Morphogens and cell survival during development.
The notion of "morphogens" is an important one in developmental biology. By definition, a morphogen is a molecule that emanates from a specific set of cells that is present in a concentration gradient and that specifies the fate of each cell along this gradient. The strongest candidate morphogens are members of the transforming growth factor-beta (TGF-beta), Hedgehog (Hh), and Wnt families. While these morphogens have been extensively described as differentiation inducers, some reports also suggest their possible involvement in cell death and cell survival. It is frequently speculated that the cell death induction that is found associated with experimental removal of morphogens is the manifestation of abnormal differentiation signals. However, several recent reports have raised controversy about this death by default, suggesting that cell death regulation is an active process for shaping tissues and organs. In this review, we will present morphogens, with a specific emphasis on Sonic Hedgehog, a mammalian member of the Hh family, not as a positive regulators of cell differentiation but as key regulators of cell survival.
Mehlen
Patrick
P
Laboratoire Apoptose, Cancer et Développement, Equipe labelisée La Ligue, CNRS FRE2870, Centre Léon Bérard, 69008 Lyon, France. mehlen@lyon.fnclcc.fr
Mille
Fréderic
F
Thibert
Chantal
C
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D016923:Cell Death / Q000502:physiology; D002470:Cell Survival / Q000502:physiology*; D004330:Drosophila; D029721:Drosophila Proteins / Q000502:physiology; D053823:Hedgehog Proteins; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D009420:Nervous System / Q000254:growth & development*; D015398:Signal Transduction / Q000502:physiology
D029721:Drosophila Proteins; D053823:Hedgehog Proteins; D047908:Intracellular Signaling Peptides and Proteins; C077245:hh protein, Drosophila