Effect of inhibition of axonemal dynein ATPases on the regulation of flagellar and ciliary waveforms in Leishmania parasites

Abstract

Trypanosomes of the genus Leishmania swim by undulating motions of a single flagellum driven by axonemal dynein ATPases, essential for parasite survival and infectivity. The flagellum possesses two waveforms; flagellar (tip-to-base) responsible for forward movements and ciliary (base-to-tip) possibly responsible for reorientation in response to changes in surroundings. However, the role of dyneins in regulating the two waveforms remains unknown. Moreover, the unpredictable nature of the parasite ciliary waveform makes it difficult to study. We have previously reported a detergent-extracted, ATP-reactivated model ideal for investigating flagellar motility regulation in Leishmania that allows one to generate reactivated Leishmania flagella with constitutively beating ciliary waves in presence of cyclic-AMP. Here, using three dynein inhibitors [erythro-9-(2-hydroxy-3-nonyl) adenine, ciliobrevin A and vanadate] we investigated the role of dyneins in regulating the two waveforms of Leishmania. Using high speed videomicroscopy we observed differential inhibition of beat frequencies and waveforms of flagellar and ciliary beats in live (in vivo) and ATP-reactivated (in vitro) parasites. Beat frequency of flagellar waveform was more strongly reduced than ciliary waveform. Surprisingly, inhibition of the ciliary waveform led to an altered phenotype with the distal half of the flagellum paralysed. ATPase assays confirmed that dynein activity of flagellar cells was more strongly inhibited compared to ciliary cells irrespective of the mechanism of inhibition. Possibly the two different waveforms are an outcome of changes in the mechanical properties of axonemal dyneins present at the tip of the flagellum that contains a sliding resistive structure. Our study suggests that dyneins responsible for the two waveforms in Leishmania bear different structural and functional conformations. Moreover, during ciliary beating, there is heterogeneity along the flagellum.