title: Ethanol-induced microphthalmia is not mediated by changes in retinoic acid or sonic hedgehog signaling during retinal neurogenesis.
abstract: BACKGROUND
  Microphthalmia (reduced eye size), generally accompanied by vision defects, is a hallmark of fetal alcohol spectrum disorder (FASD) in humans. In zebrafish, embryonic ethanol exposure over the time of retinal neurogenesis also results in microphthalmia. This microphthalmia is in part the consequence of reduced retinal cell differentiation, including photoreceptors. Here we pursue 2 signaling pathways implicated in other aspects of FASD pathogenesis: retinoic acid (RA) and Sonic hedgehog (Shh).
  
  
  METHODS
  We evaluated markers for RA and Shh signaling within the eyes of embryos treated with ethanol during the period of retinal neurogenesis. We also performed rescue experiments using administration of exogenous RA and microinjection of cholesterol, which augments Shh signaling.
  
  
  RESULTS
  Using sequential or co-treatments, RA did not rescue ethanol-induced microphthalmia at any concentration tested. In addition, RA itself caused microphthalmia, although the underlying mechanisms were distinct from those of ethanol. Interestingly, RA treatment appeared to recover photoreceptor differentiation in a concentration-dependent manner. This may be an independent effect of exogenous RA, as ethanol treatment alone did not alter RA signaling in the eye. Cholesterol injection also did not rescue ethanol-induced microphthalmia at any concentration tested, and ethanol treatments did not alter expression of shh, or of ptc-2, which is normally regulated by Shh signaling.
  
  
  CONCLUSIONS
  Together these findings indicate that, during the time of retinal neurogenesis, effects of ethanol on eye development are likely independent of the RA and Shh signaling pathways. These studies suggest that FASD intervention strategies based upon augmentation of RA or Shh signaling may not prevent ethanol-induced microphthalmia.
authors.affiliation: Department of Biological Sciences, University of Idaho, Moscow, Idaho 83844-3015, USA.
authors.forename: Bhavani
authors.initials: B
authors.lastname: Kashyap
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Frey
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Stenkamp
mesh_terms: D000014:Abnormalities, Drug-Induced / Q000378:metabolism / Q000473:pathology; D000165:Acridine Orange / Q000378:metabolism; D000818:Animals; D002492:Central Nervous System Depressants / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D004625:Embryo, Nonmammalian / Q000187:drug effects / Q000378:metabolism; D000431:Ethanol / Q000633:toxicity*; D005260:Female; D053823:Hedgehog Proteins / Q000378:metabolism*; D008850:Microphthalmos / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D055495:Neurogenesis; D012160:Retina / Q000196:embryology* / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D019076:Transgenes; D014212:Tretinoin / Q000378:metabolism* / Q000494:pharmacology / Q000633:toxicity; D014815:Vitamins / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity; D015027:Zebrafish / Q000196:embryology / Q000235:genetics / Q000378:metabolism
chemical_list: D002492:Central Nervous System Depressants; D053823:Hedgehog Proteins; D014815:Vitamins; D000431:Ethanol; D014212:Tretinoin; D000165:Acridine Orange