Abstract
Paramecium has served as a model organism for the studies of many aspects of genetics and cell biology: non-Mendelian inheritance, genome duplication, genome rearrangements, and exocytosis, to name a few. However, the large number and patterning of cilia that cover its surface have inspired extraordinary ultrastructural work. Its swimming patterns inspired exquisite electrophysiological studies that led to a description of the bioelectric control of ciliary motion. A genetic dissection of swimming behavior moved the field toward the genes and gene products underlying ciliary function. With the advent of molecular technologies, it became clear that there was not only great conservation of ciliary structure but also of the genes coding for ciliary structure and function. It is this conservation and the legacy of past research that allow us to use Paramecium as a model for cilia and ciliary diseases called ciliopathies. However, there would be no compelling reason to study Paramecium as this model if there were no new insights into cilia and ciliopathies to be gained. In this review, we present studies that we believe will do this. For example, while the literature continues to state that immotile cilia are sensory and motile cilia are not, we will provide evidence that Paramecium cilia are clearly sensory. Other examples show that while a Paramecium protein is highly conserved it takes a different interacting partner or conducts a different ion than expected. Perhaps these exceptions will provoke new ideas about mammalian systems.
Highlights
Microscopists in the 1600s were captivated by Paramecium species swimming behavior when examining infusoria [1]
Our studies showed that these two proteins, Pkd2 and XntA, interact at the C-terminus of Pkd2 in both the cilia and the cell membrane, and that most likely, Pkd2 is the Mg2+ channel in Paramecium and the XntA protein has some type of a stabilization role for Pkd2, and most likely other proteins as well [56]
Research on Paramecium has contributed and continues to contribute important findings about cell motility and cilia as well as genomics and cell biology [146]. (We had to be selective about what we included in this review, and our apologies to those whose fine research we were not able to include.) These organisms present some practical advantages in the study of cilia, and, because of conservation of many proteins in the development and function of cilia, Paramecium research can explore very close gene homologs and homologous structures
Summary
Microscopists in the 1600s were captivated by Paramecium species swimming behavior when examining infusoria [1]. There are other critical players in the formation of motile and primary cilia, such as the Bardet-Biedl syndrome (BBS) proteins, which form a cargo adapter to bring membrane and signaling proteins to the apparatus that moves them to and into the cilia, the Intraflagellar Transport (IFT) complexes [24,25] Failure of this BBSome to function properly leads to a constellation of symptoms of retinal degeneration, cystic kidneys, short fingers and genitalia, and more. The use of mass spectrometry has been instrumental in the identification of potential interacting partners as well as examining the proteins present in the ciliary membrane This approach can be used to examine changes in the ciliary proteins when certain gene products are depleted using RNAi. Numerous forms of microscopy can be used to study Paramecium and their cilia: Fluorescence. Stimulated Emission Depletion (STED) Microscopy can provide very detailed information on the spatial location of expressed proteins with epitope tags
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