α-, β-, γ-, and δ-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. ϵ-SG was found as a homologue of α-SG, but unlike other SG members, it is ubiquitously expressed in various tissues as well as in striated muscle. Moreover, mutations in the ϵ-SG gene cause myoclonus-dystonia, indicating the importance of ϵ-SG for the function in the central nervous system. To gain insight into the role of ϵ-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 ϵ-SG transcripts in the mouse brain, two of which are major transcript forms. One is a conventional form including exon 8 (ϵ-SG1), and the other is a novel form excluding exon 8 but including a previously unknown exon, 11b (ϵ-SG2). Immunoblot analysis using various mouse tissues indicated a broad expression pattern for ϵ-SG1, but ϵ-SG2 was expressed exclusively in the brain. Therefore, both ϵ-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 ϵ-SG1 and ϵ-SG2 are relatively enriched in post- and pre-synaptic membrane fractions, respectively. These results suggest that the two ϵ-SG isoforms might play different roles in synaptic functions of the central nervous system.

DOI: 10.1016/j.molbrainres.2004.01.012
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