B cell receptor accessory molecule CD79α: characterisation and expression analysis in a cartilaginous fish, the spiny dogfish (Squalus acanthias)

CD79a (also known as Iga) is a component of the B cell antigen receptor complex and plays an important role in B cell signalling. The CD79a protein is present on the surface of B cells throughout their life cycle, and is absent on all other healthy cells, making it a highly reliable marker for B-cells in mammals. In this study the spiny dogfish (Squalus acanthias) CD79a (SaCD79a) is described and its expression studied under constitutive and stimulated conditions. The spiny dogfish CD79a cDNA contains an open reading frame of 618 bp, encoding a protein of 205 amino acids. Comparison of the SaCD79a gene with that of other species shows that the gross structure (number of exons, exon/intron boundaries, etc) is highly conserved across phylogeny. Additionally, analysis of the 5' flanking region shows SaCD79a lacks a TATA box and possesses binding sites for multiple transcription factors implicated in its B cell-specific gene transcription in other species. Spiny dogfish CD79a is most highly expressed in immune tissues, such as spleen, epigonal and Leydig organ, and its transcript level significantly correlates with those of spiny dogfish immunoglobulin heavy-chains. Additionally, CD79a transcription is up-regulated, to a small but significant degree, in peripheral blood cells following stimulation with pokeweed mitogen. These results strongly indicate that, as in mammals, spiny dogfish CD79a is expressed by shark B cells where it associates with surface-bound immunoglobulin to form a fully functional BCR, and thus may serve as a pan B cell marker in future shark immunological studies.