Stem cells reside in specialized microenvironments or “niches” which regulate their function. In vitro studies employing hypoxic culture conditions (≤ 5% O2) have revealed strong regulatory links between O2 availability and stem/precursor cell functions1–6. Therefore, while some stem cells are perivascular, others may occupy hypoxic niches and be regulated by O2 gradients. However, the underlying mechanisms remain unclear. Here, we show that Hypoxia Inducible Factor-1α (HIF-1α), a principal mediator of hypoxic adaptations, modulates Wnt/β-catenin signalling in hypoxic embryonic stem (ES) cells by enhancing β-catenin activation and expression of downstream effectors LEF-1 and TCF-1. This regulation extends to primary cells, including isolated neural stem cells (NSCs), and is not observed in differentiated cells. In vivo, Wnt/β-catenin activity is closely associated with low O2 regions in the subgranular zone (SGZ) of the hippocampus, a key NSC niche7. Hif-1α deletion impairs hippocampal Wnt-dependent processes, including NSC proliferation, differentiation and neuronal maturation. This decline correlates with reduced Wnt/β-catenin signalling in the SGZ. Therefore, O2 availability may have a direct role in stem cell regulation via HIF-1α modulation of Wnt/β-catenin signalling.

Apicomplexan parasites are the cause of numerous important human diseases including malaria and AIDS-associated opportunistic infections. Drug treatment for these diseases is not satisfactory and is threatened by resistance. The discovery of the apicoplast, a chloroplast-like organelle, presents drug targets unique to these parasites. The apicoplast-localized fatty acid synthesis (FAS II) pathway, a metabolic process fundamentally divergent from the analogous FAS I pathway in humans, represents one such target. However, the specific biological roles of apicoplast FAS II remain elusive. Furthermore, the parasite genome encodes additional and potentially redundant pathways for the synthesis of fatty acids. We have constructed a conditional null mutant of acyl carrier protein, a central component of the FAS II pathway in Toxoplasma gondii. Loss of FAS II severely compromises parasite growth in culture. We show FAS II to be required for the activation of pyruvate dehydrogenase, an important source of the metabolic precursor acetyl-CoA. Interestingly, acyl carrier protein knockout also leads to defects in apicoplast biogenesis and a consequent loss of the organelle. Most importantly, in vivo knockdown of apicoplast FAS II in a mouse model results in cure from a lethal challenge infection. In conclusion, our study demonstrates a direct link between apicoplast FAS II functions and parasite survival and pathogenesis. Our genetic model also offers a platform to dissect the integration of the apicoplast into parasite metabolism, especially its postulated interaction with the mitochondrion. apicomplexa ͉ fatty acid biosynthesis ͉ lipoic acid ͉ Plasmodium ͉ plastid

Dabrafenib was well tolerated and clinically active in patients with BRAF(V600E/K) mut(+) MM. cfDNA may be a useful prognostic and response marker in future studies.

Purpose: Tumor-derived circulating cell-free DNA (cfDNA) is a potential alternative source from which to derive tumor mutation status. cfDNA data from four clinical studies of the BRAF inhibitor (BRAFi) dabrafenib or the MEK inhibitor (MEKi) trametinib were analyzed to determine the association between BRAF mutation status in cfDNA and tumor tissue, and the association of BRAF cfDNA mutation status with baseline factors and clinical outcome.Experimental Design: Patients with BRAF V600 mutationpositive melanoma were enrolled in each study after central confirmation of BRAF status in tumor using a PCR-based assay. BRAF mutation status in cfDNA from patient plasma collected at baseline, 732 of 836 (88%) enrolled patients in total, was determined.Results: BRAF mutations were detectable in cfDNA in 76% and 81% of patients with BRAF V600E/V600K-positive tumors, respectively. Patients negative for BRAF mutations in cfDNA had longer progression-free survival (PFS) and overall survival in each of the four studies, compared with patients with detectable cfDNA BRAF mutations. The presence of BRAFmutant cfDNA was an independent prognostic factor for PFS after multivariate adjustment for baseline factors in three of four studies. Patients negative for BRAF mutation-positive cfDNA in plasma had higher response rates to dabrafenib and trametinib.Conclusions: BRAF mutations in cfDNA are detectable in >75% of late-stage melanoma patients with BRAF mutationpositive tumors. The lack of circulating, BRAF mutation-positive cfDNA is clinically significant for metastatic melanoma patients, and may be a prognostic marker for better disease outcome. Clin Cancer Res; 22(3); 567-74. Ó2015 AACR.