Evolution and expression of gamma-aminobutyric acid type A receptor-associated protein from the amphioxus Branchiostoma belcheri.

The cDNA encoding a gamma-aminobutyric acid type A (GABA(A)) receptor-associated protein (GABARAP) was identified from the gut cDNA library of amphioxus Branchiostoma belcheri. It consisted of 1246 bp with a 354 bp open reading frame coding for a 117 amino acids protein of 13.9 kDa. The phylogenetic tree analysis showed that amphioxus GABARAP clustered with GABARAPs, separating from GABARAP-like proteins including amphioxus GABARAPL2. Amphioxus GABARAP gene had an exon-intron organization similar to human, mouse, zebrafish and sea squirt GABARAP homologs in terms of both exon number and sequence homology of each exon, hinting at the clue that GABARAP gene transcription is regulated similarly in all the chordates. In situ hybridization histochemistry revealed a ubiquitous expression pattern of amphioxus GABARAP gene, although it was temporally expressed specifically in the primitive gut of 2- to 10-day larvae, suggesting a conserved role of GABARAP in amphioxus as well as in mammalian species.