Phosphorylation of ezrin on threonine T567 plays a crucial role during compaction in the mouse early embryo

Abstract

The preimplantation development of the mouse embryo leads to the divergence of the first two cell lineages, the inner cell mass and the trophectoderm. The formation of a microvillus pole during compaction at the eight-cell stage and its asymmetric inheritance during mitosis are key events in the emergence of these two cell populations. Ezrin, a member of the ERM protein family, seems to be involved in the formation and stabilization of this apical microvillus pole. To further characterize its function in early development, we mutated the key residue T567, which was reported to be essential for regulation of ezrin function through phosphorylation. Here, we show that expression of ezrin mutants in which the COOH-terminal threonine T567 was replaced by an aspartate (to mimic a phosphorylated residue; T567D) or by an alanine (to avoid phosphorylation; T567A) interferes with E-cadherin function and disrupts the first morphogenetic events of development: compaction and cavitation. The active mutant ezrin-T567D induces the formation of numerous and abnormally long microvilli at the surface of blastomeres. Moreover, it localizes all around the cell cortex and inhibits cell-cell adhesion and cell polarization at the eight-cell stage. During the following stages, only half of the embryos are able to compact and finally to cavitate. In those embryos, the amount of ezrin-T567D decreases in the basolateral areas, while the proportion of adherens junctions increases. The reverse inactive mutant ezrin-T567A is mainly cytoplasmic and does not perturb compaction at the eight-cell stage. However, at the 16-cell stage, it relocalizes at the basolateral cortex, leading to a strong decrease in the surface of adherens junctions, and finally, embryos abort development. Our results show that ezrin is directly involved in the formation of microvilli in the early mouse embryo. Moreover, they indicate that maintenance of ezrin in basolateral areas prevents microvilli breakdown and inhibits the formation of normal cell-cell contacts mediated by E-cadherin, thereby impairing blastomeres polarization and morphogenesis of the blastocyst.

The actin-cytoskeleton linker protein ezrin is regulated during osteosarcoma metastasis by PKC

“…This linker function makes ezrin essential for many fundamental cellular processes, including the determination of cell shape, polarity and surface structure, cell adhesion, motility, cytokinesis, phagocytosis and integration of membrane transport with signaling pathways (Serrador et al, 1999;Ng et al, 2001;Bretscher et al, 2002;Wu et al, 2004). Ezrin is expressed in many normal tissues and has been demonstrated to be important during embryogenesis (Dard et al, 2004;Polesello and Payre, 2004;Saotome et al, 2004). Nonetheless, the redundancy that exists between ezrin and the other ERM proteins may be sufficient to compensate for the loss of ezrin in some physiological processes.…”

Phosphorylated ezrin is located in the nucleus of the osteosarcoma cell

“…11,12 Phosphorylation of ezrin promotes morphogenesis of apical microvilli and regulates E-cadherindependent adherent junction assembly. [13][14][15] Ezrin directly interacts with signaling enzymes such as phosphoinositide 3-kinase (PI3-kinase), and the phosphorylated tyrosine 353 (Tyr-353) residue of ezrin is regulated through the PI3-kinase/Akt pathway. 11 Ezrin is also preferentially degraded and resynthesized after oxidative stress 16 and the phosphorylation at threonine 567 (Thr-567) depends on the p38 MAP-kinase activity.…”

Morphogenesis of the mammalian blastocyst

“…The cytoskeleton protein ezrin is another good candidate (Louvet-Vallée et al, 2001). We have shown that phosphorylation of ezrin on T567 regulates its localization at the time of compaction and that maintenance of ezrin at the basolateral cortex at the 8-cell stage, interferes with the activity of E-cadherin and inhibits the formation of normal cell-cell contacts (Dard et al, 2004).…”

“…The removal of microvilli at the basolateral membrane, is crucial to allow flattening (Dard et al, 2004). Ezrin, a cytoskeleton protein linking actin to the plasma membrane in diverse types of membrane protrusions, follows exactly the distribution of microvilli: before compaction it is distributed all around the cell cortex and during polarization, it is removed from cell-cell contacts and relocates exclusively at the apical pole of blastomeres (Louvet et al, 1996).…”