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Paper text:
the following strains were maintained in accord with iacuc approved procedures : ab * , tg(top : gfp ) , tg(-6.0itga2b : egfp ) , tg(hsp70l : gal4 ) , tg(uas : myc - notch1a - intra ) , tg(tp1-mmhbb : egfp ) , tg(tp1-mmhbb : kaede ) , tg(cmyb : egfp ) , tg(kdrl : rfp ) , and dlc . probes and mrna were synthesized from published constructs or cloned de novo according to standard procedures .
5 ng w16mo1 aggttagttctgtcacccacctgtc , w16mo2 gcgtggaatacttacatccaacttc , w16como acgttagttgtgtcagccagctctc . performed by standard methods using primers and conditions described in the complete methods .
the following strains were maintained in accord with iacuc approved procedures : ab * , tg(top : gfp ) , tg(-6.0itga2b : egfp ) , tg(hsp70l : gal4 ) , tg(uas : myc - notch1a - intra ) , tg(tp1-mmhbb : egfp ) , tg(tp1-mmhbb : kaede ) , tg(cmyb : egfp ) , tg(kdrl : rfp ) , and dlc .
probes and mrna were synthesized from published constructs or cloned de novo according to standard procedures .
haematopoietic stem cells ( hscs ) are a self - renewing population that continuously replenish all blood and immune cells during the lifetime of an individual1 , 2 . 
 hscs are used clinically to treat a wide array of diseases , including acute leukaemias and congenital blood disorders , but obtaining suitable numbers of cells and finding immune compatible donors remain serious problems . 
 these concerns have led to an interest in the conversion of embryonic stem cells or induced pluripotent stem cells into hscs , which is not possible using current methodologies . to accomplish this goal , it is critical to understand the native mechanisms involved in specification of hscs during embryonic development . 
 here we demonstrate that wnt16 controls a novel genetic regulatory network required for hsc specification . 
 non - canonical signaling by wnt16 is required for somitic expression of the notch ligands deltac ( dlc ) and deltad ( dld ) , and these ligands are in turn required for establishment of definitive haematopoiesis . 
 notch signalling downstream of dlc / dld is earlier than , and distinct from known cell - autonomous requirements for notch , strongly suggesting that novel notch - dependent relay signal(s ) induce the first hscs in parallel to other established pathways . 
 our results demonstrate that somite - specific gene expression is required for the production of haemogenic endothelium .