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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-182
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-182
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 May 2019

Submitted as: research article | 23 May 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Dynamics and organization of actin-labelled granules as a rapid transport mode of actin cytoskeleton components in Foraminifera

Jan Goleń1, Jarosław Tyszka1, Ulf Bickmeyer2, and Jelle Bijma2 Jan Goleń et al.
  • 1ING PAN – Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Cracow, Biogeosystem Modelling Group, Senacka 1, 31-002 Kraków, Poland
  • 2AWI – Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany

Abstract. Recent advances in fluorescent imaging facilitate actualistic studies on organisms used for palaeoceanographic reconstructions. Observations of cytoskeleton organization and dynamics in living foraminifera foster understanding of morphogenetic and biomineralization principles. This paper describes the organisation of a foraminiferal actin cytoskeleton using in vivo staining based on fluorescent SiR-actin. Surprisingly, the most distinctive feature in the organisation of actin in Foraminifera is the prevalence of actin-labelled granules (ALGs) within pseudopodial structures. Fluorescent signal obtained from granules dominate over dispersed signal from the actin meshwork. Actin-labelled granules are small (around 1 µm in diameter) actin-rich organelles demonstrating a wide range of motility behaviours from almost stationary oscillating around certain points to exhibiting rapid motion. These structures are present both in Globothalamea (Amphistegina, Ammonia) and Tubothalamea (Quinqueloculina). They are found to be active in all kinds of pseudopodial ectoplasmic structures, including granuloreticulopodia, globopodia, and lamellipodia, as well as within the endoplasm itself. Two hypotheses regarding their function are proposed: (1) They are involved in endocytosis and intracellular transport of different kinds of cargo; (2) They transport prefabricated and/or recycled actin fibres to the sites where they are needed. These hypothesis are not mutually exclusive. The first hypothesis is based on the presence of similar actin structures in fungi, fungi-like protists and some plant cells. The later hypothesis is based on the assumption that actin granules are analogous to tubulin paracrystals responsible for efficient transport of tubulin. Actin patches transported in that manner are most likely involved in maintaining shape, rapid reorganization, and elasticity of pseudopodial structures, as well as in adhesion to the substrate. Finally, our comparative studies suggest that a large proportion of actin-labelled granules probably represent fibrillar vesicles and elliptical fuzzy coated vesicles often identified in TEM images. Correlative fluorescent electron microscopic observations are proposed to verify this interpretation.

Jan Goleń et al.
Jan Goleń et al.
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