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J. Cell Biol.,
Volume 141, Number 4, May 18, 1998 979-992
Department of Cell Biology, University of Massachusetts Medical Center (UMMC), Worcester Foundation Campus,
Shrewsbury, Massachusetts 01545
Several enzymes, including cytoplasmic and
flagellar outer arm dynein, share an Mr 8,000 light chain
termed LC8. The function of this chain is unknown, but
it is highly conserved between a wide variety of organisms. We have identified deletion alleles of the gene
(fla14) encoding this protein in Chlamydomonas reinhardtii. These mutants have short, immotile flagella
with deficiencies in radial spokes, in the inner and outer
arms, and in the beak-like projections in the B tubule of
the outer doublet microtubules. Most dramatically, the
space between the doublet microtubules and the flagellar membrane contains an unusually high number of rafts, the particles translocated by intraflagellar transport (IFT) (Kozminski, K.G., P.L. Beech, and J.L.
Rosenbaum. 1995. J. Cell Biol. 131:1517-1527). IFT is a
rapid bidirectional movement of rafts under the flagellar membrane along axonemal microtubules. Anterograde IFT is dependent on a kinesin whereas the motor
for retrograde IFT is unknown. Anterograde IFT is
normal in the LC8 mutants but retrograde IFT is absent; this undoubtedly accounts for the accumulation of
rafts in the flagellum. This is the first mutation shown to
specifically affect retrograde IFT; the fact that LC8 loss
affects retrograde IFT strongly suggests that cytoplasmic dynein is the motor that drives this process. Concomitant with the accumulation of rafts, LC8 mutants
accumulate proteins that are components of the 15-16S
IFT complexes (Cole, D.G., D.R. Deiner, A.L. Himelblau, P.L. Beech, J.C. Fuster, and J.L. Rosenbaum.
1998. J. Cell Biol. 141:993-1008), confirming that these
complexes are subunits of the rafts. Polystyrene microbeads are still translocated on the surface of the flagella
of LC8 mutants, indicating that the motor for flagellar
surface motility is different than the motor for retrograde IFT.
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