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

Ronggai Li,Helen Dooley,Tiehui Wang,Christopher J Secombes,Steve Bird

doi:10.1016/j.dci.2011.11.010

Abstract

B-cell activating factor (BAFF), also known as tumour necrosis factor (TNF) ligand superfamily member 13B, is an important immune regulator with critical roles in B-cell survival, proliferation, differentiation and immunoglobulin secretion. A BAFF gene has been cloned from spiny dogfish (Squalus acanthias) and its expression studied. The dogfish BAFF encodes for an anchored type-II transmembrane protein of 288 aa with a putative furin protease cleavage site and TNF family signature as seen in BAFFs from other species. The identity of dogfish BAFF has also been confirmed by conserved cysteine residues, and phylogenetic tree analysis. The dogfish BAFF gene has an extra exon not seen in teleost fish, birds and mammals that encodes for 29 aa and may impact on receptor binding. The dogfish BAFF is highly expressed in immune tissues, such as spleen, and is up-regulated by PWM in peripheral blood leucocytes, suggesting a potentially important role in the immune system.

Highlights

Cellular precursors of lymphocyte-like cells have recently been identified in jawless fish, the appearance of an adaptive immune system containing immunoglobulins (Igs), T-cell receptors (TCRs) and major histocompatibility complex (MHC) molecules is confined to jawed vertebrates (Flajnik and Kasahara, 2010; Haire et al, 2000)
Two rapid amplification of cDNA ends (RACE)-PCR products overlapping with the partial BAFF cDNA were obtained, and when cloned and sequenced were found to contain the full-length spiny dogfish BAFF cDNA
The full-length spiny dogfish BAFF cDNA consists of 1333 bp, with an open reading frame (ORF) of 867 bp, coding for a predicted protein of 288 aa (Fig. 1)

Summary

Introduction

Cellular precursors of lymphocyte-like cells have recently been identified in jawless fish, the appearance of an adaptive immune system containing immunoglobulins (Igs), T-cell receptors (TCRs) and major histocompatibility complex (MHC) molecules is confined to jawed vertebrates (Flajnik and Kasahara, 2010; Haire et al, 2000). Cartilaginous fish were one of the earliest groups of jawed vertebrates to appear and diverged from a common ancestor with other jawed vertebrates around 500 million years ago. They comprise approximately 700 extant species that include chimeras, sharks, skates and rays. The adaptive humoral immune system in this lineage was, until recently, considered to be relatively primitive and based solely upon low-affinity IgM responses (Clem et al, 1967; Makela and Litman, 1980). Shark IgM is produced in two forms, a monomeric (mIgM) and pentameric (pIgM) form (Clem et al, 1967), which do

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