level to form dimeric and trimeric subunits. Concatenated receptors (,1 -,1 -,1/,2 -,1, ,1 -,2 -,1/,2 -,1, ,1 -,1 -,1/,2 -,2 and ,1 -,2 -,1/,2 -,2) were expressed in Xenopus ooctyes and functionally compared in their response to the agonist GABA and to the positive allosteric modulators, loreclezole and etomidate. We have shown that (I) in the presence of both ,1 and ,2 subunits in the same pentamer (mixed receptors) direct gating by etomidate is similar to exclusively ,1 containing receptors; (II) In mixed receptors, stimulation by etomidate assumed characteristics intermediate to exclusively ,1 or ,2 containing receptors, but the values for the concentrations < 10 µm were always much closer to those observed in ,1 -,1 -,1/,2 -,1 receptors; and (III) mixed receptors show no positional effects. [source]

Molecular Diversity Of Vascular Potassium Channel Isoforms

CLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2002
Victoria P Korovkina
SUMMARY 1. One essential role for potassium channels in vascular smooth muscle is to buffer cell excitation and counteract vasoconstrictive influences. Several molecular mechanisms regulate potassium channel function. The interaction of these mechanisms may be one method for fine-tuning potassium channel activity in response to various physiological and pathological challenges. 2. The most prevalent K+ channels in vascular smooth muscle are large-conductance calcium- and voltage-sensitive channels (maxi-K channels) and voltage-gated channels (Kv channels). Both channel types are complex molecular structures consisting of a pore-forming , -subunit and an ancillary , -subunit. The maxi-K and Kv channel , -subunits assemble as tetramers and have S4 transmembrane domains that represent the putative voltage sensor. While most vascular smooth muscle cells identified to date contain both maxi-K and Kv channels, the expression of individual , -subunit isoforms and , -subunit association occurs in a tissue-specific manner, thereby providing functional specificity. 3. The maxi-K channel , -subunit derives its molecular diversity by alternative splicing of a single-gene transcript to yield multiple isoforms that differ in their sensitivity to intracellular Ca2+ and voltage, cell surface expression and post- translational modification. The ability of this channel to assemble as a homo- or heterotetramer allows for fine-tuning control to intracellular regulators. Another level of diversity for this channel is in its association with accessory , -subunits. Multiple , -subunits have been identified that can arise either from separate genes or alternative splicing of a , -subunit gene. The maxi-K channel , -subunits modulate the channel's Ca2+ and voltage sensitivity and kinetic and pharmacological properties. 4. The Kv channel , -subunit derives its diverse nature by the expression of several genes. Similar to the maxi-K channel, this channel has been shown to assemble as a homo- and heterotetramer, which can significantly change the Kv current phenotype in a given cell type. Association with a number of the ancillary , -subunits affects Kv channel function in several ways. Beta-subunits can induce inactivating properties and act as chaperones, thereby regulating channel cell-surface expression and current kinetics. [source]