Type 1 and 3 inositol trisphosphate receptors are required for extra-embryonic vascular development

The embryonic-maternal interface of the placental labyrinth, allantois, and yolk sac are vital during embryogenesis; however, the precise mechanism underlying the vascularization of these structures remains unknown. Herein we focus on the role of inositol 1,4,5-trisphosphate (IP₃) receptors (IP₃R), which are intracellular Ca²⁺ release channels, in placentation. Double knockout (DKO) of type 1 and 3 IP₃Rs (IP₃R1 and IP₃R3, respectively) in mice resulted in embryonic lethality around embryonic day (E) 11.5. Because IP₃R1 and IP₃R3 were co-expressed in endothelial cells in the labyrinth, allantois, and yolk sac, we investigated extra-embryonic vascular development in IP₃R1- and IP₃R3-DKO mice. The formation of chorionic plates and yolk sac vessels seemed dysregulated around the timing of the chorio-allantoic attachment, immediately followed by the disorganization of allantoic vessels, the decreased expression of the spongiotrophoblast cell marker Tpbpa and the growth retardation of the embryos in DKO mice. Fluorescent immunohistochemistry demonstrated downregulation of a vascular endothelial marker, CD31, in labyrinth embryonic vessels and poor elongation of extra-embryonic mesoderm into the labyrinth layer in DKO placenta, whereas the branching of the DKO chorionic trophoblast was initiated. In addition, allantoic and yolk sac vessels in extra-embryonic tissues were less remodeled in DKO mice. In vitro endothelial cord formation and migration activities of cultured vascular endothelial cells derived from human umbilical vein were downregulated under the inhibition of IP₃R. Our results suggest that IP₃R1 and IP₃R3 are required for extra-embryonic vascularization in the placenta, allantois, and yolk sac. This is the first demonstration of the essential role of IP₃/IP₃Rs signaling in the development of the vasculature at the embryonic-maternal interface.