Vertebrate species that bear live young have overcome the evolutionary challenge of maintaining both a functional adaptive immune system and viviparous life cycle. In normal pregnancy, viviparous mothers are able sustain and nourish a fetus that is genetically half non-self without mounting an immunological attack. In 1953 Sir Peter Medawar brought attention to the “enigma of the fetal graft” and immunologists have been puzzling out the intricacies of fetal tolerance ever since. Although viviparity has evolved in all jawed vertebrate lineages aside from Aves, the vast majority of reproductive immunology research has been limited to eutherian mammals. There are insights to be gained by examining the reproductive immunology of other viviparous lineages. Marsupials, which share a common viviparous ancestor with eutherians, could be key in highlighting the most ancestral of mammalian characteristics.
The gray short-tailed opossum, Monodelphis domestica, is a model marsupial species with a sequenced and well-annotated genome. Transcriptomes of pregnant and non- pregnant M. domestica uterine tissues were assessed by Next Generation RNA-Seq techniques. Global gene transcription profiles were generated for opossum uterine tissue from pregnant and control animals. Using multiple differential expression algorithms thousands of genes were determined to be differentially transcribed. Notable was the contribution of immune related genes to those most differentially abundant among the transcripts. Of particular interest were genes coding for pro-inflammatory cytokines and complement components, both known to be regulated in eutherian pregnancy. To extend the RNA-Seq results further, quantitative real-time PCR was used to assess transcript abundance of a subset of cytokines and complement components. The results revealed that the spike of increased inflammation is associated with parturition in the opossum consistent with its ancient role in birth in mammals. In addition, complement components were suppressed in the data set throughout pregnancy, consistent with regulation of this immune mechanism being critical for sustaining normal pregnancy in marsupials as it is in eutherians. Overall, the results presented support active regulation of some immune mechanisms during marsupial pregnancy and provide a basis for understanding the evolution of parturition mechanisms.
marsupial, reproductive immunology, pregnancy, evolution
Level of Degree
UNM Biology Department
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Hansen, Victoria L.. "Immunology of the gray short-tailed opossum during pregnancy and prenatal development." (2017). https://digitalrepository.unm.edu/biol_etds/203