Defining cancer stem cells by xenotransplantation in zebrafish.

The zebrafish (Danio rerio) has become an increasingly utilized and relevant model organism in the study of cancer. The use of transgenic and reverse genetic approaches has yielded several strains that model a variety of human neoplasms. In addition to modeling human disease, these strains provide a platform for the analysis of tumor stem cells. Here we describe the basic technique for the isolation and transplantation of tumor tissue in the zebrafish. This technique was designed to study metastasis and invasive potential of zebrafish tumor cells. Additionally, the basic protocol can be modified in order to describe cancer stem cell characteristics, including proliferative capacity, self-renewal, and the minimum number of tumor cells required for engraftment.

Estrogen defines the dorsal-ventral limit of VEGF regulation to specify the location of the hemogenic endothelial niche.

Genetic control of hematopoietic stem and progenitor cell (HSPC) function is increasingly understood; however, less is known about the interactions specifying the embryonic hematopoietic niche. Here, we report that 17ß-estradiol (E2) influences production of runx1+ HSPCs in the AGM region by antagonizing VEGF signaling and subsequent assignment of hemogenic endothelial (HE) identity. Exposure to exogenous E2 during vascular niche development significantly disrupted flk1+ vessel maturation, ephrinB2+ arterial identity, and specification of scl+ HE by decreasing expression of VEGFAa and downstream arterial Notch-pathway components; heat shock induction of VEGFAa/Notch rescued E2-mediated hematovascular defects. Conversely, repression of endogenous E2 activity increased somitic VEGF expression and vascular target regulation, shifting assignment of arterial/venous fate and HE localization; blocking E2 signaling allowed venous production of scl+/runx1+ cells, independent of arterial identity acquisition. Together, these data suggest that yolk-derived E2 sets the ventral boundary of hemogenic vascular niche specification by antagonizing the dorsal-ventral regulatory limits of VEGF.