Alternatively Spliced Variants of Gamma-Subunit of Muscle-Type Acetylcholine Receptor in Fetal and Adult Skeletal Muscle of Mouse

Gamma-subunit of nicotinic acetylcholine receptor is encoded by chrng gene of mouse. This gene is located on chromosome 1, spans 6.5 kb, and contains 12 exons and 11 introns. Previous studies have reported three transcript variants (C1-3) produced by alternative splicing; C1 contains all the 12 reported exons, C2 uses an in-frame alternate splice site in exon-2, and C3 produced by exon-5 skipping. These variants differ in their channel kinetics and opening times. In our study, we report the presence of two new transcript variants (T1 and T2) of chrng expressed in mouse postnatal day 3 and adult skeletal muscles. These transcripts contain novel first coding exon either N1 or N2. N1 is located in the 5′ UTR, while N2 is an extended exon-2. 5′ extension of exon-2 contains an initiation codon which produces a novel transcript variant. Either of the two exons can splice with the internal exons to produce mature transcripts making different 5′ ends of the transcripts. Consequently, the proteins encoded by these two transcripts differ at N-termini. The presence of N2 exon containing transcript was further supported by the availability of EST from the database. These new variants display heterogeneous properties. They differ in the presence of signal peptide, phosphorylation, and acetylation of their amino acid residues of the new N-termini of the gamma subunit.