The DHC1b (DHC2) isoform of cytoplasmic dynein is required for flagellar assembly

Dyneins are microtubule-based molecular motors involved in many different t ypes of cell movement. Most dynein heavy chains (DHCs) clearly group into c ytoplasmic or axonemal isoforms. However, DHC1b has been enigmatic, To lear n more about this isoform, we isolated Chlamydomonas cDNA clones encoding a portion of DHC1b, and used these clones to identify a Chlamydomonas cell l ine with a deletion mutation in DHC1b. The mutant grows normally and appear s to have a normal Golgi apparatus, but has very short flagella. The deleti on also results in a massive redistribution of raft subunits from a peri-ba sal body pool (Cole, D.G., D.R. Diener, A.L. Himelblau, P.L. Beech, J.C. Fu ster, and J.L. Rosenbaum. 1998. J. Cell Biol. 141:993-1008) to the flagella . Rafts are particles that normally move up and down the flagella in a proc ess known as intraflagellar transport (IFT) (Kozminski, K.G., K.A. Johnson, P. Forscher, and J.L. Rosenbaum. 1993. Proc. Natl. Acad. Sci. USA. 90:5519 -5523), which is essential for assembly and maintenance of flagella, The re distribution of raft subunits apparently occurs due to a defect in the retr ograde component of IFT, suggesting that DHC1b is the motor for retrograde IFT. Consistent with this, Western blots indicate that DHC1b is present in the flagellum, predominantly in the detergent- and ATP-soluble fractions. T hese results indicate that DHC1b is a cytoplasmic dynein essential for flag ellar assembly, probably because it is the motor for retrograde IFT.