Year: 2007
Type: dissertation
Abstract: Thymocyte development is a complex process that requires precise regulation of\ndifferentiation and proliferation. Basic helix-loop-helix (bHLH) transcription factors\nhave been shown to be crucial for proper T cell development. HEB and E2A are\nstructurally and functionally related E proteins of the bHLH family. These proteins\ndirectly regulate the expression of a number of genes essential for lymphocyte\ndevelopment in a lineage- and stage-specific manner. Abrogation or compromise of their\nfunction results in the manifestation of B and T cell developmental defects.\nGenetic and biochemical studies have provided evidence of a significant degree of\nfunctional redundancy among E proteins. The existence of compensational abilities\namong different E proteins has hampered the investigation and elucidation of E protein\nfunction. As such, single gene knockouts demonstrate only limited defects in lymphocyte\ndevelopment. Double E2A-HEB knockouts that could eliminate E protein redundancy\nare embryonic lethal. In addition, conventional gene knockouts are not well-suited for\ndiscerning between intrinsic and extrinsic defects caused by E protein disruption.\nTo eliminate functional compensation and to test the T cell intrinsic roles of E\nproteins during thymocyte development, we developed a conditional HEB-E2A double\nknockout. Specifically, we employed a loxP/Lck-Cre recombinase system to drive E\nprotein deletion during early thymocyte development. Using this approach, we were able\nto reveal overlapping roles for HEB and E2A in thymocyte development that had been\nobscured in previous single gene knockout studies.\nWe find that simultaneous deletion of HEB and E2A results in a severe block in\nthymocyte development at the DN to DP stage transition. This developmental block is\naccompanied by a dramatic decrease in total thymic cellularity, an increase in apoptosis,\nand a reduction of pTα expression. These developmentally arrested thymocytes exhibit\nincreased proliferation in vivo and dramatic expansion ex vivo in response to IL-7\nsignaling. Our findings suggest that E2A and HEB are not only critical for the regulation\nof T cell differentiation but are also necessary to retain developing thymocytes in cell\ncycle arrest prior to pre-TCR expression. Together, these results imply that E proteins\nare required to coordinate thymocyte differentiation and proliferation.
Source: DukeSpace (Duke University)
Author: Jason Wojciechowski
Language: English
Topic: T-cell and B-cell Immunology
Subfield: Immunology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W60865655