Landmarks in the first hundred years of primary (9+0) cilium research.

Primary cilia have had a long research history since 1898, but only in the last few years have investigations become intense. Only a few people took an interest in them until recently, when the consequences of their agenesis or dysfunction suddenly became apparent to all. Their function changed overnight from being speculative to being fully "acknowledged" as sensory, and the consequence of their lacking sensory function(s) led to a bonanza for cell and molecular biologists interested in the impact on clinical disease and disorder. Furthermore, once the medical profession had insight not just into the etiology of an extremely rare syndrome (situs inversus), but into one as prevalent as polycystic kidney disease, furious research activity sprang up in numerous centres, symposium were convened, special sessions arranged, and topical reviews written in all sorts of journals. Without an understanding of the history of research about this organelle, many reviews gave little credit to those who had persevered earlier to make key advances in primary cilium research, and most ignore the wealth of information on them that has relevance to fundamental (cell) biology as well as to medicine. Some of the "landmarks" presented here will hopefully provide a little guidance and a better perspective.