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 Ca2+ flux regulates Kupffer's vesicle development and is required for LR determination. As a basis of Ca2+ flux in many cell types, inositol 1,4,5-trisphosphate (IP3) 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 IP3 signaling in LR determination in Xenopus embryos. Microinjection of an IP3 receptor-function blocking antibody that can inhibit IP3 calcium channel activity randomized the LR axis in terms of left-sided Pitx2 expression and organ laterality. In addition, an IP3 sponge that could inhibit IP3 signaling by binding IP3 more strongly than the IP3 receptor impaired LR determination. Examination of the gastrocoel roof plate revealed that the number of cilia was significantly reduced by IP3 signal blocking. These results provide evidence that IP3 signaling is involved in LR asymmetry formation in vertebrates. (C) 2011 Elsevier Inc. All rights reserved.