Hippo signaling is a conserved pathway that controls cell prolifcration, apoptosis (cell death), and organ size in response to cell density. At low cell density (Figure I, on the left), transcription co-activators YAP and TAZ enter the nucleus and induce expression of genes that favor cell growth and proliferation. As cell density increases (figure 2 on the right), interactions between membrane-bound FAT4 receptors and DCHS 1/2 on neighboring cells trigger activation of cytoplasmic kinases Mst l /2 and LATS1/2. These kinases phosphorylate TAZ/YAP and prevent them from entering the nucleus, thereby reducing gene expression. 27. What is the ligand in this pathway? 28. What is the receptor in this pathway? 29. What are the target proteins in this pathway? What type of proteins are these (we've seen these in class during Week 3 )? 30. What happens when the target proteins are phosphorylated? 31. What is the ultimate cellular response if this pathway is activated?.