A novel Chlamydomonas inner-arm-dynein-deficient mutant, ida10, harbors a mutation in a conserved protein with a PIH domain
Ryosuke Yamamoto1,2, Masafumi Hirono1 and Ritsu Kamiya1
1) Dept. Biol. Sciences, Graduate School of Science, Univ. of Tokyo, Tokyo, Japan
2) Dept. Cell Biology, Emory Univ. Sch. Med, Atlanta, GA 30322, USA
An important step in the formation of motile cilia and flagella is cytoplasmic pre-assembly of axonemal dyneins (Fowkes and Mitchell, 1998), but the underlying mechanisms are poorly understood. We isolated and analyzed a novel Chlamydomonas mutant, ida10, lacking a subset of single-headed inner-arm dyneins, and found that it has a mutation in a cytoplasmic protein, MOT48, conserved among organisms having motile cilia and flagella. This protein has a PIH domain, a domain that was first identified in Saccharomyces cerevisiae and thought to be involved in the pre-rRNA processing. Recently, the PIH domain was also found in PF13/KTU, a primary-ciliary-dyskinesia protein that has been suggested to participate in the pre-assembly of axonemal dyneins as a co-factor of heat shock protein(s) (Omran et al., 2008). The mutant ida10 has greatly reduced amounts of single-headed inner arm dynein subspecies b, c and d, while retaining normal or only slightly reduced amounts of subspecies a, e, f and g. The amount of outer arm dynein is also slightly reduced. Together with the previous report on pf13, which lacks outer arm dynein and inner arm dynein subspecies c (Omran et al., 2008), our results suggest that both PIH family proteins function in the pre-assembly of multiple axonemal dyneins. Chlamydomonas appears to use these proteins for outer arm dynein and some inner arm dynein subspecies separately, although their functions are somewhat redundant. In addition, database search detected a third PIH family protein, TWI1, in the Chlamydomonas genome. TWI1 is a putative homologue of the zebrafish TWISTER protein, the defects of which have been shown to cause polycystic kidney and curved body, which can be caused by defects in motile cilia (Sun et al., 2004). Thus, TWI1 may also be involved in the pre-assembly of dyneins.
e-mail address of presenting author: pantera.yamamoto@gmail.com