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Novel regenerative therapies may stem from deeper understanding of the mechanisms governing cardiovascular lineage diversification. Using enhancer mapping and live imaging in avian embryos, and genetic lineage tracing in mice, we investigated the spatio-temporal dynamics of cardiovascular progenitor populations. We show that expression of the cardiac transcription factor Nkx2.5 marks a mesodermal population outside of the cardiac crescent in the extraembryonic and lateral plate mesoderm, with characteristics of hemogenic angioblasts. Extra-cardiac Nkx2.5 lineage progenitors migrate into the embryo and contribute to clusters of CD41+/CD45+ and RUNX1+ cells in the endocardium, the aorta-gonad-mesonephros region of the dorsal aorta and liver. We also demonstrated that ectopic expression of Nkx2.5 in chick embryos activates the hemoangiogenic gene expression program. Taken together, we identified a hemogenic angioblast cell lineage characterized by transient Nkx2.5 expression that contributes to hemogenic endothelium and endocardium, suggesting a novel role for Nkx2.5 in hemoangiogenic lineage specification and diversification. DOI: http://dx.doi.org/10.7554/eLife.20994.001, eLife digest As an animal embryo develops, it establishes a circulatory system that includes the heart, vessels and blood. Vessels and blood initially form in the yolk sac, a membrane that surrounds the embryo. These yolk sac vessels act as a rudimentary circulatory system, connecting to the heart and blood vessels within the embryo itself. In older embryos, cells in the inner layer of the largest blood vessel (known as the dorsal aorta) generate blood stem cells that give rise to the different types of blood cells. A gene called Nkx2.5 encodes a protein that controls the activity of a number of complex genetic programs and has been long studied as a key player in the development of the heart. Nkx2.5 is essential for forming normal heart muscle cells and for shaping the primitive heart and its surrounding vessels into a working organ. Interfering with the normal activity of the Nkx2.5 gene results in severe defects in blood vessels and the heart. However, many details are missing on the role played by Nkx2.5 in specifying the different cellular components of the circulatory system and heart. Zamir et al. genetically engineered chick and mouse embryos to produce fluorescent markers that could be used to trace the cells that become part of blood vessels and heart. The experiments found that some of the cells that form the blood and vessels in the yolk sac originate from within the membranes surrounding the embryo, outside of the areas previously reported to give rise to the heart. The Nkx2.5 gene is active in these cells for only a short period of time as they migrate toward the heart and dorsal aorta, where they give rise to blood stem cells These findings suggest that Nkx2.5 plays an important role in triggering developmental processes that eventually give rise to blood vessels and blood cells. The next step following on from this work will be to find out what genes the protein encoded by Nkx2.5 regulates to drive these processes. Mapping the genes that control the early origins of blood and blood-forming vessels will help biologists understand this complex and vital tissue system, and develop new treatments for patients with conditions that affect their circulatory system. In the future, this knowledge may also help to engineer synthetic blood and blood products for use in trauma and genetic diseases. DOI: http://dx.doi.org/10.7554/eLife.20994.002

The neural fate commitment of pluripotent stem cells requires the repression of extrinsic inhibitory signals and the activation of intrinsic positive transcription factors. However, how these two events are integrated to ensure appropriate neural conversion remains unclear. In this study, we showed that Pou3f1 is essential for the neural differentiation of mouse embryonic stem cells (ESCs), specifically during the transition from epiblast stem cells (EpiSCs) to neural progenitor cells (NPCs). Chimeric analysis showed that Pou3f1 knockdown leads to a markedly decreased incorporation of ESCs in the neuroectoderm. By contrast, Pou3f1-overexpressing ESC derivatives preferentially contribute to the neuroectoderm. Genome-wide ChIP-seq and RNA-seq analyses indicated that Pou3f1 is an upstream activator of neural lineage genes, and also is a repressor of BMP and Wnt signaling. Our results established that Pou3f1 promotes the neural fate commitment of pluripotent stem cells through a dual role, activating internal neural induction programs and antagonizing extrinsic neural inhibitory signals. DOI: http://dx.doi.org/10.7554/eLife.02224.001, eLife digest After an egg has been fertilized, it undergoes a series of divisions to produce a ball of cells known as a blastocyst. The cells within the blastocyst are pluripotent stem cells, which have the potential to become many different types of cell. After a few days, the stem cells organize into three layers—an innermost layer called the endoderm, a middle layer of mesoderm, and an outer layer of ectoderm—that ultimately give rise to different types of tissues. The brain and nervous system are formed from cells in the neuroectoderm, which is part of the ectoderm. Now, Zhu et al. have shown that a transcription factor called Pou3f1 triggers stem cells within a region of the ectoderm to turn into neural progenitor cells, thereby generating the neuroectoderm. These neural progenitor cells then go on to become neurons and glial cells that make up the brain and nervous system. Using a virus to reduce levels of Pou3f1 in embryonic stem cells grown in a dish led to a drop in the number of stem cells that committed to neural progenitor cells. Overexpressing Pou3f1 in the stem cells restored the number of neural progenitor cells. Together these results showed that Pou3f1 is both necessary and sufficient for the conversion of embryonic stem cells into future neurons and glia. The same result was seen when embryonic stem cells containing either reduced or elevated levels of Pou3f1 were injected into 2.5-day-old mouse blastocysts, which were then implanted into surrogate females. The resulting embryos comprised some cells with normal levels of Pou3f1, and others with either too little or too much. Cells with elevated Pou3f1 mostly became neural progenitors, whereas those with reduced levels rarely did so. Gene expression studies revealed that Pou3f1 promoted the formation of neural progenitor cells by activating the expression of pro-neuronal genes inside the stem cells, and by blocking anti-neuronal pathways called Wnt/BMP signaling cascades initiated outside the cells. By revealing the two roles of Pou3f1, Zhu et al. have increased our understanding of one of the earliest stages of nervous system development. Further work is required to determine exactly how Pou3f1 exerts its effects and, in particular, whether it performs its two roles simultaneously or in sequence. DOI: http://dx.doi.org/10.7554/eLife.02224.002