The Ets family transcription factor PU.1 is essential for the development and maintenance of several hematopoietic lineages. In the thymus, PU.1 is expressed only in the early ETP/DN1, DN2a and DN2b stages of development. While PU.1 deletion in multipotent precursors leads to a complete block in T-cell development its function in the intrathymic stages in which it is expressed remains undetermined. The goal of this expression profiling study was to determine if PU.1 regulates the expression of T-lineage genes during the early stages of development. To do this, we generated the PU.1-Eng construct which expresses a fusion protein containing the DNA binding ETS domain of PU.1 (aas 159-260) fused to the obligate repressor domain (aas 1-298) of the Drosophila engrailed protein. The PU.1-ETS construct only expresses the ETS domain of PU.1 (aas 159-260) and serves as a control. Fetal liver precursors were isolated from e14.5 embryos and co-cultured with OP9-DL1 cells in the presence of IL-7 and Flt3L (5 ng/ml each) for 4 days to obtain FLDN1, DN2a and DN2b cells. These were infected with vector only, PU.1-ETS and the PU.1-Eng constructs and DN2 cells were sorted after 20 hours of infection. Total RNA was isolated from these cells and polyA+ fraction was used to prepare libraries for high throughput sequencing. Libraries prepared from 2 independent sets of samples were subjected to non-strand specific single-end sequencing. Overall design: Two sets of samples generated from fetal liver precursor derived DN2 cells expressing PU.1-ETS and PU.1-Eng constructs were used for expression profiling. The LZRS retroviral vector, without any insert, was used to generate the vector control dataset.