Identification of dyneins that localize exclusively to the proximal portion of Chlamydomonas flagella

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 2 µm region of the 12 µm 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.