|The Allied Genetics Conference (TAGC) Meeting Report|
TAGC brought together seven research communities under one roof.
Authors: Joan Heath and Rebecca D. Burdine
The Allied Genetics Conference (TAGC) took place July 13-17, 2016 in Orlando, Florida. TAGC brought seven research communities together to hold their individual community meetings in one large conference venue. The goal was to promote interactions between communities, and highlight the importance of model organism research in understanding human health and development. To foster interactions, joint plenary sessions were held with keynote speakers representing each community. The 12th International Conference on Zebrafish Development and Genetics was held as part of this larger meeting.
One highlight of the meeting was Didier Stainier (Max Planck Institute for Heart and Lung Research) bringing to a close the long, arduous struggle to clone one of the first zebrafish mutants to be described: cloche. The fascinating aspect of cloche is that its embryos are bloodless and also lack vasculature, meaning that it plays a very early role in the diversification of the early mesoderm into endothelial and haematopoietic tissue fates.
It was recognised long ago that the cloche locus occupied a position very close to the distal tip of the telomere on chromosome 13. This region on the zebrafish genome is poorly assembled and greatly complicated efforts to identify the underlying gene by classical positional cloning. The pursuit of this locus became a holy grail for several groups.
The approach taken by the Stainier laboratory provides further evidence of the power conferred by the advent of CRISPR/Cas9 technology. The researchers reasoned that cloche must be expressed prior to gastrulation and so carried out RNA-seq on individual wild-type and cloche mutant embryos at 6-10 hours post fertilization to identify significantly down-regulated genes. Having identified 19 candidates, 18 gave no phenotype upon mutation using CRISPR. Knocking out the final candidate to be tested, npas4-like (npas4l), phenocopied the mutant. This gene encodes a member of the bHLH-PAS family of transcription factors and directly regulates the etv and tal1 genes, the earliest expressed endothelial and haematopoietic transcription factor genes identified so far. The identification of cloche/npas41 as a master regulator of endothelial and haematopoietic fate may lead to improved protocols for the generation of endothelia and haematopoietic cells in vivo. An article corresponding to this presentation was published in Nature on the same day as the presentation (Reischauer et al. 2016).
Marnie Halpern and Len Zon present Didier Stainier with an award for the cloning of cloche.
Many talks and posters highlighted the use of zebrafish as disease models. Craig Ceol (University of Massachusetts Medical School) showed that Gdf6 expression is upregulated in melanoma, and plays a role in maintaining their neural crest cell identity, which is key to their malignant behavior. Marcel den Hoed (Uppsala University) presented a zebrafish model of atherosclerosis and demonstrated that Flt1 protects vasculature in the larvae from lipid deposits. Steve Farber (Carnegie Institution for Science) introduced new tools for studying high cholesterol levels. Tom Carney (IMCB A*STAR) presented work where the liver in zebrafish is “humanized” by expressing human detoxification enzymes in this organ. This allows zebrafish to be used to more accurately assess toxicity of compounds on the human organ.
Other highlights included: Jessica Nelson (University of Pennsylvania) revealed an unexpected role of huntingtin protein in learning. Shinsuke Seki (Tokyo University of Marine Science and Technology) used medaka spermatogonia to produce oocytes and sperm when transplanted; it may work for zebrafish too! Ashley Bruce (University of Toronto) showed that yolk syncytial layer (YSL) nuclei move through the microtubule network to drive epiboly (vegetal movement of the blastoderm and the YSL to enclose the yolk cell). It was previously thought to be driven by depolymerisation of the network. Chase Bryan (University of Utah) produced some amazing movies of optic cup morphogenesis. Xuefei Yuan (The Hospital for Sick Children) gave a great talk finding noncoding regions that drive expression in cardiac precursors. Yahui Lan (Weill Cornell Medical College) showed that zebrafish tet2/3 mutants have a loss of epicardial migration and proliferation, and highlighted the role of DNA methylation in the process. Aaron Savage (University of Sheffield) used tissue-specific expression of NLS-Cas9 for tissue specific knockouts by injecting sgRNA. Autumn Marsden (University of Iowa) showed that the EF-hand domain in Naked Cuticle (Nkd) is not required for canonical Wnt inhibition, but is required for Wnt-PCP. Tamara Stawicki (University of Washington) showed that intraflagellar transport genes are important in lateral cell line hair cell resistance to neomycin. Rob Cornell (University of Iowa) analysed the periderm, derived from the outermost enveloping layer (EVL), to find genes involved in oral-facial clefting.
