title: Dicer is required for the maintenance of notch signaling and gliogenic competence during mouse retinal development.
abstract: MicroRNAs (miRNAs) are 19-25 nucleotide RNAs that regulate messenger RNA translation and stability. Recently, we performed a conditional knockout (CKO) of the miRNA-processing enzyme Dicer during mouse retinal development and showed an essential role for miRNAs in the transition of retinal progenitors from an early to a late competence state (Georgi and Reh [2010]: J Neurosci 30:4048-4061). Notably, Dicer CKO progenitors failed to express Ascl1 and generated ganglion cells beyond their normal competence window. Because Ascl1 regulates multiple Notch signaling components, we hypothesized that Notch signaling is downregulated in Dicer CKO retinas. We show here that Notch signaling is severely reduced in Dicer CKO retinas, but that retinal progenitors still retain a low level of Notch signaling. By increasing Notch signaling in Dicer CKO progenitors through constitutive expression of the Notch intracellular domain (NICD), we show that transgenic rescue of Notch signaling has little effect on the competence of retinal progenitors or the enhanced generation of ganglion cells, suggesting that loss of Notch signaling is not a major determinant of these phenotypes. Nevertheless, transgenic NICD expression restored horizontal cells, suggesting an interaction between miRNAs and Notch signaling in the development of this cell type. Furthermore, while NICD overexpression leads to robust glial induction in control retinas, NICD overexpression was insufficient to drive Dicer-null retinal progenitors to a glial fate. Surprisingly, the presence of transgenic NICD expression did not prevent the differentiation of some types of retinal neurons, suggesting that Notch inactivation is not an absolute requirement for the initial stages of neuronal differentiation.
authors.affiliation: Neurobiology and Behavior Program, Department of Biological Structure, School of Medicine, University of Washington, Seattle, USA.
authors.forename: Sean A
authors.initials: SA
authors.lastname: Georgi
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Reh
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000963:Antimetabolites / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D053487:DEAD-box RNA Helicases / Q000172:deficiency / Q000378:metabolism*; D003857:Deoxyuridine / Q000031:analogs & derivatives / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005136:Eye Proteins / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D009924:Organ Culture Techniques; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics; D051880:Receptors, Notch / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics; D012160:Retina / Q000187:drug effects / Q000254:growth & development*; D043244:Ribonuclease III / Q000172:deficiency / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D013105:Sphincterotomy, Transduodenal; D013234:Stem Cells / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000963:Antimetabolites; D001426:Bacterial Proteins; D004151:Dipeptides; D004791:Enzyme Inhibitors; D005136:Eye Proteins; D018398:Homeodomain Proteins; D008164:Luminescent Proteins; C419410:N-(N-(3,5-difluorophenacetyl)alanyl)phenylglycine tert-butyl ester; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; C000605732:Pax6 protein, mouse; D051880:Receptors, Notch; D012097:Repressor Proteins; C054562:yellow fluorescent protein, Bacteria; C509781:Dicer1 protein, mouse; D043244:Ribonuclease III; D053487:DEAD-box RNA Helicases; C031086:5-ethynyl-2'-deoxyuridine; D003857:Deoxyuridine