IP3 signaling is required for cilia formation and left-right body axis determination in Xenopus embryos

Vertebrate left-right (LR) body axis is manifested as an asymmetrical alignment of the internal organs such as the heart and the gut. It has been proposed that the process of LR determination commonly involves a cilia-driven leftward flow in the mammalian node and its equivalents (Kupffer's vesicle in zebrafish and the gastrocoel roof plate in Xenopus). Recently, it was reported that Ca(2+) flux regulates Kupffer's vesicle development and is required for LR determination. As a basis of Ca(2+) flux in many cell types, inositol 1,4,5-trisphosphate (IP(3)) receptor-mediated calcium release from the endoplasmic reticulum (ER) plays important roles. However, its involvement in LR determination is poorly understood. We investigated the role of IP(3) signaling in LR determination in Xenopus embryos. Microinjection of an IP(3) receptor-function blocking antibody that can inhibit IP(3) calcium channel activity randomized the LR axis in terms of left-sided Pitx2 expression and organ laterality. In addition, an IP(3) sponge that could inhibit IP(3) signaling by binding IP(3) more strongly than the IP(3) receptor impaired LR determination. Examination of the gastrocoel roof plate revealed that the number of cilia was significantly reduced by IP(3) signal blocking. These results provide evidence that IP(3) signaling is involved in LR asymmetry formation in vertebrates.