Phospholipid signaling

Ten years ago, describing what is new in phospholipid signaling in ten pages of Cell would have been easy; it would have been essentially a summary of the phosphoinositidase C (PIC) story: phosphatidylinositol(4,5)bisphosphate (Ptdlns(4,5)P2) hydrolysis to inositiol(1,4,5)trisphosphate (Ins(1",4,5)P3), with the synergistic action of Ca 2÷ (mobilized by Ins(1,4,5)P3) and diacylglycerol (DAG) on protein kinase C (PKC) (Table 1). As will become obvious below, the involvement of phospholipids in cell signaling is now enormously more complicated, and as more potential signaling systems emerge, it becomes even less clear as to which does what. With many of the systems, we are at a stage of ignorance similar to that in the late 1970's with PIC, confused and uncertain and largely lacking the tools and basic knowledge to build up the picture. So, with the limited space available we can make no attempt at comprehensive coverage, but we will try to summarize, mostly by specific examples, what we see as the crucial questions as things stand now. The preceding sentence should be taken as a plea for tolerance from workers whose papers we have not cited and who consequently feel slighted.