Developmentally Programmed Rearrangement of T Cell Receptor Vγ Genes Is Controlled by Sequences Immediately Upstream of the Vγ Genes

AbstractDistinct subsets of γδ T cells expressing different Vγ and Vδ chains arise in ordered waves during thymic development. In the murine Jγ1–Cγ1 cluster, the Vγ3 gene segment is utilized earliest in fetal thymic development, in progenitors of dendritic epidermal T cells (DECs). The Vγ2 gene segment predominates in the late fetal stages and beyond, in cells destined for the secondary lymphoid organs. Using transgenic TCRγ recombination substrates, we demonstrate that this restricted Vγ gene usage is determined by developmentally targeted gene rearrangement. We show that sequences immediately upstream of the Vγ2 and Vγ3 genes direct the rearrangement pattern in adult thymocytes. Thus, the choice of Vγ gene for recombination is coordinated with distinct differentiation programs in γδ subsets

A Novel Element Upstream of the Vγ2 Gene in the Murine T Cell Receptor γ Locus Cooperates with the 3′ Enhancer to Act as a Locus Control Region

Transgenic expression constructs were employed to identify a cis-acting transcription element in the T cell receptor (TCR)-γ locus, called HsA, between the Vγ5 and Vγ2 genes. In constructs lacking the previously defined enhancer (3′ECγ1), HsA supports transcription in mature but not immature T cells in a largely position-independent fashion. 3′ECγ1, without HsA, supports transcription in immature and mature T cells but is subject to severe position effects. Together, the two elements support expression in immature and mature T cells in a copy number–dependent, position-independent fashion. Furthermore, HsA was necessary for consistent rearrangement of transgenic recombination substrates. These data suggest that HsA provides chromatin-opening activity and, together with 3′ECγ1, constitutes a T cell–specific locus control region for the TCR-γ locus

Comparative Study of Hematopoietic Differentiation between Human Embryonic Stem Cell Lines

Directed differentiation of human embryonic stem cells (hESCs) into any desired cell type has been hailed as a therapeutic promise to cure many human diseases. However, substantial roadblocks still exist for in vitro differentiation of hESCs into distinct cell types, including T lymphocytes. Here we examined the hematopoietic differentiation potential of six different hESC lines. We compare their ability to develop into CD34+ or CD34+CD45+ hematopoietic precursor populations under several differentiation conditions. Comparison of lymphoid potential of hESC derived- and fetal tissue derived-hematopoietic precursors was also made. We found diverse hematopoietic potential between hESC lines depending on the culture or passage conditions. In contrast to fetal-derived hematopoietic precursors, none of the CD34+ precursors differentiated from hESCs were able to develop further into T cells. These data underscore the difficulties in the current strategy of hESC forward differentiation and highlight distinct differences between CD34+ hematopoietic precursors generated in vitro versus in vivo