title: Dynamic Pax6 expression during the neurogenic cell cycle influences proliferation and cell fate choices of retinal progenitors.
abstract: BACKGROUND
  The paired homeobox protein Pax6 is essential for proliferation and pluripotency of retinal progenitors. However, temporal changes in Pax6 protein expression associated with the generation of various retinal neurons have not been characterized with regard to the cell cycle. Here, we examine the dynamic changes of Pax6 expression among chicken retinal progenitors as they progress through the neurogenic cell cycle, and determine the effects of altered Pax6 levels on retinogenesis.
  
  
  RESULTS
  We provide evidence that during the preneurogenic to neurogenic transition, Pax6 protein levels in proliferating progenitor cells are down-regulated. Neurogenic retinal progenitors retain a relatively low level of Pax6 protein, whereas postmitotic neurons either elevate or extinguish Pax6 expression in a cell type-specific manner. Cell imaging and cell cycle analyses show that neurogenic progenitors in the S phase of the cell cycle contain low levels of Pax6 protein, whereas a subset of progenitors exhibits divergent levels of Pax6 protein upon entering the G2 phase of the cell cycle. We also show that M phase cells contain varied levels of Pax6, and some correlate with the onset of early neuronal marker expression, forecasting cell cycle exit and cell fate commitment. Furthermore, either elevating or knocking down Pax6 attenuates cell proliferation and results in increased cell death. Reducing Pax6 decreases retinal ganglion cell genesis and enhances cone photoreceptor and amacrine interneuron production, whereas elevating Pax6 suppresses cone photoreceptor and amacrine cell fates.
  
  
  CONCLUSIONS
  These studies demonstrate for the first time quantitative changes in Pax6 protein expression during the preneurogenic to neurogenic transition and during the neurogenic cell cycle. The results indicate that Pax6 protein levels are stringently controlled in proliferating progenitors. Maintaining a relatively low Pax6 protein level is necessary for S phase re-entry, whereas rapid accumulation or reduction of Pax6 protein during the G2/M phase of the cell cycle may be required for specific neuronal fates. These findings thus provide novel insights on the dynamic regulation of Pax6 protein among neurogenic progenitors and the temporal frame of neuronal fate determination.
authors.affiliation: Jules Stein Eye Institute and Department of Ophthalmology, Molecular Biology Institute, University of California, David Geffen School of Medicine, Stein Plaza, Los Angeles, CA 90095, USA. evanhsieh07@gmail.com
authors.forename: Yi-Wen
authors.initials: YW
authors.lastname: Hsieh
authors.forename: Xian-Jie
authors.initials: XJ
authors.lastname: Yang
mesh_terms: D000367:Age Factors; D000818:Animals; D001973:Bromodeoxyuridine / Q000378:metabolism; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology*; D016923:Cell Death / Q000235:genetics / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D002642:Chick Embryo / Q000166:cytology; D053595:Embryonic Stem Cells / Q000502:physiology*; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry / Q000379:methods; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009419:Nerve Tissue Proteins / Q000378:metabolism; D055495:Neurogenesis / Q000502:physiology*; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D034622:RNA Interference / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000166:cytology* / Q000196:embryology; D014162:Transfection / Q000379:methods
chemical_list: D005136:Eye Proteins; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D000071841:PAX6 Transcription Factor; C000605730:PAX6 protein, human; D051761:Paired Box Transcription Factors; D018809:Proliferating Cell Nuclear Antigen; D012097:Repressor Proteins; D001973:Bromodeoxyuridine
references.citation: Dev Biol. 2006 Apr 15;292(2):486-505
references.pmid: 16464444
references.citation: J Morphol. 1951 Jan;88(1):49-92
