Actin dynamics in Amoeba proteus motility

Abstract

We studied the distribution of the endogenous Arp2/3 complex in Amoeba proteus and visualised the ratio of filamentous (F-actin) to total actin in living cells. The presented results show that in the highly motile Amoeba proteus, Arp2/3 complex-dependent actin polymerisation is involved in the formation of the branching network of the contractile layer, adhesive structures, and perinuclear cytoskeleton. The aggregation of the Arp2/3 complex in the cortical network, with the exception of the uroid and advancing fronts, and the spatial orientation of microfilaments at the leading edge suggest that actin polymerisation in this area is not sufficient to provide the driving force for membrane displacement. The examined proteins were enriched in the pinocytotic pseudopodia and the perinuclear cytoskeleton in pinocytotic amoebae. In migrating amoebae, the course of changes in F-actin concentration corresponded with the distribution of tension in the cell cortex. The maximum level of F-actin in migrating amoebae was observed in the middle-posterior region and in the front of retracting pseudopodia. Arp2/3 complex-dependent actin polymerisation did not seem to influence F-actin concentration. The strongly condensed state of the microfilament system could be attributed to strong isometric contraction of the cortical layer accompanied by its retraction from distal cell regions. Isotonic contraction was limited to the uroid.

A short history of blebbing

“…In amoeba proteus, an actin cortex is attached to the entirety of the membrane except at the growing pseudo‐podium. Growing pseudo‐podia alternate periods of rapid growth (7 μm s −1 ) during which the membrane is delaminated from the actin cortex owing to the apparition of a crack and periods of stalling when an actin cortex is reassembled (Pomorski et al , 2007). In amoeba motility, uroid contraction gives rise to hydrostatic pressure, which powers cytosolic streaming and motility (Grebecka & Grebecki, 1981; Yanai et al , 1996).…”

Rotation of stress fibers as a single wheel in migrating fish keratocytes

“…One is a combination of the expansion of the front by actin polymerization 7 – 10 and retraction of the rear by actomyosin contraction 11 shown in fibroblasts 12 – 14 , neutrophils 5 , 15 – 18 and Dictyostelium cells 5 , 19 , 20 . The other is bleb-driven migration such as extension of the front cortex by strong actomyosin contraction at the rear, shown in the migrating protist Amoeba proteus 21 , 22 .…”

Cytoskeletal architecture and its evolutionary significance in amoeboid eukaryotes and their mode of locomotion

“…Mechanism of amoeboid movement and morphodynamic studies in Amoebozoa is poorly documented. Most studies related to this topic are based on a few lineages of amoebae, namely Dictyostelium [ 45 ], Acanthamoeba [ 42 ] and A. proteus [ 29 ]. It is generally believed that amoeboid movement in amoebae especially those with lobose pseudopodia are primarily driven by an actomyosin cytoskeleton [ 40 ].…”

“…Cytoplasmic MT architecture in these amoebae appears microscopically as non-overlapping uniform dots giving it the appearance of upright MT fibres in cross-sectional viewing (figure 1h,i). The cytoskeleton of Amoeba proteus has been extensively studied using various techniques [27][28][29][30]39]. While the role and presence of F-actin in Amoeba proteus is well established [28,29], the presence and detection of cytoplasmic MTs has been controversial and inconclusive.…”

“…In Amoeba proteus, with a lobopodium type of pseudopodia, the microfilament system (actin and myosin) is the main driving force of amoeboid movement [26][27][28][29]. The system of MTs in Amoeba proteus is poorly developed and its role is not well understood [30,31].…”