RSPO3 and plasma cell myeloma: For instance, the interaction of SDC4 and RSPO3 was shown to regulate WNT/planar cell polarity (PCP) signaling during Xenopus gastrulation by a process that requires clathrin-mediated endocytosis (Ohkawara et al., 2011), and SDC1 was shown to promote signaling in multiple myeloma by presenting WNTs and RSPOs (Ren et al., 2018).