Coordinating Central Tolerance: Defining Distinct Roles for Nr4a1 and Nr4a3 in Thymocyte Selection
openNIAID - National Institute of Allergy and Infectious Diseases
PROJECT SUMMARY/ABSTRACT
Dr. Nielsen’s long-term goal is to understand molecular mechanisms that drive autoimmune diseases to
improve their diagnosis and treatment. This five-year research and training plan will launch her independent
career studying thymic T cell tolerance. To select a functional, self-tolerant T cell repertoire, developing
thymocytes test their vast, random array of T cell receptors (TCRs) at key checkpoints to 1) ensure MHC
restriction, 2) “tune” their capacity to distinguish self from foreign stimuli, and 3) “prune” self-reactive TCRs via
clonal deletion or diversion to a regulatory T cell (Treg) fate. Nr4a transcription factors – whose expression
scales with self-reactivity – collectively translate the TCR signals that enforce clonal deletion, Treg diversion,
and aspects of TCR “tuning.” However, distinct protein expression dynamics for family members NR4A1 and
NR4A3 suggest a “division of labor” in thymic selection which has yet to be unmasked.
This proposal’s central hypotheses are: 1) NR4A1’s low threshold for induction and rapid decay allow it
sense and tune TCR signaling during positive selection, 2) collective NR4A “dosage” determines deletion and
Treg diversion, and NR4A3’s high threshold for induction and sustained expression enforce death and
diversion of select self-reactive clonotypes in the medulla. Using biochemical assays of TCR signaling, Aim 1
characterizes how TCR tuning and NR4As operate in human thymocytes and – using genetic mouse models –
determines the roles of NR4A1 and NR4A3 in TCR tuning. Aim 2 leverages high-resolution TCR sequencing
and unbiased auto-antibody profiling (PhIP-seq) in to identify how the NR4As uniquely and cooperatively
shape the thymic TCR repertoire. Aim 3 employs single-cell transcriptomics (CITE-seq) combined with a TCR
signaling reporter to decode the transcriptional networks by which the NR4As link TCR signaling to tolerogenic
outcomes during thymic selection. Completion of this project will provide unprecedent molecular insights into
TCR signaling mechanisms and the formation of a tolerant TCR repertoire, illuminating fundamental principles
of autoimmunity and informing strategies for T cell-based immunotherapies.
Dr. Nielsen will perform this research at the University of California, San Francisco, a world-renowned
institution for immunology. She has assembled a strong mentorship and collaborative team: Dr. Julie
Zikherman (primary mentor, lymphocyte signaling), Dr. Mark Anderson (co-mentor, thymic tolerance), Dr. Ellen
Robey (T cell selection), Dr. Mike Waterfield (gene regulation), Dr. Jimmie Ye (single-cell genomic
technologies), and Dr. Wan-Lin Lo (University of Utah, TCR signaling in human cells). Through hands-on
training, formal coursework, and engagement with the global immunology community, she will develop
essential lab management skills and master advanced immunologic and genomic techniques, positioning
herself as an independent investigator driving cutting-edge research in immune tolerance.
Up to $202K
health research