Protection of marsupial young : immune mechanisms which protect the developing tammar wallaby (Macropus eugenii)
Creators: name: Edwards, Melanie
Publisher: name: The Australian National University
Year: 2013
Subjects: subject: Macropus eugenii Development
subject: Marsupials Reproduction.
subject: Macropus eugenii Genetics
subject: Natural immunity
subject: Gene expression

description: The newborn marsupial is born at a highly altricial stage of development when compared to eutherian newborn mammals. Interestingly, the marsupial young are born into a non-sterile environment and lack a developed immune system which prevents them from mounting an adaptive immune response. Two reviews are presented in this thesis. The first review examined the complementary mechanisms which protect the developing marsupial young. Immune protection through forms of innate immunity and maternal contributions has been examined in marsupials. However, as there are many facets to immune protection, our understanding of the protection of the developing marsupial young is far from complete and much of the developing marsupial's innate immune system remains unexplored. Importantly, the review also recognised that the availability of marsupial genomes should be exploited to help direct further research on the protection of marsupial young. The second review examined the role of the pouch in marsupial reproduction. While it is clear that the pouch provides immune protection to those species that have a pouch, the pouch cannot provide immune protection to the young of those species without a pouch. Thus, instead of using the pouch to explain immune protection of marsupial young, the review examined the role of the pouch in supporting highly altricial young and promoting reproductive success in various environments where a pouch may confer significant advantages over free hanging young. The reviews set the direction for the experimental research presented in this thesis. The model species tammar wallaby (Macropus eugenii) was used to further examine innate immune genes. First, innate immune genes, mucin and lysozyme were identified or predicted in the tammar wallaby. The mucin and lysozyme genes were then physically mapped to conserved regions of the tammar wallaby genome which facilitated the confirmation of the identification of the genes. Second, the expression of immune genes was examined in the skin and lung of developing tammar wallabies considered immune-incompetent and immune-competent using transcriptome sequencing. There were 390 and 429 immune genes expressed in developing tammar wallaby skin and lung, respectively, suggesting that both tissues play a role in immune defense. Unexpectedly, mucin and lysozyme were not expressed in the skin and lung of wallabies considered to be immune-incompetent. Further, enrichment analysis of genes identified in Gene Ontology terms showed that specific immune genes, complement component 3, complement factor B and apolipoprotein A1, have increased expression in the skin and lung of wallabies considered immune-incompetent. The increased expression of the immune genes suggests that there may be specific innate immune system processes in play to compensate for the delayed development of the adaptive immune system in marsupial. The research presented in this thesis identified gaps in the research of immune protection of marsupial young and identified, mapped and examined the expression of innate immune genes in the developing tammar wallaby. Thus, we are closer to understanding the complexity of the developing marsupial immune system. The identification of immune genes and their expression, lays the foundation for further functional research in marsupial developmental immunology.