In his plenary lecture, Len Zon (HHMI/Children’s Hospital Boston) showcased the value of the zebrafish as an animal model for human disease. Based on live imaging of transgenic zebrafish lines, Zon unveiled a spectacular animation demonstrating how endothelial cells positioned in a specialized region on the ventral wall of the dorsal aorta, the hemogenic endothelium, attain hematopoietic potential through a process known as the endothelial-to-hematopoietic transition (EHT). He described how 21 hematopoietic stem cells (HSCs) bud off the aorta prior to migrating into the subaortic space. Nascent HSCs then enter the circulation to begin their journey to their intermediate stem cell niche in the caudal hematopoietic tissue (CHT), equivalent to the mammalian fetal liver. After a transient proliferation phase, definitive HSCs re-enter the circulation and make their way to the final hematopoietic site, which is the kidney marrow in zebrafish (the bone marrow in mammals). From here, they produce a lifetime supply of mature blood cells.
To highlight the role of zebrafish as a disease model, Zon turned to the severe and rare congenital disease known as Diamond Blackfan anemia. His laboratory had previously identified that zebrafish harboring mutations in the rps29 gene recapitulate many of the hallmarks of this disease, namely red blood cell defects and increased apoptosis in the head. In the latest study, he discussed how a chemical screen identified how calmodulin inhibitors such as trifluoroperizine (TFP) could rescue the paucity of hemoglobin in rps29-deficient embryos. Experiments with the drug in mouse and in vitro human models of Diamond-Blackfan anemia were also successful, and a clinical trial is slated to begin in 2017.
Zebrafish have provided several highly relevant models of melanoma. Zon described HEXIM1 as a new melanoma tumor suppressor that responds to nucleotide stress. HEXIM1 expression is usually low in melanoma and its overexpression in a zebrafish melanoma model suppressed cancer formation, while its inactivation accelerated tumor onset in vivo. Knockdown of HEXIM1 rescued zebrafish neural crest defects and human melanoma proliferation defects that arise from nucleotide depletion. From there the Zon group study revealed that HEXIM1 plays an important role in inhibiting cancer cell-specific gene transcription while also facilitating anti-cancer gene expression.
Highlights from the entire TAGC meeting were published in the December issue of G3 (http://www.g3journal.org/content/6/12/3765.full) and includes additional coverage of Len Zon’s plenary talk. The zebrafish highlights were written primarily by organizer Joan Heath (Walter and Eliza Hall Institute of Medical Research, Australia), and parts are reproduced here with permission from G3. Videos of presentations given at the meeting are also available at http://www.genetics-gsa.org/tagcvideos/.
The organizers for the 12th International Conference on Zebrafish Development and Genetics were:
Rebecca Burdine (Princeton University)
Richard Dorsky (University of Utah)
Joan Heath (Walter and Eliza Hall Institute of Medical Research, Australia)
Anming Meng (Tsinghua University, China)
Teresa Nicholson (Oregon Health and Science University)
Elizabeth Patton (Medical Research Council, Institute of Genetics and Molecular Medicine, UK)
The Organizers for the upcoming 13th International Conference on Zebrafish Development and Genetics in 2018 are:
Miguel Concha (University of Chile)
Yevgenya Grinblat (University of Wisconsin-Madison)
Jill de Jong (University of Chicago)
Kenneth Poss (Duke University)
Sudipto Roy (Institute of Molecular and Cell Biology A*STAR)
Bettina Schmid (Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE))