The single flagellum ofLeishmaniahas a fixed polarisation of its asymmetric beat

Abstract

9Eukaryotic flagella undergo different beat types necessary for their function. The single flagellum on 10 Leishmania parasites, for example, undergoes a symmetric tip-to-base beat for forward swimming 11 and an asymmetric base-to-tip beat to rotate the cell. Asymmetric beats are most commonly 12 associated with multi-ciliated tissues or organisms where the asymmetry has a constant polarisation. 13We asked whether this also holds for the single Leishmania flagellum. To do so, we used high frame 14 rate dual colour fluorescence microscopy to visualise intracellular and intraflagellar structure in live 15 swimming cells. This showed that the asymmetric Leishmania beat has a fixed polarisation. As in 16Chlamydomonas, this asymmetry arose from an asymmetric static curvature combined with a 17 symmetric dynamic curvature. Some axoneme protein deletion mutants give flagella which retain 18 static curvature, but lack dynamic curvature. We saw that these retain a fixed polarisation. Similarly, 19 deletion mutants which disrupt vital asymmetric extra-axonemal and rootlet-like flagellum-20 associated structures also retain a fixed polarisation. This indicated that beat asymmetry does not 21 originate from rootlet-like and extra-axonemal structures and is likely intrinsic to either the nine-fold 22 rotational symmetry of the axoneme structure or due to differences between the outer doublet 23 decorations. 24 >90°) ( Figure 2F). The dynamic curvature of the flagellum can be determined by subtracting the static 129 curvature. This corresponds to the propagating wave shape on the underlying static shape of the 130 flagellum. The dynamic curvature of both the tip-to-base and base-to-tip beats are near-symmetric, 131 however the base-to-tip beats often do not propagate along the entire flagellum ( Figure 2F). For the 132