title: Rb-mediated neuronal differentiation through cell-cycle-independent regulation of E2f3a.
abstract: It has long been known that loss of the retinoblastoma protein (Rb) perturbs neural differentiation, but the underlying mechanism has never been solved. Rb absence impairs cell cycle exit and triggers death of some neurons, so differentiation defects may well be indirect. Indeed, we show that abnormalities in both differentiation and light-evoked electrophysiological responses in Rb-deficient retinal cells are rescued when ectopic division and apoptosis are blocked specifically by deleting E2f transcription factor (E2f) 1. However, comprehensive cell-type analysis of the rescued double-null retina exposed cell-cycle-independent differentiation defects specifically in starburst amacrine cells (SACs), cholinergic interneurons critical in direction selectivity and developmentally important rhythmic bursts. Typically, Rb is thought to block division by repressing E2fs, but to promote differentiation by potentiating tissue-specific factors. Remarkably, however, Rb promotes SAC differentiation by inhibiting E2f3 activity. Two E2f3 isoforms exist, and we find both in the developing retina, although intriguingly they show distinct subcellular distribution. E2f3b is thought to mediate Rb function in quiescent cells. However, in what is to our knowledge the first work to dissect E2f isoform function in vivo we show that Rb promotes SAC differentiation through E2f3a. These data reveal a mechanism through which Rb regulates neural differentiation directly, and, unexpectedly, it involves inhibition of E2f3a, not potentiation of tissue-specific factors.
authors.affiliation: Genetics and Development Division, Toronto Western Research Institute, University Health Network, University of Toronto, Ontario, Canada.
authors.forename: Danian
authors.initials: D
authors.lastname: Chen
authors.forename: Rene
authors.initials: R
authors.lastname: Opavsky
authors.forename: Marek
authors.initials: M
authors.lastname: Pacal
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Tanimoto
authors.forename: Pamela
authors.initials: P
authors.lastname: Wenzel
authors.forename: Mathias W
authors.initials: MW
authors.lastname: Seeliger
authors.forename: Gustavo
authors.initials: G
authors.lastname: Leone
authors.forename: Rod
authors.initials: R
authors.lastname: Bremner
mesh_terms: D025042:Amacrine Cells / Q000166:cytology* / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D002453:Cell Cycle; D002454:Cell Differentiation / Q000502:physiology; D017931:DNA Primers / Q000235:genetics; D050687:E2F1 Transcription Factor / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D050703:E2F2 Transcription Factor / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D050699:E2F3 Transcription Factor / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D005260:Female; D016161:Genes, Retinoblastoma; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008954:Models, Biological; D016160:Retinoblastoma Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050699:E2F3 Transcription Factor; C493754:E2f1 protein, mouse; C484940:E2f2 protein, mouse; D016160:Retinoblastoma Protein