Unicellular Eukaryotes as Models in Cell and Molecular Biology

Abstract

Unicellular eukaryotes have been appreciated as model systems for the analysis of crucial questions in cell and molecular biology. This includes Dictyostelium (chemotaxis, amoeboid movement, phagocytosis), Tetrahymena (telomere structure, telomerase function), Paramecium (variant surface antigens, exocytosis, phagocytosis cycle) or both ciliates (ciliary beat regulation, surface pattern formation), Chlamydomonas (flagellar biogenesis and beat), and yeast (S. cerevisiae) for innumerable aspects. Nowadays many problems may be tackled with "higher" eukaryotic/metazoan cells for which full genomic information as well as domain databases, etc., were available long before protozoa. Established molecular tools, commercial antibodies, and established pharmacology are additional advantages available for higher eukaryotic cells. Moreover, an increasing number of inherited genetic disturbances in humans have become elucidated and can serve as new models. Among lower eukaryotes, yeast will remain a standard model because of its peculiarities, including its reduced genome and availability in the haploid form. But do protists still have a future as models? This touches not only the basic understanding of biology but also practical aspects of research, such as fund raising. As we try to scrutinize, due to specific advantages some protozoa should and will remain favorable models for analyzing novel genes or specific aspects of cell structure and function. Outstanding examples are epigenetic phenomena-a field of rising interest.

Proteolysis mediated by cysteine cathepsins and legumain—recent advances and cell biological challenges

“…& Fourth, there are reports from protozoans such as the ciliate Tetrahymena in which there seems to be a direct transport from the early endosomes into immature dense core granules thus bypassing the classical, retrograde pathway described above (Briguglio et al 2013;Turkewitz 2004). The alternative pathways of ciliates (Simon and Plattner 2014) may be understood as a form of detour recycling which does not follow the classical route from the plasma membrane to early and recycling endosomes back to the plasma membrane. A pathway like the one just described in ciliates might open up a possibility for molecules to rejoin the compartments of the secretory pathway before being secreted again in a regulated fashion.…”

Calcium signalling in the ciliated protozoan model, Paramecium: Strict signal localisation by epigenetically controlled positioning of different Ca2+-channels

“…Possible epigenetic mechanisms mediating such strict confinement of signalling have been discussed somewhere else [20]. There are good reasons to speculate that Ca 2+ may even be part of the epigenetic signals leading to the formation of the regular cell surface pattern [27].…”

“…Epigenetic control, particularly of cell surface pattern formation, is a salient feature of ciliates. Currently particularly this feature makes this group an interesting model for cell biologists [19,20]. On this basis we now envisage two main aspects.…”

Principles of Intracellular Signaling in Ciliated Protozoa—A Brief Outline

“…Intracellular signaling by pheromones (gamones) in ciliates (Luporini et al 2014) is summarized separately in this volume. Epigenetic signaling is also covered separately in this volume by Nowacki; for surveys, also see Chalker et al (2013) and Simon and Plattner (2014). Most of the other signaling mechanisms described here seem to be evolutionarily old and maintained from protozoa on, particularly ciliates, up to top-ranking metazoans.…”