Fig: TUNEL assay in Tg(kdrl:GFP)la116 zebrafish embryos injected with a control morpholino (MO-ctr); with a morpholino against unc5b (MO-unc5b) or co-injected with 50 pg of unc5b-Δ8 mRNA and treated with two different caspase inhibitors (Q-VD-Oph and Z-VAD-FMK). Arrows indicate TUNEL-positive ECs in the trunk region. Scale bar: 100 μm.

 

Fine-tune regulation of apoptotic and antiapoptotic signals contributes to blood vessels homeostasis. We found that endothelial cells (ECs) specifically express an alternative splicing variant of the dependence receptor UNC5B (UNC5B-Δ8) insensitive to the prosurvival Netrin1 signaling. Upon unc5b downregulation in zebrafish embryos we previously described defects in the formation of a vessel structure named PAV. Therefore, we investigated if this defect was caused by an alteration in the apoptotic signal within ECs. We detected apoptotic signaling specifically in zebrafish ECs, from which PAV arises, by means of immunofluorescence analyses and cell death detection tunel assay. We hypothesize that vascular defects observed in unc5b-MO embryos might depend on the reduction of the apoptosis in ECs. Indeed, in unc5b-MO injected embryos in which the PAV is not present, apoptosis in ECs in reduced. Interestingly, unc5b-Δ8 mRNA injection rescues PAV formation restoring the correct balance of apoptosis in ECs. To strength the role of the apoptotic signal in PAV formation, we treated embryos with different inhibitors of apoptosis and, as expected, we did not restore the correct formation of the PAV structure.

 

Pradella, D., Deflorian, G., Pezzotta, A. et al. A ligand-insensitive UNC5B splicing isoform regulates angiogenesis by promoting apoptosis. Nat Commun 12, 4872 (2021). https://doi.org/10.1038/s41467-021-24998-6