title: Topological control of life and death in non-proliferative epithelia.
abstract: Programmed cell death is one of the most fascinating demonstrations of the plasticity of biological systems. It is classically described to act upstream of and govern major developmental patterning processes (e.g. inter-digitations in vertebrates, ommatidia in Drosophila). We show here the first evidence that massive apoptosis can also be controlled and coordinated by a pre-established pattern of a specific 'master cell' population. This new concept is supported by the development and validation of an original model of cell patterning. Ciona intestinalis eggs are surrounded by a three-layered follicular organization composed of 60 elongated floating extensions made of as many outer and inner cells, and indirectly spread through an extracellular matrix over 1200 test cells. Experimental and selective ablation of outer and inner cells results in the abrogation of apoptosis in respective remaining neighbouring test cells. In addition incubation of outer/inner follicular cell-depleted eggs with a soluble extract of apoptotic outer/inner cells partially restores apoptosis to apoptotic-defective test cells. The 60 inner follicular cells were thus identified as 'apoptotic master' cells which collectively are induction sites for programmed cell death of the underlying test cells. The position of apoptotic master cells is controlled by topological constraints exhibiting a tetrahedral symmetry, and each cell spreads over and can control the destiny of 20 smaller test cells, which leads to optimized apoptosis signalling.
authors.affiliation: Université Montpellier 2, UMR CNRS 5554, Institut des Sciences de l'Evolution, Montpellier, France.
authors.forename: Camille
authors.initials: C
authors.lastname: Martinand-Mari
authors.forename: Benoit
authors.initials: B
authors.lastname: Maury
authors.forename: François
authors.initials: F
authors.lastname: Rousset
authors.forename: Alain
authors.initials: A
authors.lastname: Sahuquet
authors.forename: Gérard
authors.initials: G
authors.lastname: Mennessier
authors.forename: Sergei
authors.initials: S
authors.lastname: Rochal
authors.forename: Vladimir
authors.initials: V
authors.lastname: Lorman
authors.forename: Paul
authors.initials: P
authors.lastname: Mangeat
authors.forename: Stephen
authors.initials: S
authors.lastname: Baghdiguian
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002938:Ciona intestinalis; D004847:Epithelial Cells / Q000166:cytology*; D005260:Female; D006080:Ovarian Follicle / Q000166:cytology; D010063:Ovum / Q000166:cytology