Veterinary Immunology and Immunopathology 136 (2010) 235–247 Contents lists available at ScienceDirect Veterinary Immunology and Immunopathology journal homepage: www.elsevier.com/locate/vetimm Research paper Molecular characterisation of the CD79a and CD79b subunits of the B cell receptor complex in the gray short-tailed opossum (Monodelphis domestica) and tammar wallaby (Macropus eugenii): Delayed B cell immunocompetence in marsupial neonates Louise Duncan a,∗ , Koa Webster a , Varun Gupta a , Sham Nair a , Elizabeth Deane b a Department of Biological Sciences, Faculty of Science, Macquarie University, Eastern Road, North Ryde, NSW 2109, Australia b The Chancellery, The Australian National University, Canberra, ACT 0200, Australia article info Article history: Received 26 May 2009 Received in revised form 15 March 2010 Accepted 16 March 2010 Keywords: B cell receptor complex CD79 cDNA cloning Gene structure Marsupial Opossum Tammar abstract The B cell receptor (BCR) is a multiprotein complex that is pivotal to antigen recognition and signal transduction in B cells. It consists of an antigen binding component, membrane Ig (mIg), non-covalently associated with the signaling component, a disulphide-linked het- erodimer of CD79a and CD79b. In this study, the gene and corresponding cDNA for CD79a and CD79b in the gray short-tailed opossum, as well as the cDNA sequences for CD79a and CD79b in the tammar wallaby, are described. Many of the structural and functional features of CD79a and CD79b were conserved in both marsupials, including the ITAM regu- latory motif in the cytoplasmic tails of both subunits. The marsupial CD79 sequences shared a high degree of amino acid identities of 76% (CD79a) and 72% (CD79b) to each other, as well as 60–61% (CD79a) and 58–59% (CD79b) with their eutherian counterparts. RT-PCR analysis of CD79a and CD79b transcripts in the immune tissues of tammar pouch young revealed CD79a transcripts in the bone marrow, cervical thymus and spleen at day 10 post- partum. CD79b transcripts were detected in the bone marrow and cervical thymus at day 10 but were not detected in the spleen until day 21 postpartum. These results suggest that a functional BCR may not be assembled until day 21 postpartum and the tammar neonate may not be capable of mounting an effective adaptive immune response until this time. The molecular information presented here will allow further investigation of the role of the CD79 subunits in marsupial B cell signaling, especially during ontogeny and disease. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The mammalian CD79a (Ig-) and CD79b (Ig-) mem- brane proteins are expressed on B cells as a disulphide- linked heterodimer that associates non-covalently with membrane Ig (mIg) to form the B cell receptor (BCR) com- plex, a multiprotein structure that is pivotal to antigen recognition and signal transduction in B cells (reviewed in ∗ Corresponding author. Tel.: +61 2 9850 9259; fax: +61 2 9850 9671. E-mail address: lduncan@bio.mq.edu.au (L. Duncan). DeFranco, 1993; Reth, 1992). Whilst the mIg component is responsible for binding antigen, the cytoplasmic tail of the mIg heavy chain is very short and therefore incapable of transmitting activating signals to the inside of the cell. Thus, it is the CD79 subunits of the BCR that mediate these intracellular signaling events (Ales-Martinez et al., 1991; Reth et al., 1991). Like other signaling proteins (i.e. CD3 receptors and Fc receptors), the cytoplasmic tail of CD79a and CD79b contain an immuno-receptor tyrosine-based activation motif (ITAM) (Reth, 1989). In B cells, antigen- induced clustering of the BCR triggers the phosphorylation of the ITAM tyrosine residues on the CD79a and CD79b sub- 0165-2427/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2010.03.013