Rationale:: Endothelial Notch signaling is critical for early vascular development and survival. Yet, previously described mice lacking endothelial a disintegrin and metalloproteinase 10 (ADAM10), a key regulator of Notch signaling, survived into adulthood with organ-specific vascular defects. These findings raised questions about whether these vascular defects were related to Notch signaling or other functions of ADAM10. Objective:: The aims of the study are to determine whether compensatory or redundant functions of ADAM17 in Notch signaling can explain the survival of Adam10 ΔEC mice, explore the contribution of different Tie2-Cre transgenes to the differences in survival, and establish whether the Adam10 ΔEC vascular phenotypes can be recapitulated by inactivation of Notch receptors in endothelial cells. Methods and Results:: Mice lacking ADAM10 and ADAM17 in endothelial cells ( Adam10/Adam17 ΔEC), which survived postnatally with organ-specific vascular defects, resembled Adam10 ΔEC mice. In contrast, Adam10 ΔEC mice generated with the Tie2Cre transgene previously used to inactivate endothelial Notch ( Adam10 ΔEC ^Flv ) died by E10.5. Quantitative polymerase chain reaction analysis demonstrated that Cre-mediated recombination occurs earlier in Adam10 ΔEC ^Flv mice than in the previously described Adam10 ΔEC mice. Finally, mice lacking endothelial Notch1 ( Notch1 ΔEC) share some organ-specific vascular defects with Adam10 ΔEC mice, whereas Notch4 ^−/− mice lacking endothelial Notch1 ( Notch1 ΔEC /Notch4 ^−/− ) had defects in all vascular beds affected in Adam10 ΔEC mice. Conclusions:: Our results argue against a major role for ADAM17 in endothelial Notch signaling and clarify the difference in phenotypes of previously described mice lacking ADAM10 or Notch in endothelial cells. Most notably, these findings uncover new roles for Notch signaling in the development of organ-specific vascular beds.

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