Two types of Chlamydomonas flagellar mutants missing different components of inner-arm dynein.
Two types of Chlamydomonas reinhardtii flagellar mutants (idaA and idaB) lacking partial components of the inner-arm dynein were isolated by screening mutations that produce paralyzed phenotypes when present in a mutant missing outer-arm dynein. Of the currently identified three inner-arm subspecies I1, I2, and I3, each containing two heterologous heavy chains (Piperno, G., Z. Ramanis, E. F. Smith, and W. S. Sale. 1990. J. Cell Biol. 110:379-389), idaA and idaB lacked I1 and I2, respectively. The 13 idA isolates comprised three genetically different groups (ida1, ida2, ida3) and the two idaB isolates comprised a single group (ida4). In averaged cross-section electron micrographs, inner dynein arms in wild-type axonemes appeared to have two projections pointing to discrete directions. In ida1-3 and ida4 axonemes, on the other hand, either one of them was missing or greatly diminished. Both projections were weak in the double mutant ida1-3 x ida4. These observations suggest that the inner dynein arms in Chlamydomonas axonemes are aligned not in a single straight row, but in a staggered row or two discrete rows. Both ida1-3 and ida4 swam at reduced speed. Thus, the inner-arm subspecies missing in these mutants are not necessary for flagellar motility. However, the double mutants ida1-3 x ida4 were nonmotile, suggesting that axonemes with significant defects in inner arms cannot function. The inner-arm dynein should be important for the generation of axonemal beating.
Kamiya
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R
Department of Molecular Biology, School of Science, Nagoya University, Japan.
Kurimoto
E
E
Muto
E
E
D002465:Cell Movement; D002696:Chlamydomonas / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D004398:Dyneins / Q000235:genetics* / Q000302:isolation & purification; D004591:Electrophoresis, Polyacrylamide Gel; D005407:Flagella / Q000502:physiology / Q000648:ultrastructure*; D046911:Macromolecular Substances; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D008854:Microscopy, Electron; D016296:Mutagenesis; D010641:Phenotype; D011995:Recombination, Genetic
D046911:Macromolecular Substances; D008769:Methylnitronitrosoguanidine; D004398:Dyneins