Dynein-2 is the motor responsible for retrograde intraflagellar transport. In situ, dynein-2 comprises four subunits: the dynein-2 heavy chain (DYH2); the dynein-2 intermediate chain; the dynein-2 light-intermediate chain (D2LIC); and dynein light chain 8 (Rompolas et al. 2007. Chlamydomonas FAP133 is a dynein intermediate chain associated with the retrograde intraflagellar transport motor. J Cell Sci 120:3653-3665). In contrast to what has been reported in other model organisms, when the DYH2 gene or the D2LIC gene was disrupted in Tetrahymena, the cells continued to produce motile cilia that were not swollen or filled with material [Rajagopalan et al.2009. Dynein-2 affects the regulation of ciliary length but is not required for ciliogenesis in Tetrahymena thermophila. Mol Biol Cell 20:708-720]. When compared to wildtype cells, the dynein-2 mutants were found to have cilia that were at a lower density, shorter, and much more variable in length. One possible explanation for these effects is that the dynein-2 knockout cells grow cilia too slowly to enable them to achieve normal length and density before the cell divides. In the present study, dynein-2 knockout cells were deciliated and then allowed to regrow their cilia for 22 hr under conditions in which the cells did not divide. When dynein-2 was disabled, three effects were observed: (1) a decreased rate of cilia growth; (2) a lower cilia density that did not change over time; and (3) a wide distribution of cilia lengths that increased over time. These results confirm the importance of dynein-2 in regulating ciliary length in Tetrahymena. Cell Motil. Cytoskeleton, 2009. (c) 2009 Wiley-Liss, Inc.