title: Head regeneration in wild-type hydra requires de novo neurogenesis.
abstract: Because head regeneration occurs in nerve-free hydra mutants, neurogenesis was regarded as dispensable for this process. Here, in wild-type hydra, we tested the function of the ParaHox gsx homolog gene, cnox-2, which is a specific marker for bipotent neuronal progenitors, expressed in cycling interstitial cells that give rise to apical neurons and gastric nematoblasts (i.e. sensory mechanoreceptor precursors). cnox-2 RNAi silencing leads to a dramatic downregulation of hyZic, prdl-a, gsc and cnASH, whereas hyCOUP-TF is upregulated. cnox-2 indeed acts as an upstream regulator of the neuronal and nematocyte differentiation pathways, as cnox-2(-) hydra display a drastic reduction in apical neurons and gastric nematoblasts, a disorganized apical nervous system and a decreased body size. During head regeneration, the locally restricted de novo neurogenesis that precedes head formation is cnox-2 dependent: cnox-2 expression is induced in neuronal precursors and differentiating neurons that appear in the regenerating tip; cnox-2 RNAi silencing reduces this de novo neurogenesis and delays head formation. Similarly, the disappearance of cnox-2(+) cells in sf-1 mutants also correlates with head regeneration blockade. Hence in wild-type hydra, head regeneration requires the cnox-2 neurogenic function. When neurogenesis is missing, an alternative, slower and less efficient, head developmental program is possibly activated.
authors.affiliation: Department of Zoology and Animal Biology, University of Geneva, Sciences III, 30 Quai Ernest Ansermet, CH-1211 Geneva 4, Switzerland.
authors.forename: Marijana
authors.initials: M
authors.lastname: Miljkovic-Licina
authors.forename: Simona
authors.initials: S
authors.lastname: Chera
authors.forename: Luiza
authors.initials: L
authors.lastname: Ghila
authors.forename: Brigitte
authors.initials: B
authors.lastname: Galliot
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000235:genetics; D002454:Cell Differentiation / Q000235:genetics; D049109:Cell Proliferation; D015536:Down-Regulation; D018507:Gene Expression Regulation, Developmental; D006257:Head / Q000502:physiology; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D006829:Hydra / Q000235:genetics / Q000502:physiology*; D009420:Nervous System / Q000166:cytology / Q000254:growth & development*; D034622:RNA Interference; D012038:Regeneration / Q000235:genetics*
chemical_list: D018398:Homeodomain Proteins