Molecular characterisation of the tammar wallaby (Macropus eugenii) CD3 epsilon chain cDNA

Red-tailed phascogales: A review of their biology and importance as model marsupial species

There are many limitations when using traditional laboratory species. Limits on variation, may result in limited outcomes, at both the species and individual level, due to different individuals/species having diverse physiological processes, or differing molecular and genetic mechanisms. By using a variety of model species, we will be able to develop creative solutions to biological problems and identify differences of which we were not previously aware. The laboratory mouse has been a suitable model species for various mammalian studies, however most are bred specifically for laboratory research with limited variability due to selective breeding. Marsupial models offer unique research opportunities compared to eutherian models. We believe that there should be an expansion in marsupial model species, and the introduction of the red-tailed phascogale (Phascogale calura), a dasyurid marsupial, should be one of them. Phascogales are easily managed in captivity, and there are now multiple studies involving their development, reproduction, nutrition, behavior and immune system, which can serve as a baseline for future studies. The addition of the phascogale as a model species will improve future mammalian studies by introducing variability and offer alternate solutions to biological problems, particularly in the areas of genetics, nutrition, immunology, the neuro-endocrine system, and ageing, due to their semelparous reproductive strategy and hence, subsequent predictive physiology. In this review, we provide information based on existing research on red-tailed phascogales to support their inclusion as a model species.

Marsupial immunology bounding ahead

Marsupial immune responses were previously touted as ‘primitive’ but we now know that the marsupial immune system is complex and on par with that of eutherian mammals. In this manuscript we review the field of marsupial immunology, focusing on basic anatomy, developmental immunology, immunogenetics and evolution. We concentrate on advances to our understanding of marsupial immune gene architecture, made possible by the recent sequencing of the opossum, tammar wallaby and Tasmanian devil genomes. Characterisation of immune gene sequences now paves the way for the development of immunological assays that will allow us to more accurately study health and disease in marsupials.

Immunome database for marsupials and monotremes

BACKGROUND

To understand the evolutionary origins of our own immune system, we need to characterise the immune system of our distant relatives, the marsupials and monotremes. The recent sequencing of the genomes of two marsupials (opossum and tammar wallaby) and a monotreme (platypus) provides an opportunity to characterise the immune gene repertoires of these model organisms. This was required as many genes involved in immunity evolve rapidly and fail to be detected by automated gene annotation pipelines.

DESCRIPTION

We have developed a database of immune genes from the tammar wallaby, red-necked wallaby, northern brown bandicoot, brush-tail possum, opossum, echidna and platypus. The resource contains 2,235 newly identified sequences and 3,197 sequences which had been described previously. This comprehensive dataset was built from a variety of sources, including EST projects and expert-curated gene predictions generated through a variety of methods including chained-BLAST and sensitive HMMER searches. To facilitate systems-based research we have grouped sequences based on broad Gene Ontology categories as well as by specific functional immune groups. Sequences can be extracted by keyword, gene name, protein domain and organism name. Users can also search the database using BLAST.

CONCLUSION

The Immunome Database for Marsupials and Monotremes (IDMM) is a comprehensive database of all known marsupial and monotreme immune genes. It provides a single point of reference for genomic and transcriptomic datasets. Data from other marsupial and monotreme species will be added to the database as it become available. This resource will be utilized by marsupial and monotreme immunologists as well as researchers interested in the evolution of mammalian immunity.

N-terminal negatively charged residues in CD3varepsilon chains as a phylogenetically conserved trait potentially yielding isoforms with different isoelectric points: analysis of human CD3varepsilon chains

CD3varepsilon chains are essential to the structure, expression and signaling of T cell receptors. Here, we extend to human CD3varepsilon our previous data in mouse CD3varepsilon showing that, in T cells, proteolytic processing of the acidic N-terminal sequence of CD3varepsilon chains generate distinct polypeptide species that can be identified by two-dimension (IEF-SDS PAGE) electrophoresis and immunoblot. This was shown first by showing the processing of a fusion protein of GFP and the extracellular domain of mouse CD3varepsilon (mCD3GFP) expressed in Jurkat cells. Secondly, pI heterogeneity was also found in human CD3varepsilon chains immunoprecipitated from the surface of Jurkat cells or PHA blasts of human blood T lymphocytes. Comparison of CD3varepsilon chains from 27 different species shows that their N-terminal sequences share a strong acidic nature, despite the large differences in terms of length and composition, even among closely related species. Our results suggest that generation of CD3varepsilon chain isoforms with different N-terminal sequence and pI is a general phenomenon. Thus, as previously observed in the mouse, the relative abundance of CD3varepsilon chain species might regulate TCR/CD3 structure and function, including the strength of the interactions between CD3 dimers and the TCR clonotypic receptors, as well as TCR/CD3 activation thresholds. Interestingly, CD3varepsilon chains from 7 out of 27 species studied have putative N-glycosylation (NxS or NxT) motifs in their Ig extracellular domain. Their location, plus the conservation of residues involved in domain organization, the interactions with other CD3 chains, or the TCR, and signal triggering add new data useful to establish a permissive topology for the interaction between CD3 dimers and the TCR chains.

Primary structure and variation of the T-cell receptor delta-chain from a marsupial, Macropus eugenii

Although gammadelta T-cells form only a small portion of circulating T-cells in mice and humans, they are more frequent in many other types of mammals and this has lead to speculation regarding their roles and the evolutionary significance of their relative abundance. Moreover, whilst clear homologues of four types of T-cell receptor (TCR) chains (alpha, beta, delta and gamma) have been identified in vertebrates as distantly related as eutherian mammals and cartilaginous fish, there are still many gaps in our knowledge of these TCR components from various taxa. Such knowledge would further illuminate the evolution and function of these receptors and of gammadelta T-cells. Here, we report the molecular cloning of a TCR-delta chain cDNA from the tammar wallaby (Macropus eugenii) which represents the first component of the gammadelta TCR to be characterised from a marsupial. A PCR-based survey of variable (V) segment usage in tammar wallaby mammary-associated lymph node indicated that, although gammadelta T-cells may be sparse in this type of tissue, this species has at least three subfamilies of V genes that have been broadly conserved across vertebrate evolution. Two V subfamilies found in the tammar wallaby were relatively similar and may have diverged more recently, an event that probably occurred at some point in the marsupial lineage.