TCRμ recombination and transcription relative to the conventional TCR during postnatal development in opossums.
Parra, Z.E., Baker, M. L., Lopez, A. M., Trujillo, J., Volpe, J. M and Miller, R.D.
Abstract:
Marsupials are a distinct lineage of mammals notable for giving birth to highly altricial (relatively less developed) young. The recent discovery of a unique TCR chain in marsupials, TCRμ, raises questions about its possible role in early development. Here we compare the timing of V(D)J recombination and appearance of TCRμ transcripts relative to the conventional TCRα, β, γ and δ mRNA during postnatal development in the opossum. There are two TCRμ transcript isoforms, TCRμ1.0 and TCRμ2.0. TCRμ1.0, which uses pre-joined V(D)J segments, is detectable as early as day 1, when the thymus is primarily undifferentiated epithelium. The other isoform, TCRμ2.0, which requires V(D)J recombination and contains an unusual double V configuration, is not detectable until day 13 when the thymus is histologically mature. Surprisingly we were able to detect TCRα, β and δ mRNA transcribed from loci that had completed V(D)J recombination as early as day 1 as well. At this early age there is apparent evidence for preference in the V segments used in the TCRα and β genes. In the case of Vα this preference appears to be associated with position in the TCRα/δ locus. In Vβ however preference may be due to the use of microhomology in the V, D, and J segments. Mature TCRγ transcripts were not detected until day 8 suggesting that, in contrast to eutherian mammals, in the opossum αβT cell development precedes γδT cell development. The results support that there may be differences in T cell subset development between marsupials and placental mammals.