The thymus is a primary lymphoid organ responsible for the development of T-cells and the establishment of central tolerance. Its major structural and functional component, the thymic epithelium, can be subdivided into cortical and medullary thymic epithelial cells (TECs). These two lineages are believed to arise from a common progenitor/stem cell early in embryonic development and go through distinct maturation stages before turning into short-lived terminally differentiated cells (Tykocinski et al., 2008).

The establishment of central tolerance relies on the capacity of medullary thymic epithelial cells (mTECs) to express self-antigens, present them to developing thymocytes and mediate negative selection of potentially self-reactive T-cells. One of the most puzzling features of these mTECs is their ability to express a plethora of tissue-restricted self-antigens, a phenomenon called promiscuous gene expression (pGE). The molecular control of pGE is only poorly understood. Our recent studies indicate that pGE is regulated at the epigenetic level (Tykocinski et al., 2010) and by posttranscriptional mRNA modifications (unpublished), however the exact mechanisms remain to be elucidated.

miRNAs are 22-23 nucleotide long RNA molecules that mediate gene expression control by repressing translation of their target mRNAs. The absence of Dicer, the key enzyme in miRNA biogenesis, results in premature thymic involution and progressive disorganization of thymic epithelium (Papadopoulou et al., 2012). Our unpublished data suggest that a total lack of miRNAs in TECs also causes defects in TEC maturation and a gradual loss of pGE. The goal of this PhD project is to analyse the role of particular miRNAs and their targets in mTEC progenitor maintenance and development and in the molecular control of pGE.

Candidates are expected to have a M.Sc. degree in biology/biomedicine and experience in basic molecular biology techniques and a strong interest in immunology, developmental biology and RNA biology is an advantage.

The methods to be used will include primary cell isolation and culture, flow cytometry, histology, organotypic culture, stem cell culture, miRNA and mRNA expression analysis.

Olga Ucar
o.ucar@dkfz.de
German Cancer Research Center
Heidelberg

Ansprechpartner: Olga Ucar, o.ucar@dkfz.de