Myosin rings and spreading in mouse blastomeres.

Abstract

The relationship between myosin organization and cell spreading in the preimplantation mouse embryo was studied by indirect immunofluorescence in embryos cultured on lectin-coated substrates. Binding of cell surface polysaccharides to substrate-bound concanavalin A and wheat germ agglutinin induced changes in myosin distribution that resembled those which occur during cell-cell contact interaction. This involved an initial loss of myosin from the contact region that was associated with the development of stable cell-substrate attachments. In addition, a ring of myosin was formed along the edge of the cells' contact to the substrate. The presence of such a ring may be related to the potential for subsequent cell spreading. A myosin ring was also identified in the apical junctional region of the outer morula cells where it similarly separated the cell periphery into contacted and free peripheral domains. Following these changes in myosin organization the embryos spread on the substrate by extension of lamellipodia. These movements were coupled to the dissolution of the myosin ring and the reorganization of myosin into filament bundles. The sequence of changes in the pattern of myosin distribution suggests that contact regulation of myosin organization plays an important role in controlling the spreading behavior of blastomeres and perhaps more generally in the organization of cells into epithelia.A major morphological change takes place in the eight-cell mouse embryo when the rounded blastomeres spread and flatten against each other. This process of compaction has an important influence on blastocyst formation and differentiation of the epithelial trophoblast. It involves active cell movement (15) and appears to be related to changes in adhesiveness (14,15,25) and to cytoskeletal reorganization (6, 7).The cortex of compacting blastomeres contains a network of microfilaments (7) and immunofluorescent localization shows a continuous layer of cortical actin (16). Myosin, on the other hand, exhibits a polarized cortical distribution (22). It forms a continuous cortical layer in the uncontacted apical region of the cells and is not detectable in regions of cell contact. The loss of myosin from the contact regions is mediated by contacted interaction between the blastomeres and may play a role in the development of stable cellular associations (23). Contact modulated loss of myosin begins in the two-cell embryo and continues through the morula stages (23). It is therefore unlikely to serve as the only indication of myosin involvement during compaction. If myosin has a specific role in compaction one might expect to see a new pattern of myosin organization in which one element would be the missing patch of cortical myosin.The present study was designed to see if spreading is associated with such a specific pattern of myosin organization. Blastomeres spread on lectin coated substrates (14) and this system was adapted to examine the temporal relationship between myosin organization and spreading. The results show ...

Changes in the distribution of vinculin during preimplantation mouse development

“…Comparable ring-like concentrations of spectrin have also been found in embryos, but, interestingly, their localization in contact areas is slightly more peripheral than that of the corresponding rings of actin [41]. Myosin has also been found to concentrate in a comparable fashion in the apical junctional region of outer morula cells [45].…”

Extracellular matrix-dependent myosin dynamics during G1-S phase cell cycle progression in hepatocytes

“…Many previous reports have shown a role for myosin in cell shape changes [19,[37][38][39]. Hence, the role myosin plays in hepatocyte spreading was examined by disrupting myosin activity using two pharmacological inhibitors of myosin, BDM and ML-9, and the actin polymerizationinhibiting drug cytochalasin D. BDM is a myosin inhibitor that is believed to bind the actomyosin complex and freeze it in the phosphate-bound form [40].…”

From Egg to Epithelium

“…During early cleavage, microfi laments in interphase cells are confined largely to microvilli and to a thin cytocortical mesh associated with alpha-actinin, alpha-spectrin, vinculin, and myosin. The mesh is distributed homogeneously except immediately subjacent to points of contact between cells, where dis assembly of micro filaments and loss of myosin and spectrin seems to occur ( Figure 3) (Ducibella et al 1977;Opas & Soltynska 1978;Lehtonen & Badley 1980;Sobel 1983Sobel , 1984 On reaching the 8-cell stage, the process of epithelialization commences, and a redistribution of microfilaments occurs ( Figure 3). Microvilli in the presumptive basolateral region of each blastomere shorten, while those in the apical region lengthen, which leads to the establishment of clearly defi ned structural domains.…”