Abstract
CD79α (also known as Igα) is a component of the B cell antigen receptor complex and plays an important role in B cell signalling. The CD79α 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) CD79α (SaCD79α) is described and its expression studied under constitutive and stimulated conditions. The spiny dogfish CD79α cDNA contains an open reading frame of 618 bp, encoding a protein of 205 amino acids. Comparison of the SaCD79α 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 SaCD79α 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 CD79α 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, CD79α 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 CD79α 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.
Highlights
Cartilaginous fish were one of the earliest groups of jawed vertebrates to emerge, diverging from a common ancestor with other jawed vertebrates around 500 million years ago
Whilst CD79a has been studied in mammals [26e28] and, more recently, in some bony fish [29,30], nothing is known about CD79a or B cell receptor (BCR) signalling in cartilaginous fish
The molecular information gained will allow us to begin to investigate BCR signalling in cartilaginous fish
Summary
Cartilaginous fish (chimeras, sharks, rays and skates) were one of the earliest groups of jawed vertebrates to emerge, diverging from a common ancestor with other jawed vertebrates around 500 million years ago They are the most ancient vertebrate group to possess an immune system based upon immunoglobulin (Ig), T cell receptor (TCR) and major histocompatibility complex (MHC) molecules [1] and so are pivotal in understanding the evolution of adaptive immunity. Cartilaginous fish Ig genes are organised in clusters, rather than the Abbreviations: Ig, immunoglobulin; BCR, B cell receptor; TM, transmembrane; CYT, cytoplasmic tail; TCR, T cell receptor; ITAM, immune-receptor tyrosine-based activation motif Cartilaginous fish lack both bone marrow and a lymphatic system but, in addition to a thymus, spleen and gut associated lymphoid tissue (GALT), they have an epigonal organ (associated with the gonads) and a Leydig organ (associated with the oesophagus) [9]. IgM and IgNAR are expressed at high levels in the spleen, liver, gill, kidney and epigonal organ, whereas IgW is predominantly expressed in the spleen, epigonal and pancreas [13]
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