Blood vessel networks expand in a 2-step process that begins with vessel sprouting and is followed by vessel anastomosis. Vessel sprouting is induced by chemotactic gradients of the vascular endothelial growth factor (VEGF), which stimulates tip cell protrusion. Yet it is not known which factors promote the fusion of neighboring tip cells to add new circuits to the existing vessel network. By combining the analysis of mouse mutants defective in macrophage development or VEGF signaling with live imaging in zebrafish, we now show that macrophages promote tip cell fusion downstream of VEGF-mediated tip cell induction. Macrophages therefore play a hitherto unidentified and unexpected role as vascular fusion cells. Moreover, we show that there are striking molecular similarities between the pro-angiogenic tissue macrophages essential for vascular development and those that promote the angiogenic switch in cancer, including the expression of the cell-surface proteins TIE2 and NRP1. Our findings suggest that tissue macrophages are a target for antiangiogenic therapies, but that they could equally well be exploited to stimulate tissue vascularization in ischemic disease. (Blood. 2010;116(5): 829-840) IntroductionBlood vessels are essential for tissue homeostasis in all vertebrates, and new vessel growth, termed neo-angiogenesis, is therefore a critical process in wound repair to counter tissue ischemia. Undesirably, neo-angiogenesis also promotes the expansion of tumors. Moreover, nonproductive neo-angiogenesis, which fails to restore oxygenation of ischemic tissues, promotes disease progression in, for example, diabetic retinopathy. Much current research is therefore focused on the identification of molecular and cellular targets for either pro-or antiangiogenic therapies. We previously elucidated the mechanism by which alternative splice forms of the vascular endothelial growth factor (VEGF) cooperate to promote blood vessel growth. 1,2 This work led to the current model of angiogenesis, in which blood vessel endothelium specializes into tip and stalk cells to promote vascular network expansion by sprouting growth. While the stalk cells form a lumen to transport blood, the tip cells extend filopodia to detect chemotactic growth factor gradients, which are formed by a combination of VEGF isoforms with a differential affinity for the extracellular matrix. Cooperating with VEGF, notch-delta signaling controls the balance of tip versus stalk cell specialization. 3 Even though much progress has been made in elucidating the mechanism of vascular sprout induction and guidance, a fundamental yet unanswered problem is which mechanism promotes the fusion of nascent vessel sprouts to add new circuits to the existing plexus.Macrophages promote pathologic angiogenesis in several diseases. Thus, circulating bone marrow-derived cells differentiate into proangiogenic cells with macrophage characteristics at adult sites of VEGF expression 4 and are recruited to growing tumors to promote tumor vascularization and therefore progression....

Vertebrate gastrulation involves the specification and coordinated movement of large populations of cells that give rise to the ectodermal, mesodermal and endodermal germ layers. Although many of the genes involved in the specification of cell identity during this process have been identified, little is known of the genes that coordinate cell movement. Here we show that the zebrafish silberblick (slb) locus encodes Wnt11 and that Slb/Wnt11 activity is required for cells to undergo correct convergent extension movements during gastrulation. In the absence of Slb/Wnt11 function, abnormal extension of axial tissue results in cyclopia and other midline defects in the head. The requirement for Slb/Wnt11 is cell non-autonomous, and our results indicate that the correct extension of axial tissue is at least partly dependent on medio-lateral cell intercalation in paraxial tissue. We also show that the slb phenotype is rescued by a truncated form of Dishevelled that does not signal through the canonical Wnt pathway, suggesting that, as in flies, Wnt signalling might mediate morphogenetic events through a divergent signal transduction cascade. Our results provide genetic and experimental evidence that Wnt activity in lateral tissues has a crucial role in driving the convergent extension movements underlying vertebrate gastrulation.

The tremendous complexity of the adult forebrain makes it a challenging task to elucidate how this structure forms during embryonic development. Nevertheless, we are beginning to understand how a simple epithelial sheet of ectoderm gives rise to the labyrinthine network of cells that constitutes the functional forebrain. Here, we discuss early events in forebrain development--those that lead to the establishment of the anterior neural plate and the regional subdivision of this territory into the different domains of the prospective forebrain.

Although manganese is an essential trace metal, little is known about its transport and homeostatic regulation. Here we have identified a cohort of patients with a novel autosomal recessive manganese transporter defect caused by mutations in SLC39A14. Excessive accumulation of manganese in these patients results in rapidly progressive childhood-onset parkinsonism–dystonia with distinctive brain magnetic resonance imaging appearances and neurodegenerative features on post-mortem examination. We show that mutations in SLC39A14 impair manganese transport in vitro and lead to manganese dyshomeostasis and altered locomotor activity in zebrafish with CRISPR-induced slc39a14 null mutations. Chelation with disodium calcium edetate lowers blood manganese levels in patients and can lead to striking clinical improvement. Our results demonstrate that SLC39A14 functions as a pivotal manganese transporter in vertebrates.