Fig. 6

sFlt1 function in endothelial cells can limit venous ISV over-sprouting around the spinal cord.

(A–B’) 82 hpf TgBAC(flt1:YFP);Tg(elavl3:gal4);Tg(UAS:mcherry-NTR) trunks after treatment with DMSO (A and A’) or 2 mM Mtz (B and B’) between 30 and 82 hpf. TgBAC(flt1:YFP) expression is observed strongly in ECs and weakly in cells residing in the spinal cord. Genetic ablation of neurons leads to an almost complete loss of TgBAC(flt1:YFP) expression in the spinal cord (B and B’). Scale bar, 50 µm. (C–C” and D–D”) High magnification single-plane confocal images of 80 hpf TgBAC(flt1:YFP);TgBAC(gfap:gal4ff);Tg(UAS:mcherry-NTR) spinal cord. TgBAC(flt1:YFP) expression does not co-localize with mCherry⁺ radial glia. Yellow dashed circles mark the position of the TgBAC(flt1:YFP)-positive spinal cord cells (C’, C”, D’, and D”). Scale bar, 30 µm. (E) Schematic diagram of the transplantation assay (F–J). Cells taken from TgBAC(etv2:EGFP) flt1^bns29/bns29 or Tg(kdrl:TagBFP) flt1^+/+ donor embryos were transplanted into Tg(kdrl:TagBFP) flt1^+/+ or TgBAC(etv2:EGFP) flt1^bns29/bns29 host embryos, respectively. (F and G) 154 hpf Tg(kdrl:TagBFP) flt1^+/+ trunk vasculature with transplanted cells from TgBAC(etv2:EGFP) flt1^bns29/bns29 embryos. Yellow arrows point to ectopic sprouts from transplanted TgBAC(etv2:EGFP) flt1^bns29/bns29 ECs in the dorsal trunk. Only the transplanted TgBAC(etv2:EGFP) flt1^bns29/bns29 ECs, but not the neighboring Tg(kdrl:TagBFP) flt1^+/+ ECs, exhibit ectopic ISV sprouting. Scale bar, 100 µm. (H and I) 154 hpf TgBAC(etv2:EGFP) flt1^bns29/bns29 trunk vasculature with transplanted cells from Tg(kdrl:TagBFP) flt1^+/+ embryos. White arrows point to transplanted Tg(kdrl:TagBFP) flt1^+/+ ECs in the dorsal trunk, which do not exhibit ectopic sprouting, unlike neighboring TgBAC(etv2:EGFP) flt1^bns29/bns29 ECs that show ectopic sprouting. Scale bar, 100 µm. (J) Percentage of transplanted ISVs in the dorsal trunk that exhibited ectopic sprout(s) at 154 hpf for the experiments shown in panels (F–I).