Identification and characterization of epsilon-sarcoglycans in the central nervous system.
Alpha-, beta-, gamma-, and delta-sarcoglycans (SGs) are transmembrane glycoprotein components of the dystrophin-associated protein (DAP) complex, which is critical for the stability of the striated muscle cell membrane. Epsilon-SG was found as a homologue of alpha-SG, but unlike other SG members, it is ubiquitously expressed in various tissues as well as in striated muscle. Moreover, mutations in the epsilon-SG gene cause myoclonus-dystonia, indicating the importance of epsilon-SG for the function in the central nervous system. To gain insight into the role of epsilon-SG, its expression and subcellular distribution in mouse tissues and especially in the mouse brain were investigated. Analysis by reverse transcription-polymerase chain reaction showed four splice variants of epsilon-SG transcripts in the mouse brain, two of which are major transcript forms. One is a conventional form including exon 8 (epsilon-SG1), and the other is a novel form excluding exon 8 but including a previously unknown exon, 11b (epsilon-SG2). Immunoblot analysis using various mouse tissues indicated a broad expression pattern for epsilon-SG1, but epsilon-SG2 was expressed exclusively in the brain. Therefore, both epsilon-SG isoforms coexist in various regions of the brain. Furthermore, these isoforms were found in neuronal cells using immunohistochemical analysis. Subcellular fractionation of brain homogenates, however, indicated that epsilon-SG1 and epsilon-SG2 are relatively enriched in post- and pre-synaptic membrane fractions, respectively. These results suggest that the two epsilon-SG isoforms might play different roles in synaptic functions of the central nervous system.
Nishiyama
Akiyo
A
Department of Molecular Therapy, National Institute of Neuroscience, Ogawahigashi-cho, Kodaira, Tokyo, Japan.
Endo
Takeshi
T
Takeda
Shin'ichi
S
Imamura
Michihiro
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000166:cytology / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D002490:Central Nervous System / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D049031:Sarcoglycans; D013347:Subcellular Fractions / Q000378:metabolism; D013569:Synapses / Q000502:physiology; D014018:Tissue Distribution
D003598:Cytoskeletal Proteins; D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D049031:Sarcoglycans