In this research project, we have so far obtained the following findings. First, Aspp1 plays an important role in fusion between lymph sacs composed of lymphatic endothelial cells derived from blood endothelial cells in the jugular vein during an initial phase of lymphatic vascular development (unpublished data). Second, Aspp1 plays an important role in the formation of physiological lymph-venous connection sites at the venous angle (unpublished data). Third, in a differentiation culture system from embryonic stem cells into endothelial cells, Aspp1-deficient endothelial cells fail to show a morphological change from a sheet-like cluster into a network of endothelial cells, compared to wild-type endothelial cells (unpublished data). Finally, C-terminal Src Kinase which has been implicated in epithelial morphogenesis by interacting with ASPP in Drosophila plays a role in lymphatic tubular morphogenesis in the mouse (unpublished data).