Rho-regulated Myosin phosphatase establishes the level of protrusive activity required for cell movements during zebrafish gastrulation

Abstract

Rho-dependent amoeboid cell movement is a crucial mechanism in both tumor cell invasion and morphogenetic cell movements during fish gastrulation. Amoeboid movement is characterized by relatively non-polarized cells displaying a high level of bleb-like protrusions. During gastrulation, zebrafish mesodermal cells undergo a series of conversions from amoeboid cell behaviors to more mesenchymal and finally highly polarized and intercalative cell behaviors. We demonstrate that Myosin phosphatase, a complex of Protein phosphatase 1 and the scaffolding protein Mypt1, functions to maintain the precise balance between amoeboid and mesenchymal cell behaviors required for cells to undergo convergence and extension. Importantly, Mypt1 has different cellautonomous and non-cell-autonomous roles. Loss of Mypt1 throughout the embryo causes severe convergence defects, demonstrating that Mypt1 is required for the cell-cell interactions involved in dorsal convergence. By contrast, mesodermal Mypt1 morphant cells transplanted into wild-type hosts undergo dorsally directed cell migration, but they fail to shut down their protrusive behavior and undergo the normal intercalation required for extension. We further show that Mypt1 activity is regulated in embryos by Rho-mediated inhibitory phosphorylation, which is promoted by non-canonical Wnt signaling. We propose that Myosin phosphatase is a crucial and tightly controlled regulator of cell behaviors during gastrulation and that understanding its role in early development also provides insight into the mechanism of cancer cell invasion.

Epithelial relaxation mediated by the myosin phosphatase regulator Mypt1 is required for brain ventricle lumen expansion and hindbrain morphogenesis

“…Another possibility is that wild-type cells must be fully connected through junctions in the epithelial sheet in order to undergo correct shape change. Interestingly, a similar duality of cell-autonomous and non-autonomous phenotype has also been observed for mypt1 function during convergent extension (Weiser et al, 2009).…”

“…Myosin II is required for proper sheet movement and cell shape during Drosophila dorsal closure (Mizuno et al, 2002;Tan et al, 2003). In zebrafish, Mypt1 is important for kidney formation and for convergent extension during gastrulation (Huang et al, 2008;Weiser et al, 2009).…”

The guanine nucleotide exchange factor Net1 facilitates the specification of dorsal cell fates in zebrafish embryos by promoting maternal β-catenin activation

“…Net1 specifically interacts with both GTP-and GDP-bound RhoA and catalyzes GDP exchange on RhoA, but not Rac1 or Cdc42 [34,68]. Moreover, our results, as well as those from previous genetic studies, indicate that RhoA mediates cell movements during zebrafish gastrulation but not cell fate determination [41,92,93]. Conversely, intracellular GTP-Rac1 and GTP-cdc42, but not activated RhoA, are known to disrupt PAK1 dimerization, thereby controlling β-catenin S675 phosphorylation and Wnt signal transduction [23,65].…”

ApoA-II Directs Morphogenetic Movements of Zebrafish Embryo by Preventing Chromosome Fusion during Nuclear Division in Yolk Syncytial Layer

“…Cell Migration Analysis by UV-mediated PhotoactivationEmbryos were injected and imaged at bud stage for analysis of convergence and extension as described (30).…”