Publications

Bcl11b is a T-cell specific gene in hematopoiesis that begins expression during T-lineage commitment and is required for this process. Aberrant expression of BCL11B or proto-oncogene translocation to the vicinity of BCL11B can be a contributing factor in human T-ALL. To identify the mechanism that controls its distinctive T-lineage expression, we corrected the identified Bcl11b transcription start site and mapped a cell-type-specific differentially methylated region bracketing the Bcl11b promoter. We identified a 1.9-kb region 850 kb downstream of Bcl11b, "Major Peak," distinguished by its dynamic histone marking pattern in development that mirrors the pattern at the Bcl11b promoter. Looping interactions between promoter-proximal elements including the differentially methylated region and downstream elements in the Major Peak are required to recapitulate the T-cell specific expression of Bcl11b in stable reporter assays. Functional dissection of the Major Peak sequence showed distinct subregions, in which TCF-1 sites and a conserved element were required for T-lineage-specific activation and silencing in non-T cells. A bacterial artificial chromosome encompassing the full Bcl11b gene still required the addition of the Major Peak to exhibit T-cell specific expression. Thus, promoter-proximal and Major Peak sequences are cis-regulatory elements that interact over 850 kb to control expression of Bcl11b in hematopoietic cells.

Traumatic brain injury (TBI) elicits innate inflammatory responses that can lead to secondary brain injury. To better understand the mechanisms involved in TBI-induced inflammation, we examined the nature of macrophages responding to TBI in mice. In this model, brain macrophages were increased >20-fold the day after injury and >77-fold 4 days after injury in the ipsilateral hemisphere compared with sham controls. TBI macrophage subsets were identified by using a reporter mouse strain (YARG) that expresses eYFP from an internal ribosome entry site (IRES) inserted at the 3' end of the gene for arginase-1 (Arg1), a hallmark of alternatively activated (M2) macrophages. One day after TBI, 21 ± 1.5% of ipsilateral brain macrophages expressed relatively high levels of Arg1 as detected by yellow fluorescent protein, and this subpopulation declined thereafter. Arg1(+) cells localized with macrophages near the TBI lesion. Gene expression analysis of sorted Arg1(+) and Arg1(-) brain macrophages revealed that both populations had profiles that included features of conventional M2 macrophages and classically activated (M1) macrophages. The Arg1(+) cells differed from Arg1(-) cells in multiple aspects, most notably in their chemokine repertoires. Thus, the macrophage response to TBI initially involves heterogeneous polarization toward at least two major subsets.