Abstract
Background Trypanosoma cruzi, the agent of Chagas disease, is a protozoan member of the Kinetoplastidae family characterized for the presence of specific and unique structures that are involved in different cell activities. One of them is the paraflagellar rod (PFR), a complex array of filaments connected to the flagellar axoneme. Although the function played by the PFR is not well established, it has been shown that silencing of the synthesis of its major proteins by either knockout of RNAi impairs and/or modifies the flagellar motility.Methodology/Principal FindingsHere, we present results obtained by atomic force microscopy (AFM) and transmission electron microscopy (TEM) of replicas of quick-frozen, freeze-fractured, deep-etched and rotary-replicated cells to obtain detailed information of the PFR structures in regions of the flagellum in straight and in bent state. The images obtained show that the PFR is not a fixed and static structure. The pattern of organization of the PFR filament network differs between regions of the flagellum in a straight state and those in a bent state. Measurements of the distances between the PFR filaments and the filaments that connect the PFR to the axoneme as well as of the angles between the intercrossed filaments supported this idea.Conclusions/SignificanceGraphic computation based on the information obtained allowed the proposal of an animated model for the PFR structure during flagellar beating and provided a new way of observing PFR filaments during flagellar beating.
Highlights
Much has been learned in the last decade on the structural organization of cells, mainly due to the development of and improvement in molecular, biochemical and microscopy methods
transmission electron microscopy (TEM) of thin sections at the areas indicated in Fig. 1a shows the emergence of the flagellum from the flagellar pocket and its initial association with the cell body
The paraflagellar rod (PFR) found in some protists is an excellent example of assembly of proteins into filamentous structures that interact with other filaments to form more complex assemblies
Summary
Much has been learned in the last decade on the structural organization of cells, mainly due to the development of and improvement in molecular, biochemical and microscopy methods. In the case of protozoa of the Trypanosomatidae family, which comprise important agents of human and animal diseases, the organization of cells has been previously analyzed in some detail using a combination of transmission electron microscopy (TEM) methods, such as observation of thin sections as well as replicas obtained after freeze-fracture [1]. A typical flagellum is formed by an axoneme composed of a 9+2 system of microtubule doublets enclosed by the flagellar membrane. Protein complexes forming the intraflagellar particles can be seen between the peripheral microtubule doublets and the flagellar membrane [3]. One of them is the paraflagellar rod (PFR), a complex array of filaments connected to the flagellar axoneme. The function played by the PFR is not well established, it has been shown that silencing of the synthesis of its major proteins by either knockout of RNAi impairs and/or modifies the flagellar motility
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