Intraflagellar transport is the rapid, bidirectional movement of protein complexes along the length of most eukaryotic cilia and flagella. Discovery of this intracellular process in Chlamydomonas reinhardtii 20 years ago led to a rapid discovery of cellular mechanisms that underlie a large number of human ciliopathies. Described herein are the events that led to this discovery. As a graduate student, I thought how strange it must be to look at your own research 20 years later. In my hands was a review titled “Two Decades since the Naming of Tubulin” ( Mohri and Hosoya, 1988 ). I certainly did not imagine at the time that I would ever make a similar retrospective. Yet, here I am, reflecting upon my discovery of intraflagellar transport (IFT) 20 years ago ( Kozminski et al. , 1993b ), in January 1992, when I was a doctoral student with Joel Rosenbaum in Yale's Department of Biology. The Mohri and Hosoya review interested me because my dissertation research initially focused on the functional significance of a tubulin posttranslational modification, acetylation. Studying the biflagellate, unicellular, green alga Chlamydomonas reinhardtii , I asked whether alterations in the amount of acetylated α-tubulin affected the stability or function of the flagellar axoneme, the microtubule core of the flagellum. I found no mutant phenotype, making for a quick but publishable end to my nascent project ( Kozminski et al. , 1993a ). As I learned, a quick end can be a good thing. The swan song of my tubulin project, and the first step toward the discovery of IFT, was the December 1991 American Society for Cell Biology meeting in Boston. The night before the meeting, my dissertation advisor Joel Rosenbaum aptly deemed the micrographs on my poster substandard. What ensued, learning that it is never too early to start a poster, was an all-nighter with my coauthor Dennis Diener, reprinting micrographs from photo negatives. With the sun rising, I had just enough time to catch an early morning train to Boston. As the Amtrak train swayed out of New Haven station I heard the voice barking, “Kozminski, Wake up!” It was no dream. Rosenbaum was in the aisle, talking about tubulin acetylation and my need for dissertation plan B. In serious outside voice, he said, “You need to look at Bloodgood's Balls.” I concurred. Heads turned. There was certainly no better conversation on which to eavesdrop that morning. Chlamydomonas flagella are an outstanding model for substrate–cell surface interactions. This became clear in 1977, when Robert Bloodgood, then a postdoc in the Rosenbaum lab, discovered a novel flagellar motility that is independent of flagellar beating. He found that polystyrene balls attached to the surface of a flagellum move in a rapid, bidirectional, saltatory manner ( Bloodgood, 1977 ). This ball movement is thought to be a manifestation of whole-cell gliding motility, which occurs when Chlamydomonas cells move along a substrate via their flagella, in a manner completely independent of flagellar beating. To this day, the mechanism of whole-cell gliding is not fully known and remains a very ripe area for research in cell signaling at cell surface–substrate interfaces. My question that morning on Amtrak was, “What are we looking for?” Rosenbaum wanted me to find the mechanism driving ball movement on the flagellar surface by using a permeabilized cell model. He made the pitch, telling me about earlier studies on dynein reactivation. I countered, saying we should look for kinesins within the flagellum, because ball movement is bidirectional and dyneins, which seemed well studied at the time, may only be applicable to motility in one direction. I recall that my favoritism of kinesin over dynein was only because kinesin was a relatively new discovery and hence “cool.” Rosenbaum liked my kinesin idea and launched into a 60-mile explanation of how cilia/flagella are the same as neurons; that is, if kinesin was found in axoplasm, it will be found in a flagellum. Sixty miles on Amtrak is a long time. That was it—after the winter holidays, I was to search for the flagellar kinesins driving ball movement on the flagellar surface by using a permeabilized cell model. The new year brought a new discussion. On returning from the holidays, Rosenbaum and Mark Mooseker, also on my dissertation committee, pushed me hard to work on radial spoke assembly. Spokes are the protein complexes that extend from the central pair of microtubules of the axoneme toward the outer doublet microtubules. In Petrine style, I refused three times. I said, “Spokes are boring ,” relative to molecular motors. In the end, I prevailed, and Rosenbaum permitted me to explore, at least for a short time, flagellar surface motility, as we had discussed on the train to Boston. I was extremely fortunate to have an advisor who allowed explorative forays. It made science extra fun. And, so the record is clear, Rosenbaum was not wrong in his push for radial spoke research. Spok
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