Bacteriophage P1 Cre/loxP based systems can be used to manipulate the genomes of mice in vivo and in vitro, allowing the generation of tissue‐specific conditional mutants. Wehave generated mouse lines expressing Cre recombinase in hematopoietic tissues using the vav regulatory elements, or in lymphoid cells using the hCD2 promoter and locus control region (LCR). The R26R‐EYFP Cre reporter mouse line was used to determine the pattern of Cre expression in each line and enabled the assessment of Cre activity at a single‐cell level. Analysis showed that the vav promoter elements were able to direct Cre‐mediated recombination in all cells of the hematopoietic system. The hCD2 promoter and LCR on the other hand were able to drive Cre‐mediated recombination only in T cells and B cells, but not in other hematopoietic cell types. Furthermore, in the appropriate tissues, deletion of the floxed target was complete in all cells, thereby excluding the possibility of variegated expression of the Cre transgene. Both of these Cre‐transgenic lines will be useful in generating tissue‐specific gene deletions within all the cells of hematopoietic or lymphoid tissues.

Natural killer (NK) cells are a subset of lymphocytes crucial for innate immunity and modification of adaptive immune responses. In contrast to commitment to the T cell or B cell lineage, little is known about NK cell lineage commitment. Here we show that the basic leucine zipper (bZIP) transcription factor E4BP4 (also called NFIL3) is essential for generation of the NK cell lineage. E4BP4-deficient mice (Nfil3(-/-); called 'E4bp4(-/-)' here) had B cells, T cells and NKT cells but specifically lack NK cells and showed severely impaired NK cell-mediated cytotoxicity. Overexpression of E4bp4 was sufficient to increase NK cell production from hematopoietic progenitor cells. E4BP4 acted in a cell-intrinsic manner 'downstream' of the interleukin 15 receptor (IL-15R) and through the transcription factor Id2. E4bp4(-/-) mice may provide a model for definitive analysis of the contribution of NK cells to immune responses and pathologies.

Decreased autophagy contributes to malignancies; however, it is unclear how autophagy has an impact on tumor growth. Acute myeloid leukemia (AML) is an ideal model to address this as (i) patient samples are easily accessible, (ii) the hematopoietic stem and progenitor cells (HSPC) where transformation occurs is well characterized and (iii) loss of the key autophagy gene Atg7 in HSPCs leads to a lethal pre-leukemic phenotype in mice. Here we demonstrate that loss of Atg5 results in an identical HSPC phenotype as loss of Atg7, confirming a general role for autophagy in HSPC regulation. Compared with more committed/mature hematopoietic cells, healthy human and mouse HSPCs displayed enhanced basal autophagic flux, limiting mitochondrial damage and reactive oxygen species in this long-lived population. Taken together, with our previous findings these data are compatible with autophagy-limiting leukemic transformation. In line with this, autophagy gene losses are found within chromosomal regions that are commonly deleted in human AML. Moreover, human AML blasts showed reduced expression of autophagy genes and displayed decreased autophagic flux with accumulation of unhealthy mitochondria, indicating that deficient autophagy may be beneficial to human AML. Crucially, heterozygous loss of autophagy in an MLL–ENL model of AML led to increased proliferation in vitro, a glycolytic shift and more aggressive leukemias in vivo. With autophagy gene losses also identified in multiple other malignancies, these findings point to low autophagy, providing a general advantage for tumor growth.