Biological role of the lineage-determining transcription factor Spi-C in B cells

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B lymphocytes are white blood cells in our bodies that make antibodies necessary to fight infection by bacteria and viruses. B lymphocytes develop in the bone marrow through a series of stages that alternate between dividing (proliferating) or resting (quiescent). To make antibodies, B lymphocytes must recombine their immunoglobulin genes using a dangerous enzyme called the recombinase-activating gene (RAG). If recombination occurs during cell division, off-target effects could lead to DNA damage and cell death. Spi-C is a transcription factor, a protein located in the nucleus of cells, that turns other genes on or off. Spi-C is a lineage-determining transcription factor: it can tell cells how to develop by activating or repressing programs of gene expression. Spi-C is known to be expressed in response to RAG-induced DNA damage during B cell development. In preliminary data, we show that Spic is upregulated in response to heme or culture conditions that induce quiescence; whereas Spic is downregulated in response to cytokines that induce cell division. The long-term goal of this research program is to identify the factors that govern cell cycle arrest and cell cycle entry in developing B cells. The short-term goals of our research program are to determine what factors outside the cell activate Spi-C expression, to determine what gene expression programs are regulated by Spi-C, and to determine how Spi-C regulation impacts antibody production. Based on our preliminary data, we hypothesize that Spic is upregulated in response to NF-kappaB-dependent or heme-induced signaling; and downregulated in response to cell cycle progression. To test this hypothesis, we will investigate what regulates Spi-C expression (upstream) and what genes are regulated by Spi-C (downstream). Upstream, we will determine the detailed mechanism by which Spi-C is upregulated in response to heme or NF-kappaB signaling; and the mechanism by which Spi-C is downregulated in response to cell cycle progression. Downstream of Spi-C, we will determine the direct target genes in B cells using a doxycycline-inducible system. Finally, we will determine the in vivo role of Spi-C in the B cell lineage in response to intracellular heme and extracellular heme generated by hemolysis. This work is important because it will provide important insight into the mechanisms underlying B cell differentiation in response to environmental signals. This knowledge can be used to improve antibody responses to bacterial or viral infections. This work will be carried out by HQP primarily at the Masters and undergraduate levels, providing training in research, oral presentation, and writing skills that can be leveraged for future employment and further professional training.