Flagella and cilia are structurally polarized organelles whose lengths are precisely defined, and alterations in length are related to several human disorders [1, 2]. Intraflagellar transport (IFT) and protein signaling molecules are implicated in specifying flagellar and ciliary length [3-6], but evidence has been lacking for a flagellum and cilium length sensor that could participate in active length control or establishment of structural polarity. Previously, we showed that the phosphorylation state of the aurora-like protein kinase CALK in Chlamydomonas is a marker of the absence of flagella. Here we show that CALK phosphorylation state is also a marker for flagellar length. CALK is phosphorylated in cells without flagella, and during flagellar assembly it becomes dephosphorylated. Dephosphorylation is not simply a consequence of initiation of flagellar assembly or of time after experimentally induced flagellar loss, but instead requires flagella to be assembled to a threshold length. Analysis of cells with flagella of varying lengths shows that the threshold length for CALK dephosphorylation is ∼6 μm (half length). Studies with short and long flagellar mutants indicate that cells detect absolute rather than relative flagellar length. Our results demonstrate that cells possess a mechanism for translating flagellar length into a posttranslational modification of a known flagellar regulatory protein.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Agricultural and Biological Sciences(all)