Abstract
The movements of cilia and flagella are driven by multiple species of dynein heavy chains (DHCs), which constitute inner- and outer-dynein arms. In Chlamydomonas, 11 DHC proteins have been identified in the axoneme, but 14 genes encoding axonemal DHCs are present in the genome. Here, we assigned each previously unassigned DHC gene to a particular DHC protein and found that DHC3, DHC4 and DHC11 encode novel, relatively low abundance DHCs. Immunofluorescence microcopy revealed that DHC11 is localized exclusively to the proximal approximately 2 microm region of the approximately 12 microm long flagellum. Analyses of growing flagella suggested that DHC3 and DHC4 are also localized to the proximal region. By contrast, the DHC of a previously identified inner-arm dynein, dynein b, displayed an inverse distribution pattern. Thus, the proximal portion of the flagellar axoneme apparently differs in dynein composition from the remaining portion; this difference might be relevant to the special function performed by the flagellar base.
Highlights
Cilia and flagella are cell organelles that produce fluid flow over the surface of cells or propel cells in liquid media
We found by immunofluorescence microscopy that DHC11 preferentially localizes to the proximal ~2 μm portion of the axoneme
Mass-spectroscopic analysis of inner-arm dynein heavy chains (DHCs) The seven inner-arm dynein species previously identified in Chlamydomonas are made up of a total of eight DHCs (Kagami and Kamiya, 1992), of which only three have been correlated with particular DHC genes
Summary
Cilia and flagella are cell organelles that produce fluid flow over the surface of cells or propel cells in liquid media. Ciliary and flagellar movements are important in respiratory and reproductive processes, and recent studies have revealed their involvement in extracellular signal transduction related to various key steps in development. Cilia in the mammalian embryo convey signals that determine the left-right asymmetry of the body (Afzelius, 1985; Nonaka et al, 1998; Hirokawa et al, 2006). The movement of cilia and flagella is driven by multiple dynein molecules that constitute the inner and outer dynein arms of axonemes. Dyneins generate sliding force between adjacent outer doublets, which is converted to axonemal bending. The mechanism that converts the sliding movement into cyclical axonemal bending is not known, but most probably involves coordinated activities of dynein molecules with diverse properties
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