references.pmid: 24539719
references.citation: Annu Rev Neurosci. 1997;20:483-532
references.pmid: 9056723
references.citation: Development. 1988;103 Suppl:115-9
references.pmid: 3250848
references.citation: Neuron. 1990 Jun;4(6):833-45
references.pmid: 2163263
references.citation: Mech Dev. 1997 Jun;64(1-2):111-26
references.pmid: 9232602
references.citation: J Hered. 2005 May-Jun;96(3):171-84
references.pmid: 15653558
references.citation: Cell. 2001 Apr 6;105(1):43-55
references.pmid: 11301001
references.citation: Dev Cell. 2005 Apr;8(4):565-74
references.pmid: 15809038
references.citation: Development. 2001 Mar;128(6):943-57
references.pmid: 11222148
references.citation: Acta Neuropathol. 1993;86(2):126-35
references.pmid: 8213068
references.citation: Genes Cells. 1996 Jan;1(1):11-5
references.pmid: 9078363
references.citation: Cell Growth Differ. 1995 Dec;6(12):1531-40
references.pmid: 9019158
references.citation: Gene. 1991 Dec 15;108(2):193-9
references.pmid: 1660837
references.citation: Cell. 1996 Jul 12;86(1):71-82
references.pmid: 8689689
references.citation: Genesis. 2009 Mar;47(3):175-87
references.pmid: 19208436
references.citation: Development. 2007 Apr;134(7):1311-22
references.pmid: 17329367
references.citation: Development. 1999 Jan;126(2):383-95
references.pmid: 9847251
references.citation: Development. 2004 Dec;131(24):6131-40
references.pmid: 15548580
references.citation: Development. 2006 Jun;133(11):2201-10
references.pmid: 16672338
references.citation: Dev Biol. 2007 Jul 15;307(2):498-520
references.pmid: 17509554
references.citation: Nat Genet. 2004 Jan;36(1):31-9
references.pmid: 14702038
references.citation: Development. 2000 Oct;127(20):4325-34
references.pmid: 11003833
references.citation: Nature. 1987 Jul 9-15;328(6126):131-6
references.pmid: 3600789
references.citation: Science. 1988 Mar 4;239(4844):1142-5
references.pmid: 2449732
references.citation: Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):5515-20
references.pmid: 11960009
references.citation: Invest Ophthalmol Vis Sci. 2007 Dec;48(12):5408-19
references.pmid: 18055787
references.citation: Proc Natl Acad Sci U S A. 2002 May 14;99(10):6812-5
references.pmid: 11983873
references.citation: Dev Biol. 2007 May 15;305(2):659-73
references.pmid: 17399698
references.citation: Dev Biol. 1999 Jan 1;205(1):79-97
references.pmid: 9882499
references.citation: Invest Ophthalmol Vis Sci. 2002 Nov;43(11):3522-9
references.pmid: 12407164
references.citation: Nat Rev Neurosci. 2001 Feb;2(2):109-18
references.pmid: 11252990
references.citation: Nature. 1991 Dec 19-26;354(6354):522-5
references.pmid: 1684639
references.citation: Nat Genet. 1992 Nov;2(3):232-9
references.pmid: 1345175
references.citation: Science. 1995 Mar 24;267(5205):1788-92
references.pmid: 7892602
references.citation: Dev Biol. 1998 Jul 15;199(2):185-200
references.pmid: 9698439
references.citation: Development. 2002 Oct;129(19):4535-45
references.pmid: 12223410
references.citation: Nat Genet. 1994 Aug;7(4):463-71
references.pmid: 7951315
references.citation: Development. 2008 Dec;135(24):4037-4047
references.pmid: 19004853
references.citation: Curr Opin Cell Biol. 2001 Dec;13(6):706-14
references.pmid: 11698186
references.citation: BMC Dev Biol. 2008 May 28;8:59
references.pmid: 18507827
references.citation: Science. 1994 Aug 5;265(5173):785-9
references.pmid: 7914031
references.citation: Development. 2002 Jan;129(2):455-66
references.pmid: 11807037
references.citation: J Embryol Exp Morphol. 1986 Sep;97:95-110
references.pmid: 3794606
references.citation: Proc Natl Acad Sci U S A. 1996 Jan 23;93(2):589-95
references.pmid: 8570600
references.citation: Biochem Biophys Res Commun. 1997 Nov 7;240(1):196-202
references.pmid: 9367909
references.citation: Mol Vis. 2001 Jan 02;7:1-5
references.pmid: 11172136
references.citation: Development. 1999 Oct;126(19):4213-22
references.pmid: 10477290
references.citation: Neuron. 1988 Mar;1(1):15-26
references.pmid: 3272153
references.citation: Dev Biol. 2007 Feb 1;302(1):50-65
references.pmid: 16979618