Date of Degree
PhD (Doctor of Philosophy)
Anatomy and Cell Biology
John D. Colgan
B lymphopoiesis requires a network of transcription factors that orchestrate changes in gene expression amidst immunoglobulin gene rearrangement and periods of cell proliferation. Although proteins required for the function of this network have been identified, the precise mechanisms that coordinate these processes as hematopoietic progenitors differentiate into lineage-committed B cells remain unclear. Justy mice display a profound arrest of B cell development at the time of lineage commitment due to a point mutation that decreases expression of the protein Gon4-like. Previous studies suggested that Gon4-like functions to coordinate gene expression and cell division to determine cell fate, but the role of Gon4-like in B lymphopoiesis is largely unknown. Here we demonstrate that Gon4-like is required to regulate gene expression and cell cycle progression in B cell progenitors. Expression of genes required for B cell development is intact in Justy B cell progenitors, yet these cells fail to repress genes that promote the development of alternative lineages. In addition, Justy B cell progenitors are unable to upregulate genes that instruct cell cycle progression. Consistent with this, B cell progenitors from Justy mice show signs of impaired proliferation and undergo apoptosis despite containing elevated levels of activated STAT5, a transcription factor that promotes cell proliferation and survival. Genetic ablation of p53 or retroviral-mediated overexpression of pro-survival factors failed to rescue these defects. In contrast, overexpression of proteins that promote the G1/S transition of the cell cycle, including D-type cyclins, E2F2 and cyclin E, rescued pro-B cell development from Justy progenitors, an effect that was not observed upon overexpression of proteins that function during the S and G2M phases of the cell cycle. Further, overexpression of cyclin D3 led to partial restoration of gene repression in Justy pro-B cells. Notably, Gon4-like interacted with STAT5 when overexpressed in transformed cells, suggesting Gon4-like and STAT5 function together to activate expression of STAT5 target genes. Collectively, our data indicate that Gon4-like is required to coordinate gene repression and cell cycle progression during B lymphopoiesis.
Cells of the immune system provide protection against infections within the body and are essential for life. The immune system is comprised of several different cell types that all arise from the same progenitor through a process that is not completely understood. Further, disruptions in this process can lead to the development of cancer, autoimmunity, or immune deficiencies. Thus, determining the events that are required to generate distinct immune cell types is important for understanding how diseases of the immune system can arise. The development of a particular immune cell, the B cell, requires a complicated set of instructions that coordinate appropriate gene expression patterns and cell division, and must be rigidly followed in order to successfully produce mature B cells. The work presented here describes a role for the gene Gon4-like in the regulation of B cell development. Gon4-like has not been well studied in mammals and its role in B cell development is largely unknown. We demonstrate that Gon4-like is required to regulate changes in gene expression that distinguish B cells from other cells of the immune system. In addition, we show that Gon4-like is required to promote the expression of genes that instruct cell division, an essential process during development. Therefore, Gon4-like is required to coordinate gene expression changes and cell division in B cell progenitors. This work furthers our understanding of the development of B cells and may lead to new insights regarding diseases that arise due to disruptions in this process.
publicabstract, B cell development, Cell cycle, Cyclin D3, Gene expression, Gon4-like, proliferation
Copyright 2015 Jennifer Yamaoka Barr