The E2A gene encodes for two alternatively spliced proteins, namely E12 and E47, which belong to the family of basic helix-loop-helix transcription factors. The E2A proteins have been characterized extensively as regulators during various stages of B and T lymphocyte development. Recently, we have generated mice deficient for either E12 or E47 and examined their roles in B cell maturation. We show that E47 is essential for developmental progression at the pre-pro- B cell stage, while E12 is dispensable for early B cell development, commitment and maintenance. In contrast, both E12 and E47 play critical roles in pre-B and immature B cells to promote Igλ germline transcription as well as Igλ VJ gene rearrangement. However, it is unclear which molecular mechanisms are used by E12 and E47 to drive lymphocyte development. Thus, the goals of this study are to 1. identify the signalling events that control transcription and splicing of the E2A gene, 2. define individual target genes and interaction partners of E12 and E47 and 3. to examine the distinct functions for E12 and E47 during T cell development. These goals will be accomplished using the previously generated mouse models, lacking either the E12 or E47 protein in combination with cellular and molecular biology approaches. Additionally, the first goal will be approached in cooperation with the applicant’s previous lab, since this lab has extensive experience with the proposed state-of-the-art whole genome Chromatin Immunoprecipitation combined with deep sequencing (ChIP-Seq) approach. Overall, this project will contribute to our understanding of the molecular mechanisms of transcriptional regulation as well as lymphocyte development.