A new variant of proline-rich membrane anchor (PRiMA) of acetylcholinesterase in chicken: Expression in different muscle fiber types

Proline-rich membrane anchor (PRiMA) is a molecule to organize acetylcholinesterase (AChE) into tetrameric globular form (G4) that anchors onto the plasma membrane in brain and muscle. In mammal, PRiMA is encoded by a single gene with two splicing variants, PRiMA I and PRiMA II: PRiMA II is different to PRiMA I by its absence of a C-terminal cytoplasmic domain. The existence of these isoforms has not been revealed in avian specie. By using RT-PCR and bioinformatic analyses, two splicing variants of PRiMA were identified in chicken cerebrum. One variant contains very similar domains as compared to mammalian PRiMA I. The other variant, named as PRiMA II, has a very distinct cytoplasmic C-terminus of having 26 amino acids. Both forms of chicken PRiMA were able to organize the formation of G4 AChE when that was over expressed together with AChET subunit in cultured cells. The level of PRiMA mRNA, mainly PRiMA I, was higher in slow-twitch muscle than that of in fast-twitch muscle of chicken. This finding suggests that the muscle fiber type-specific expression of G4 AChE in chicken could be a result of the different expression pattern of PRiMA in fast- and slow-twitch muscles.