The Actomyosin Cytoskeleton of Amoebae of the Cellular Slime MoldsAcrasis roseaandProtostelium mycophaga: Structure, Biochemical Properties, and Function

Hellstén, Maarit; Roos, Urs-Peter

doi:10.1006/fgbi.1998.1048

Cited by 6 publications

(2 citation statements)

References 88 publications

(124 reference statements)

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“…While our data confirm previous descriptions of Naegleria contractile vacuole dynamics, 1, 47, 60 they refute previous hypotheses of how contractile vacuoles pump. Despite the popularity of the actomyosin contractility hypothesis in the literature, 10, 13, 32, 34–36, 84 we and others failed to observe actin around active contractile vacuole bladders in any species, 16, 85–88 and disassembly of all actin networks in Naegleria and Dictyostelium failed to halt water expulsion. Furthermore, analytical modeling of this mechanism is unable to explain the dynamics of contractile vacuole emptying in Paramecium.…”

Section: Discussioncontrasting

confidence: 70%

A conserved pressure-driven mechanism for regulating cytosolic osmolarity

Garner

Beckford

Weeda

et al. 2023

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Controlling intracellular osmolarity is essential to all cellular life. Cells that live in hypo-osmotic environments like freshwater must constantly battle water influx to avoid swelling until they burst. Many eukaryotic cells use contractile vacuoles to collect excess water from the cytosol and pump it out of the cell. Although contractile vacuoles are essential to many species, including important pathogens, the mechanisms that control their dynamics remain unclear. To identify basic principles governing contractile vacuole function, we here investigate the molecular mechanisms of two species with distinct vacuolar morphologies from different eukaryotic lineages—the discobanNaegleria gruberi, and the amoebozoan slime moldDictyostelium discoideum. Using quantitative cell biology we find that, although these species respond differently to osmotic challenges, they both use actin for osmoregulation, as well as vacuolar-type proton pumps for filling contractile vacuoles. We also use analytical modeling to show that cytoplasmic pressure is sufficient to drive water out of contractile vacuoles in these species, similar to findings from the alveolateParamecium multimicronucleatum. Because these three lineages diverged well over a billion years ago, we propose that this represents an ancient eukaryotic mechanism of osmoregulation.

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Section: Discussioncontrasting

confidence: 70%

A conserved pressure-driven mechanism for regulating cytosolic osmolarity

Garner

Beckford

Weeda

et al. 2023

Preprint

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“…The acrasid life cycle is strikingly similar to that of dictyostelids (Baldauf & Strassmann 2017), and acrasids were long considered their primitive relatives (van Tieghem 1880). Due at least in part to this presumed close relationship Acrasis rosea (now Acrasis kona) enjoyed some popularity as an experimental model, especially for the study of cytoskeletal and related features (e.g., Hellstén and Roos 1998). However, the amoebae of acrasids and dictyostelids differ markedly in both morphology and behavior (Olive 1975, Page andBlanton 1985), and molecular phylogeny now places them widely separated in the eukaryote tree.…”

Section: Introductionmentioning

confidence: 99%

Deep origins of eukaryotic multicellularity revealed by the Acrasis kona genome and developmental transcriptomes

Sheikh

Brown

et al. 2023

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Acrasids are large, fast-moving, omnivorous amoebae. However, under certain conditions, they can also cooperate to form multicellular fruiting bodies in a process known as aggregative multicellularity (AGM). This makes acrasids the only known example of multicellularity among the earliest branches of eukaryotes (formerly superkingdom Excavata) and thus the outgroup to all other known multicellular eukaryotes. We have sequenced the genome of Acrasis kona, along with transcriptomes from cells in pre-, mid- and post-development. We find the A. kona genome to be rich in novelty, genes acquired by horizontal transfer and, especially, multigene families. The latter include nearly half of the amoeba’s protein coding capacity, and many of these families show differential expression among life cycle stages. Development in A. kona appears to be molecularly simple, requiring substantial upregulation of only 449 genes compared to 2762 in the only other AGM model, Dictyostelium discoideum. However, unlike the dictyostelid, developing A. kona also does not appear to be starving, being instead very metabolically active and inducing neither autophagy nor increasing ubiquitin-tagged proteolysis. Thus, contrary to current expectations, starvation does not appear to be essential for AGM development. Moreover, despite the ~ 2 billion years of evolution separating the two amoebae, their development appears to employ remarkably similar pathways for signaling, motility and construction of an extracellular matrix surrounding the developing cell mass. In addition, much of this similarity is shared with the clonal multicellularity of animals. This makes the acrasid something of a “bare bones” developmental model and suggests that much of the basic tool kit for multicellular development arose very early in eukaryotic evolution.

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