The zebrafish (Danio rerio) is increasingly being used to study basic vertebrate biology and human disease using a rich array of in vivo genetic and molecular tools. However, the inability to readily modify the genome in a targeted fashion has been a bottleneck in the field. Here we show that improvements in artificial transcription activator-like effector nucleases (TALENs) provide a powerful new approach for targeted zebrafish genome editing and functional genomic applications1–5. Using the GoldyTALEN modified scaffold and zebrafish delivery system, we show this enhanced TALEN toolkit demonstrates a high efficiency in inducing locus-specific DNA breaks in somatic and germline tissues. At some loci, this efficacy approaches 100%, including biallelic conversion in somatic tissues that mimics phenotypes seen using morpholino (MO)-based targeted gene knockdowns6. With this updated TALEN system, we successfully used single-stranded DNA (ssDNA) oligonucleotides (oligos) to precisely modify sequences at predefined locations in the zebrafish genome through homology-directed repair (HDR), including the introduction of a custom-designed EcoRV site and a modified loxP (mloxP) sequence into somatic tissue in vivo. We further show successful germline transmission of both EcoRV and mloxP engineered chromosomes. This combined approach offers the potential to model genetic variation as well as to generate targeted conditional alleles.

SummaryKupffer's vesicle is a ciliated organ of asymmetry in the zebrafish embryo that initiates left-right development of the brain, heart and gut Research article Development 1248However, genes implicated in ciliated node cell function are also expressed in non-node cells, and mutations of these genes give rise to a variety of laterality phenotypes and more pleiotropic phenotypes, making it impossible to exclude other mechanisms for LR development during early embryogenesis (for reviews, see Tabin and Vogan, 2003;Wagner and Yost, 2000;Yost, 2003). Furthermore, it is not known whether nodal flow is a murine-specific mechanism. Cilia formation and expression of lrd homologues have recently been observed in structures analogous to the node in chick, frog (Xenopus laevis) and zebrafish embryos (Essner et al., 2002), but the existence of motile cilia and nodal flow has not been demonstrated in non-murine embryos. Further confounding the issue, there are molecular asymmetries that precede the appearance of lrd expression and monocilia in Xenopus Levin et al., 2002) and perhaps in chick (Levin et al., 1995;Stern et al., 1995). This raises the issue of whether ciliated cells in other vertebrate embryos generate fluid flow and have a conserved function for ciliogenesis genes in LR development. In zebrafish, ciliated cells arise in the tailbud at the end of gastrulation (Essner et al., 2002) in a transient spherical organ called Kupffer's vesicle (KV). KV, first described in 1868 (Kupffer, 1868), is a conserved structure among teleost fishes. Electron microscopy studies in the bait fish Fundulus heteroclitus have shown that a single cilium (i.e. monocilium) protrudes from each cell lining KV into the lumen (Brummett and Dumont, 1978). In zebrafish, KV is formed from a group of approximately two-dozen cells, known as dorsal forerunner cells (DFCs), that migrate at the leading edge of the embryonic shield (the zebrafish equivalent of the mouse node) during gastrulation. In contrast to other cells in this region, DFCs do not involute during gastrulation, but remain at the leading edge of epibolic movements. At the end of gastrulation, DFCs migrate deep into the embryo and organize to form KV (Cooper and D'Amico, 1996; D'Amico and Cooper, 1997;Melby et al., 1996). During subsequent somite stages, KV is found ventral to the forming notochord in the tailbud and adjacent to the yolk cell. Although KV was first described well over 100 years ago, it remains unknown whether DFCs and KV are mesodermal or endodermal in origin, and it is unclear what role they play during development, leading to the categorization of KV as an embryonic 'organ of ambiguity ' (Warga and Stainier, 2002).Recently, using a novel technique to knockdown gene expression specifically in DFCs, we reported the first evidence that DFCs and/or KV function in LR patterning (Amack and Yost, 2004). Here, we show that cilia that arise inside KV are motile and generate a consistent counterclockwise fluid flow. A combination of laser ablations, embryological manipul...

Chemokines and chemokine receptors have been posited to have important roles in several common malignancies, including breast and lung cancer. Here, we demonstrate that CXCR7 (RDC1, CCX-CKR2), recently deorphanized as a chemokine receptor that binds chemokines CXCL11 and CXCL12, can regulate these two common malignancies. Using a combination of overexpression and RNA interference, we establish that CXCR7 promotes growth of tumors formed from breast and lung cancer cells and enhances experimental lung metastases in immunodeficient as well as immunocompetent mouse models of cancer. These effects did not depend on expression of the related receptor CXCR4. Furthermore, immunohistochemistry of primary human tumor tissue demonstrates extensive CXCR7 expression in human breast and lung cancers, where it is highly expressed on a majority of tumor-associated blood vessels and malignant cells but not expressed on normal vasculature. In addition, a critical role for CXCR7 in vascular formation and angiogenesis during development is demonstrated by using morpholino-mediated knockdown of CXCR7 in zebrafish. Taken together, these data suggest that CXCR7 has key functions in promoting tumor development and progression.angiogenesis ͉ cancer ͉ chemokine