The role of HEB and E2A in the regulation of T Lymphocyte development and proliferation

by Wojciechowski, Jason

Abstract (Summary)
Thymocyte development is a complex process that requires precise regulation of

differentiation and proliferation. Basic helix-loop-helix (bHLH) transcription factors

have been shown to be crucial for proper T cell development. HEB and E2A are

structurally and functionally related E proteins of the bHLH family. These proteins

directly regulate the expression of a number of genes essential for lymphocyte

development in a lineage- and stage-specific manner. Abrogation or compromise of their

function results in the manifestation of B and T cell developmental defects.

Genetic and biochemical studies have provided evidence of a significant degree of

functional redundancy among E proteins. The existence of compensational abilities

among different E proteins has hampered the investigation and elucidation of E protein

function. As such, single gene knockouts demonstrate only limited defects in lymphocyte

development. Double E2A-HEB knockouts that could eliminate E protein redundancy

are embryonic lethal. In addition, conventional gene knockouts are not well-suited for

discerning between intrinsic and extrinsic defects caused by E protein disruption.

To eliminate functional compensation and to test the T cell intrinsic roles of E

proteins during thymocyte development, we developed a conditional HEB-E2A double

knockout. Specifically, we employed a loxP/Lck-Cre recombinase system to drive E

protein deletion during early thymocyte development. Using this approach, we were able

to reveal overlapping roles for HEB and E2A in thymocyte development that had been

obscured in previous single gene knockout studies.

We find that simultaneous deletion of HEB and E2A results in a severe block in

thymocyte development at the DN to DP stage transition. This developmental block is

accompanied by a dramatic decrease in total thymic cellularity, an increase in apoptosis,

and a reduction of pT? expression. These developmentally arrested thymocytes exhibit

increased proliferation in vivo and dramatic expansion ex vivo in response to IL-7

signaling. Our findings suggest that E2A and HEB are not only critical for the regulation

of T cell differentiation but are also necessary to retain developing thymocytes in cell

cycle arrest prior to pre-TCR expression. Together, these results imply that E proteins

are required to coordinate thymocyte differentiation and proliferation.

Bibliographical Information:

Advisor:Zhuang,Yuan; Krangel, Michael; Kelsoe, Garnett; Zhang, Weiguo; Shieh, Tao

School:Duke University

School Location:USA - North Carolina

Source Type:Master's Thesis

Keywords:e2a heb t cell development transcription factor


Date of Publication:05/10/2007

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