The distribution of myosin II in Dictyostelium discoideum slug cells.

Abstract

Abstract. While the role of myosin II in muscle contraction has been well characterized, less is known about the role of myosin II in non-muscle cells. Recent molecular genetic experiments on Dictyostelium discoideum show that myosin II is necessary for cytokinesis and multicellular development. Here we use immunofluorescence microscopy with monoclonal and polyclonal antimyosin antibodies to visualize myosin II in cells of the multicellular D. discoideum slug.M YOSIN II is found in all myocytes and in most eukaryote cells (Kom and Hammer, 1988;Warrick and Spudich, 1987) where it is implicated in cytokinesis (Fujiwara and Pollard, 1976;De Lozanne and Spudich, 1987;Knecht and Loomis, 1987; KitanishiYumura and Fukui, 1989), the control of cell shape (Wessels et al ., 1988), the motility of cells (Yumura et al., 1984;Rubino et al., 1984;Spudich and Spudich, 1982 ;Honer, 1988), the maintenance of cell polarity (Fukui et al., 1990), and the capping of membrane receptor proteins (Pasternak et al ., 1989). In multicellular organisms, myosin II may also play an important role in cell-cell interactions . Studies suggest that actomyosin bands are responsible for folding sheets of epithelia during gastrulation (Odell et al., 1981;Lee et al., 1983) and that myosin II is involved in both mouse morula compaction (Sobel, 1983 ; and resistance to stress in the embryonic chick area opaca (MonnetTschudi and Kucera, 1988) . Other studies involving gene disruption indicate that myosin II is necessary for normal multicellular development in Diciyostelium discoideum (see below) .D. discoideum is a simple, mobile eukaryote that can exist as an amoeba or as a multicellular aggregate (Bonner, 1967;Raper, 1984). D. discoideum thus lends itself to the study of both single cells and three-dimensional tissues. The cytoskeletal proteins ofindividual amoebae have been widely studied (Spudich and Spudich, 1982;Rubino et al., 1984;Fukui et al., 1987;Condeelis et al., 1987;Knecht and Loomis, 1987;De Lozanne and Spudich, 1987;Gerisch et al., 1989), however, those in multicellular aggregates have not .Mutant D. discoideum cells that lack myosin II survive and undergo (albeit slow) amoeboid movement; such cells differentiate into the two types which normally constitute a slug (prestalk and prespore cells) and theyaggregate to form loose mounds ofcells (Knecht and Loomis, 1987 A subpopulation of peripheral and anterior cells label brightly with antimyosin II antibodies, and many of these cells display a polarized intracellular distribution of myosin II. Other cells in the slug label less brightly and their cytoplasm displays a more homogeneous distribution of myosin II. These results provide insight into cell motility within a three-dimensional tissue and they are discussed in relation to the possible roles of myosin II in multicellular development . Wessels et al ., 1988 ;Peters et al ., 1988;Manstein et al., 1989) . Atthis point, development is blocked : aggregates of myosin-deficient mutants fail to become mobile-they do not form slugs with norm...

Migration of Dictyostelium slugs: Anterior‐like cells may provide the motive force for the prespore zone

“…Therefore, the mechanisms by which inner cells can transfer forces to the substratum remain unclear. Dallon and Othmer predicted that only cells in contact with the substratum can reasonably gain traction to produce a motive force for the slug [Dallon and Othmer, 2004] in agreement with the interpretation of the myosin II distribution in slugs [Eliott et al, 1991].…”

“…However, this model predicts also a large vertical component proportional to the sine of the contact angle [Rieu et al, 2004[Rieu et al, , 2005. When examined from frozen section [Eliott et al, 1991], the contact angle of slugs on agar is around 1258. Rafols et al [2001a,b] measured a linear relation H $ 0.59 W between slug height H and width W for a broad range of sizes from lateral and side view pictures.…”

“…Assuming one spring per cell for clarity, only the last cell in contact with the substratum (i.e., cell C in the inset of Fig. 7a) is providing a net out- For a contact angle y 5 1258, i.e., the experimental value observed from frozen section [Eliott et al, 1991], a huge vertical deformation is predicted with this shell tension model. For a contact angle y 5 1558, the vertical deformation is within the experimental vertical resolution of the microscope (see Materials and Methods section).…”

Cell Movements and Mechanical Force Distribution During the Migration of Dictyostelium Slugs

“…Only prespore cells propel the slug forward due to their close contact to the substratum and the surrounding slime sheath [5]. On the other hand, earlier studies suggested that the more active anterior cells pull the posterior ones [7][8][9].…”

Role of B Regulatory Subunits of Protein Phosphatase Type 2A in Myosin II Assembly Control in Dictyostelium discoideum

“…Interestingly, both phr2aB␣ and phr2aB␤ gene disruption lines also displayed excessive slug formation, phenotypes that could be rescued with expression of FLAG-tagged phr2aB␣ constructs. Although myosin II is known to be expressed in slugs (6), its roles in slug migration are not well understood. We suggest that the slug phenotype, and possibly the developmental delay, may reflect functions of these B55 targeting subunits that are independent of myosin II.…”