title: Effect of head activator on proliferation, head-specific determination and differentiation of epithelial cells in hydra.
abstract: In hydra the differentiation of head-specific ectodermal epithelial cells from multipotent stem cells is a multistep process in which cell cycle progression is regulated at three restriction points. Head activator acts as a positive signal at these restriction points. At the G2/mitosis boundary of epithelial stem cells head activator functions as a mitogen, being necessary for cell division. Subsequently, in or before S phase, head activator acts as determinant to ensure commitment of epithelial cells to head-specific determination. This effect of head activator requires hundredfold-higher concentrations, and may also require longer incubation times, than for cell proliferation. Epithelial cells thus committed to head-specific differentiation become arrested in G2 as a third and last restriction point in the cell cycle. They require disinhibition by decapitation and probably the presence of head activator for final differentiation, which then occurs in G2.
authors.affiliation: Zentrum für Molekulare Biologie, Heidelberg, Federal Republic of Germany.
authors.forename: H C
authors.initials: HC
authors.lastname: Schaller
authors.forename: M
authors.initials: M
authors.lastname: Hofmann
authors.forename: L C
authors.initials: LC
authors.lastname: Javois
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004475:Ectoderm / Q000166:cytology* / Q000502:physiology; D004847:Epithelial Cells; D004848:Epithelium / Q000502:physiology; D006829:Hydra / Q000166:cytology*; D009024:Morphogenesis / Q000187:drug effects / Q000502:physiology; D009479:Neuropeptides / Q000494:pharmacology*; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D013270:Stomach / Q000166:cytology / Q000196:embryology / Q000502:physiology
chemical_list: D009479:Neuropeptides; C032522:head activator peptide; D011761:Pyrrolidonecarboxylic Acid