Tetraspanin18 regulates angiogenesis through VEGFR2 and Notch pathways.

The VEGF pathway is critically required for vasculogenesis, the formation of the primary vascular network. It is also required for angiogenesis resulting in sprouting and pruning of vessels to generate mature arborizing structures. The Notch pathway is essential for arterial-venous specification and the maturation of nascent vessels. We have determined that Tspan18, a member of the Tetraspanin family, is expressed in developing vessels but not in mature vasculature in zebrafish and mouse wound healing. Moreover, reduction at Tspan18 level resulted in aberrant vascular patterning, impaired vessel stability and defective arterial-venous specification. Tspan18 deficiency reduced VEGF, VEGFR2, Notch3 and EphrinB2, and increased EphB4, VEGFR3, Semaphorin3, Neuropilin and PlexinD1 expression. Furthermore, vascular defects of Tspan18 deficiency could be rescued by ectopic expression of VEGFR2 and Notch, but not by knockdown of Semaphorin or Plexin. Functional studies showed that knockdown of Tspan18 led to reduced endothelial cell migration, invasion and tube formation. Tspan18 has dynamic expression, regulates vascular development and maturation in the embryo with re-expression in adult life in wound healing.

Zebrafish Craniofacial Development: A Window into Early Patterning.

The formation of the face and skull involves a complex series of developmental events mediated by cells derived from the neural crest, endoderm, mesoderm, and ectoderm. Although vertebrates boast an enormous diversity of adult facial morphologies, the fundamental signaling pathways and cellular events that sculpt the nascent craniofacial skeleton in the embryo have proven to be highly conserved from fish to man. The zebrafish Danio rerio, a small freshwater cyprinid fish from eastern India, has served as a popular model of craniofacial development since the 1990s. Unique strengths of the zebrafish model include a simplified skeleton during larval stages, access to rapidly developing embryos for live imaging, and amenability to transgenesis and complex genetics. In this chapter, we describe the anatomy of the zebrafish craniofacial skeleton; its applications as models for the mammalian jaw, middle ear, palate, and cranial sutures; the superior imaging technology available in fish that has provided unprecedented insights into the dynamics of facial morphogenesis; the use of the zebrafish to decipher the genetic underpinnings of craniofacial biology; and finally a glimpse into the most promising future applications of zebrafish craniofacial research.