Abstract
Author SummaryDuring development, processes such as cell division, fate determination, migration, and removal of dead cells occur in a directional (i.e., polar) manner. For example, cell divisions in the early embryo often occur in a directional manner to maintain specific cell–cell interactions. Later, during organ formation, tissues may be shaped through polar cell migration. During apoptosis, a neighbouring cell engulfing a cell corpse utilizes polar positional information to deform its cytoskeleton and migrate around the corpse. Wnt pathway signalling is a common mechanism by which cells establish polarity during development, but how a single Wnt signal is translated into different outcomes in different cellular or developmental contexts is not clear. Our data on C. elegans suggest that during diverse directional events—cell engulfment, mitotic spindle movement, and cell migration—different Wnt ligands or a specific signal from a cell corpse signals to the Wnt receptor Frizzled (MOM-5 in C. elegans) and on to the downstream factors CED-10/Rac. But specificity of the Wnt signal is mediated by the use of distinct intermediate signal transduction pathways. Our discovery that this pathway is also used for engulfment of cell corpses led us to propose that the two parallel pathways, originally described for engulfment of corpses, are indeed parts of one pathway involving Wnt pathway components.
Highlights
Polar cellular processes are essential during development and maintenance of animals
The receptor initiating the engulfment of cell corpses in C. elegans remained, despite considerable efforts to define all components required for apoptosis genetically [5], elusive for many years
These results suggest that MOM-5/Fz function is required for efficient cell corpse clearance in C. elegans embryos
Summary
Polar cellular processes are essential during development and maintenance of animals. Cell cleavages and possibly associated cell-fate decisions have to be coordinated. But not least, supernumerary or sick cells must be removed by apoptosis, which requires a polar reorganisation of the cytoskeleton in the engulfing cell. Wnt signalling pathways have extremely diverse functions during these processes, including induction of cell fates or tumours, guidance of cell movements during gastrulation, and the induction of cell polarity [1,2]. Wnt can induce polar changes in cellular morphology by a remodelling of the cytoskeleton [3,4]. How activation of the Fz receptor induces cytoskeleton rearrangement is not well understood. The receptor initiating the engulfment of cell corpses in C. elegans remained, despite considerable efforts to define all components required for apoptosis genetically [5], elusive for many years
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