Molecular cloning, characterization and tissue distribution of six splice variants of activin type IIA receptor (ActRIIA) from grass carp (Ctenopharyngodon idellus)

Abstract

Activin type II receptor (ActRII) is crucial for the assembly of the ligand/receptor complex and the activation of downstream cascades in activin signaling pathway. In this study, we identified six variants of grass carp ActRIIA which can be generated through three alternative splicing events (defined as AS1, AS2 and AS3). AS1 induces a spliced segment encoding 14 amino acids located in the external juxtamembrane region of the receptor. However, both AS2 and AS3 occur at the same cleavage site of kinase domain and induce a premature termination codon. Indeed, AS2 inserts a fragment of 79 bp while AS3 generates a new 3′ terminal of cDNA with poly(A) signals. The full length cDNA of the shortest variant was shown to be 2001 bp encoding 514 amino acids with sequence identity of 79-95% to counterparts in other species. Homology modeling studies showed grass carp ActRIIA exhibits a characteristic three-finger toxin fold in the extracellular domain and a conserved bilobal architecture in the intracellular kinase domain. Semi-quantitative RT-PCR analysis revealed that six variants showed different expression patterns in selected tissues of grass carp. This study will be helpful for a better understanding of the physiological role of activin signaling in lower vertebrates.