In the mouse embryo, the aorta-gonad-mesonephros (AGM) region is considered to be the sole location for intraembryonic emergence of hematopoietic stem cells (HSCs). Here we report that, in parallel to the AGM region, the E10.5-E11.5 mouse head harbors bona fide HSCs, as defined by long-term, high-level, multilineage reconstitution and self-renewal capacity in adult recipients, before HSCs enter the circulation. The presence of hemogenesis in the midgestation head is indicated by the appearance of intravascular cluster cells and the blood-forming capacity of a sorted endothelial cell population. In addition, lineage tracing via an inducible VE-cadherin-Cre transgene demonstrates the hemogenic capacity of head endothelium. Most importantly, a spatially restricted lineage labeling system reveals the physiological contribution of cerebrovascular endothelium to postnatal HSCs and multilineage hematopoiesis. We conclude that the mouse embryonic head is a previously unappreciated site for HSC emergence within the developing embryo.

IMP3 (insulin-like growth factor-2 mRNA binding protein 3) is an oncofetal protein whose expression is prognostic for poor outcome in several cancers. Although IMP3 is expressed preferentially in triple- negative breast cancer (TNBC), its function is poorly understood. We observed that IMP3 expression is significantly higher in tumor initiating than non-tumor initiating breast cancer cells and we demonstrate that IMP3 contributes to self-renewal and tumor initiation, properties associated with cancer stem cells (CSCs). The mechanism by which IMP3 contributes to this phenotype involves its ability to induce the stem cell factor SOX2. IMP3 does not interact with SOX2 mRNA significantly or regulate SOX2 expression directly. We discovered that IMP3 binds avidly to SNAI2 (SLUG) mRNA and regulates its expression by binding to the 5′ UTR. This finding is significant because SLUG has been implicated in breast CSCs and TNBC. Moreover, we show that SOX2 is a transcriptional target of SLUG. These data establish a novel mechanism of breast tumor initiation involving IMP3 and they provide a rationale for its association with aggressive disease and poor outcome.

Critical roles of IL-27 in autoimmune diseases and infections have been reported; however, the contribution of endogenous IL-27 to tumor progression remains elusive. In this study, by using IL-27p28 conditional knockout mice, we demonstrate that IL-27 is critical in protective immune response against methyl-cholanthrene–induced fibrosarcoma and transplanted B16 melanoma, and dendritic cells (DCs) are the primary source. DC-derived IL-27 is required for shaping tumor microenvironment by inducing CXCL-10 expression in myeloid-derived suppressor cells and regulating IL-12 production from DCs, which lead to the recruitment and activation of NK and NKT cells resulting in immunological control of tumors. Indeed, reconstitution of IL-27 or CXCL-10 in tumor site significantly inhibits tumor growth and restores the number and activation of NK and NKT cells. In summary, our study identifies a previous unknown critical role of DC-derived IL-27 in NK and NKT cell–dependent antitumor immunity through shaping tumor microenvironment, and sheds light on developing novel therapeutic approaches based on IL-27.

Tregs (Foxp3CD4) are enriched in tumors to foster a tolerant microenvironment that inhibits antitumor immune response. IL-27 is reported to regulate the development and function of Tregs in vitro and in vivo; however, the effects of endogenous IL-27 on Tregs in the tumor microenvironment remain elusive. We demonstrated that in the absence of DC-derived IL-27, Tregs were decreased significantly in transplanted B16 melanoma, transplanted EL-4 lymphoma, and MCA-induced fibrosarcoma by using IL-27p28 conditional KO mice. Further studies revealed that IL-27 promoted the expression of CCL22, which is established to mediate the recruitment of peripheral Tregs into tumors. Tumor-associated DCs were identified as the major source of CCL22 in tumor sites, and IL-27 could induce CCL22 expression in an IL-27R-dependent manner. Intratumoral reconstitution of rmCCL22 or rmIL-27, but not rmIL-27p28, significantly restored the tumor infiltration of Tregs in IL-27p28 KO mice. Correlated with a decreased number of Tregs, tumor-infiltrating CD4 T cells were found to produce much more IFN-γ in IL-27p28 KO mice, which highlighted the physiological importance of Tregs in suppressing an antitumor immune response. Overall, our results identified a novel mechanism of action of IL-27 on Tregs in the context of cancers.

The integrin α6β4 (referred to as β4) is expressed in epithelial cells where it functions as a laminin receptor. Although in vitro studies have implicated β4 in the biology of mammary epithelial cells, its contribution to mammary gland development has not been settled. To address this problem, we generated and analyzed itgb4flox/flox MMTV-Cre− and itgb4flox/flox MMTV-Cre+ mice. The salient features of embryonic mammary tissue from itgb4flox/flox MMTV-Cre+ mice were significantly smaller mammary buds and increased apoptosis in the surrounding mesenchyme. Also, compared to control glands, the itgb4-deleted mammary buds lacked expression of the progenitor cell marker CK14 and they were unable to generate mammary glands upon transplantation into cleared fat pads of recipient mice. Analysis of mammary glands at puberty and during pregnancy revealed that itgb4-diminished mammary tissue was unable to elongate and undergo branching morphogenesis. Micro-dissection of epithelial cells in the mammary bud and of the surrounding mesenchyme revealed that loss of β4 resulted in a significant decrease in the expression of parathyroid hormone related protein (PTHrP) in epithelial cells and of target genes of the PTHrP receptor in mesenchymal cells. Given that the phenotype of the itgb4-deleted mammary tissue mimicked that of the PTHrP knockout, we hypothesized that β4 contributes to mammary gland development by sustaining PTHrP expression and enabling PTHrP signaling. Indeed, the inability of itgb4-deleted mammary buds to elongate was rescued by exogenous PTHrP. These data implicate a critical role for the β4 integrin in mammary gland development and provide a mechanism for this role.