Development of the larval lymphatic system in zebrafish

Consensus guidelines for the use and interpretation of angiogenesis assays

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference.

Zebrafish mutants and TEAD reporters reveal essential functions for Yap and Taz in posterior cardinal vein development

As effectors of the Hippo signaling cascade, YAP1 and TAZ are transcriptional regulators playing important roles in development, tissue homeostasis and cancer. A number of different cues, including mechanotransduction of extracellular stimuli, adhesion molecules, oncogenic signaling and metabolism modulate YAP1/TAZ nucleo-cytoplasmic shuttling. In the nucleus, YAP1/TAZ tether with the DNA binding proteins TEADs, to activate the expression of target genes that regulate proliferation, migration, cell plasticity, and cell fate. Based on responsive elements present in the human and zebrafish promoters of the YAP1/TAZ target gene CTGF, we established zebrafish fluorescent transgenic reporter lines of Yap1/Taz activity. These reporter lines provide an in vivo view of Yap1/Taz activity during development and adulthood at the whole organism level. Transgene expression was detected in many larval tissues including the otic vesicles, heart, pharyngeal arches, muscles and brain and is prominent in endothelial cells. Analysis of vascular development in yap1/taz zebrafish mutants revealed specific defects in posterior cardinal vein (PCV) formation, with altered expression of arterial/venous markers. The overactivation of Yap1/Taz in endothelial cells was sufficient to promote an aberrant vessel sprouting phenotype. Our findings confirm and extend the emerging role of Yap1/Taz in vascular development including angiogenesis.

Visualization and Tools for Analysis of Zebrafish Lymphatic Development

The accessibility and optical transparency of the zebrafish embryo offers a unique platform for live-imaging of developmental lymphangiogenesis. Transgenic lines labelling lymphatic progenitors and vessels enable researchers to visualize cellular processes and ask how they contribute to lymphatic development in genetic models. Furthermore, validated immunofluorescence staining for key signaling and cell fate markers (phosphorylated Erk and Prox1) allow single cell resolution studies of lymphatic differentiation. Here, we describe in detail how zebrafish embryos and larvae can be mounted for high resolution, staged imaging of lymphatic networks, how lymphangiogenesis can be reliably quantified and how immunofluorescence can reveal lymphatic signaling and differentiation. These methods offer researchers the opportunity to experimentally dissect developmental lymphangiogenesis with outstanding resolution.

Characterization of Zebrafish Facial Lymphatics

Zebrafish are well-established as a model of vascular development. The genetic tractability, external development, permeability to small molecules and optical transparency of zebrafish larvae are all attributes that make this model attractive to the vascular biologist. There are an increasing number of lymphatic reporter lines that enable the visualization of zebrafish lymphatic vessel growth in vivo; these tools, coupled with either forward or reverse genetics, have provided new insights into the process of lymphatic specification and development. Zebrafish larvae have three main lymphatic networks: the trunk lymphatics, the intestinal lymphatics, and the facial lymphatics and it is therefore possible to use zebrafish to determine network-specific roles for molecules implicated in lymphatic development. This chapter provides protocols for visualization and analysis of facial lymphatic development in the zebrafish and may be applied in developmental or drug discovery studies.

A novel perivascular cell population in the zebrafish brain

The blood-brain barrier is essential for the proper homeostasis and function of the CNS, but its mechanism of function is poorly understood. Perivascular cells surrounding brain blood vessels are thought to be important for blood-brain barrier establishment, but their roles are not well defined. Here, we describe a novel perivascular cell population closely associated with blood vessels on the zebrafish brain. Based on similarities in their morphology, location, and scavenger behavior, these cells appear to be the zebrafish equivalent of cells variably characterized as Fluorescent Granular Perithelial cells (FGPs), perivascular macrophages, or 'Mato Cells' in mammals. Despite their macrophage-like morphology and perivascular location, zebrafish FGPs appear molecularly most similar to lymphatic endothelium, and our imaging studies suggest that these cells emerge by differentiation from endothelium of the optic choroidal vascular plexus. Our findings provide the first report of a perivascular cell population in the brain derived from vascular endothelium.