Characterisation and expression analysis of B-cell activating factor (BAFF) in spiny dogfish (Squalus acanthias): Cartilaginous fish BAFF has a unique extra exon that may impact receptor binding

► We cloned BAFF from a cartilaginous fish, the spiny dogfish (Squalus acanthias). ► It is expressed as a type II transmembrane protein with a furin cleavage site. ► Cartilaginous fish BAFF has an additional exon compared to that of other species. ► The exon encodes a 29 aa extension in the a-a′ loop, near the receptor binding site. ► It is highly expressed in immune tissues in vivo and up-regulated by PWM in vitro.