Polarizing cues during mitosis can result in the process of asymmetric cell division (ACD), in which molecules differentially segregate to the two daughters. ACD has important functions in differentiation and development, with critical roles in stem cell renewal, and has been described following activation of T and B lymphocytes. In T cells, ACD can apparently result in daughters with distinct functional cell fates. We have found that in CD8+ T cells, ACD is associated with asymmetric segregation of c-Myc in telophase, which is then maintained in first division daughter cells. Further, we have found that the distribution of amino acid transporters, amino acid levels, TORC1 activity, and c-Myc correlate as activated T cells undergo the first round of division, and the maintenance of the differential c-Myc levels depends on amino acid availability, glutaminolysis, and TORC1 activity. This application is based on our central hypothesis that asymmetry, established via the coordinate polarization of surface molecules, including amino acid transporters, to the site of T cell receptor (TCR) activation, creates a metabolic, feed-forward process that sustains TORC1, c-Myc, epigenetics, and cell fate. To explore this hypothesis in detail, we will ask: 1. How is asymmetric division in CD8+ T lymphocytes established? Here we will examine the initial events that lead to asymmetric assortment of amino acid transporters, TORC1, and c-Myc upon the first division in CD8+ T lymphocytes, testing the idea that it is the polarization of the microtubule organizing center, transporters, and TORC1 activity that drives ACD. We will explore roles for the interactions of TCR signaling components, cytoskeleton, and the translation machinery in the asymmetrical distribution of these critical determinants of T lymphocyte fate, and examine how they influence the function and expression of TORC1, c-Myc, and other asymmetrically-distributed functional molecules. 2. How is asymmetry, once established, maintained in the daughter cells and their progeny? Based on our data, we hypothesize that metabolic differences in the daughters arising from ACD, established by asymmetric assortment of amino acid transporters, maintains and consolidates asymmetry via feed-forward mechanisms. We will perturb the elements of this positive feed-back pathway to alter the phenotypes and functions of either daughter, and examine roles for translation, transcription, and epigenetic changes in maintaining asymmetry. 3. What are the roles of asymmetry in the first division of CD8+ T cells in vivo? The daughters of asymmetric division of T cells appear to be endowed with distinct fates, characterized by effector-like and memory-like properties, however the contribution of ACD to immune responses remains controversial. We will employ approaches to barcoding, single cell mRNA expression, and lineage tracing to examine how cells that are apparently committed to a cell fate may be re-directed to a different fate via subsequent asymmetric division or alterations in asymmetry, and how these contribute to immune responses in vivo. These studies will provide fundamental new insights into the process of ACD and its consequences in CD8+ T cells.
Asymmetric cell division (ACD) is a process whereby a dividing cell produces two distinct daughter cells. T lymphocytes undergo ACD following initial recognition of antigen, and the daughters display different cell behaviors. We propose a model for the metabolic control of ACD in T cells and explore its applications.
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