Abstract. This paper presents novel results of experiments focused on actin cytoskeleton organisation in pseudopodial structures of foraminifera. The main aim of this research was to test the hypotheses proposed to explain the previously reported granular pattern of F-actin labelling in several species of foraminifera with SiR-actin fluorescent probe. These hypotheses include the possibility that SiR-actin enhances the F-actin polymerisation or that it binds to other than F-actin compounds within foraminiferal cells, resulting in capturing the staining artefacts. The series of replicated experiments conducted on small miliolid Quinqueloculina sp. included double staining of F-actin with SiR-actin and phalloidin-based probes, complemented with observations of reticulopodia under the polarised light to identify the granules showing birefringence. All of performed experiments demonstrate highly congruent results expressed in SiR-actin and phalloidin co-labelling patterns, especially pronounced with the small granular objects (SiR-actin labelled granules or ALGs). Furthermore, the birefringence strongly tends to characterise primarily areas stained with both of the probes. These results rule out staining artefacts and support existence of actin cytoskeleton associated with micrometre-size motile granules. We discuss possible implications of this granular pattern that facilitates efficient formation and fast reorganization of extended granuloreticulopodia and other pseudopodial structures. If this is the case, they are one of the key evolutionary adaptations of these organisms that most likely predates the evolution of the foraminiferal tests that started in the early Palaeozoic.

中文翻译：

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有孔虫中F-肌动蛋白的荧光双标记：网纹足病中颗粒状F-肌动蛋白组织的评估

摘要。本文提出了针对有孔虫假足结构中肌动蛋白细胞骨架组织的实验的新结果。这项研究的主要目的是检验提出的假设，以解释先前报道的几种带有SiR-actin荧光探针的有孔虫物种中F-actin标记的粒状模式。这些假设包括SiR-肌动蛋白增强F-肌动蛋白聚合或与有孔虫细胞内的F-肌动蛋白化合物以外的其他分子结合从而捕获染色伪影的可能性。在小型丁香喹啉基环孢菌素上进行的一系列重复实验sp。包括用SiR-actin和基于鬼笔环肽的探针对F-actin进行两次染色，并补充了在偏振光下观察网状伪足以鉴定显示双折射的颗粒。所有进行的实验均证明了以SiR-肌动蛋白和鬼笔环肽共标记模式表达的高度一致的结果，特别是在小颗粒物体（SiR-肌动蛋白标记的颗粒或ALG）中尤为明显。此外，双折射强烈倾向于主要表征被两种探针染色的区域。这些结果排除了染色伪影，并支持与微米级运动颗粒相关的肌动蛋白细胞骨架的存在。我们讨论了这种粒状模式的可能含义，该粒状模式有助于有效地形成和快速重组扩展的粒细胞伪足和其他伪足结构。