title: The Akt signaling pathway is required for tissue maintenance and regeneration in planarians.
abstract: BACKGROUND
  Akt (PKB) is a serine threonine protein kinase downstream of the phosphoinositide 3-kinase (PI3K) pathway. In mammals, Akt is ubiquitously expressed and is associated with regulation of cellular proliferation, metabolism, cell growth and cell death. Akt has been widely studied for its central role in physiology and disease, in particular cancer where it has become an attractive pharmacological target. However, the mechanisms by which Akt signaling regulates stem cell behavior in the complexity of the whole body are poorly understood. Planarians are flatworms with large populations of stem cells capable of dividing to support adult tissue renewal and regeneration. The planarian ortholog Smed-Akt is molecularly conserved providing unique opportunities to analyze the function of Akt during cellular turnover and repair of adult tissues.
  
  
  RESULTS
  Our findings abrogating Smed-Akt with RNA-interference in the planarian Schmidtea mediterranea led to a gradual decrease in stem cell (neoblasts) numbers. The reduced neoblast numbers largely affected the maintenance of adult tissues including the nervous and excretory systems and ciliated structures in the ventral epithelia, which impaired planarian locomotion. Downregulation of Smed-Akt function also resulted in an increase of cell death throughout the animal. However, in response to amputation, levels of cell death were decreased and failed to localize near the injury site. Interestingly, the neoblast mitotic response was increased around the amputation area but the regenerative blastema failed to form.
  
  
  CONCLUSIONS
  We demonstrate Akt signaling is essential for organismal physiology and in late stages of the Akt phenotype the reduction in neoblast numbers may impair regeneration in planarians. Functional disruption of Smed-Akt alters the balance between cell proliferation and cell death leading to systemic impairment of adult tissue renewal. Our results also reveal novel roles for Akt signaling during regeneration, specifically for the timely localization of cell death near the injury site. Thus, Akt signaling regulates neoblast biology and mediates in the distribution of injury-mediated cell death during tissue repair in planarians.
authors.affiliation: Department of Molecular and Cell Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA, 95343, USA.|Quantitative and Systems Biology Graduate Program, University of California, Merced, CA, 95343, USA.
authors.forename: T Harshani
authors.initials: TH
authors.lastname: Peiris
authors.affiliation: Department of Molecular and Cell Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA, 95343, USA.|Quantitative and Systems Biology Graduate Program, University of California, Merced, CA, 95343, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Ramirez
authors.affiliation: Department of Molecular and Cell Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA, 95343, USA.|Quantitative and Systems Biology Graduate Program, University of California, Merced, CA, 95343, USA.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Barghouth
authors.affiliation: Department of Molecular and Cell Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA, 95343, USA. noviedo2@ucmerced.edu.|Quantitative and Systems Biology Graduate Program, University of California, Merced, CA, 95343, USA. noviedo2@ucmerced.edu.|Health Sciences Research Institute, University of California, Merced, CA, 95343, USA. noviedo2@ucmerced.edu.
authors.forename: Néstor J
authors.initials: NJ
authors.lastname: Oviedo
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D016923:Cell Death; D002454:Cell Differentiation; D049109:Cell Proliferation; D002923:Cilia / Q000378:metabolism; D015536:Down-Regulation; D004848:Epithelium / Q000378:metabolism; D009928:Organ Specificity; D010641:Phenotype; D010932:Planarians / Q000201:enzymology* / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference; D012038:Regeneration; D015398:Signal Transduction
chemical_list: D015415:Biomarkers; D051057:Proto-Oncogene Proteins c-akt
keywords: Akt; Planarians; Regeneration; Stem cells