Constitutive expression of the pre-TCR enables development of mature T cells.

Expression and signalling through the pre-TCR and the TCRalphabeta resemble two critical checkpoints during T cell development. We investigated to which extent a pre-TCR can functionally replace mature TCRalpha chains during T cell development. For this purpose, transgenic mice were generated expressing the pre-TCRalpha (pTalpha) under the transcriptional control of TCRbeta regulatory elements.

Gimap4 accelerates T-cell death.

Gimap4, a member of the newly identified GTPase of the immunity-associated protein family (Gimap), is strongly induced by the pre-T-cell receptor in precursor T lymphocytes, transiently shut off in double-positive thymocytes, and reappears after TCR-mediated positive selection. Here, we show that Gimap4 remains expressed constitutively in the cytosol of mature T cells. A C-terminal IQ domain binds calmodulin in the absence of calcium, and conserved PKC phosphorylation motifs are targets of concanavalin A (ConA)- or PMA/ionomycin-induced PKC activation.

DNA double-strand breaks in immunoglobulin genes undergoing somatic hypermutation.

How rearranged immunoglobulin (Ig) genes are further diversified by somatic hypermutation is unknown. Using VDJ passenger Ig heavy chain (IgH) knockin mouse strains, we now demonstrate a high frequency of DNA double-strand breaks (DSBs) in the targeted VDJ passenger gene of germinal center (GC) B cells. These DSBs parallel the distribution of mutations in the targeted hypermutation domain and are found preferentially at RGYW motifs, the intrinsic hot spots of somatic hypermutation.

PIM1 reconstitutes thymus cellularity in interleukin 7- and common gamma chain-mutant mice and permits thymocyte maturation in Rag- but not CD3gamma-deficient mice.

The majority of lymphomas induced in Rag-deficient mice by Moloney murine leukemia virus (MoMuLV) infection express the CD4 and/or CD8 markers, indicating that proviral insertions cause activation of genes affecting the development from CD4(-)8(-) pro-T cells into CD4(+)8(+) pre-T cells. Similar to MoMuLV wild-type tumors, 50% of CD4(+)8(+) Rag-deficient tumors carry a provirus near the Pim1 protooncogene. To study the function of PIM proteins in T cell development in a more controlled setting, a Pim1 transgene was crossed into mice deficient in either cytokine or T cell receptor (TCR) signal transduction pathways.

New COP1-binding motifs involved in ER retrieval.

Coatomer-mediated sorting of proteins is based on the physical interaction between coatomer (COP1) and targeting motifs found in the cytoplasmic domains of membrane proteins. For example, binding of COP1 to dilysine (KKXX) motifs induces specific retrieval of tagged proteins from the Golgi back to the endoplasmic reticulum (ER). Making use of the two-hybrid system, we characterized a new sequence (deltaL) which interacts specifically with the delta-COP subunit of the COP1 complex.