Pten Regulates Retinal Amacrine Cell Number by Modulating Akt, Tgfβ, and Erk Signaling.
All tissues are genetically programmed to acquire an optimal size that is defined by total cell number and individual cellular dimensions. The retina contains stereotyped proportions of one glial and six neuronal cell types that are generated in overlapping waves. How multipotent retinal progenitors know when to switch from making one cell type to the next so that appropriate numbers of each cell type are generated is poorly understood. Pten is a phosphatase that controls progenitor cell proliferation and differentiation in several lineages. Here, using a conditional loss-of-function strategy, we found that Pten regulates retinal cell division and is required to produce the full complement of rod photoreceptors and amacrine cells in mouse. We focused on amacrine cell number control, identifying three downstream Pten effector pathways. First, phosphoinositide 3-kinase/Akt signaling is hyperactivated in Pten conditional knock-out (cKO) retinas, and misexpression of constitutively active Akt (Akt-CA) in retinal explants phenocopies the reduction in amacrine cell production observed in Pten cKOs. Second, Akt-CA activates Tgfβ signaling in retinal explants, which is a negative feedback pathway for amacrine cell production. Accordingly, Tgfβ signaling is elevated in Pten cKO retinas, and epistatic analyses placed Pten downstream of TgfβRII in amacrine cell number control. Finally, Pten regulates Raf/Mek/Erk signaling levels to promote the differentiation of all amacrine cell subtypes, which are each reduced in number in Pten cKOs. Pten is thus a positive regulator of amacrine cell production, acting via multiple downstream pathways, highlighting its diverse actions as a mediator of cell number control.



Despite the importance of size for optimal organ function, how individual cell types are generated in correct proportions is poorly understood. There are several ways to control cell number, including readouts of organ function (e.g., secreted hormones reach functional levels when enough cells are made) or counting of cell divisions or cell number. The latter applies to the retina, where cell number is regulated by negative feedback signals, which arrest differentiation of particular cell types at threshold levels. Herein, we show that Pten is a critical regulator of amacrine cell number in the retina, acting via multiple downstream pathways. Our studies provide molecular insights into how PTEN loss in humans may lead to uncontrolled cell division in several pathological conditions.
Departments of Biochemistry and Molecular Biology and Biological Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada.
Nobuhiko
0000-0002-8097-052X
N
Tachibana
Departments of Biochemistry and Molecular Biology and.
Robert
0000-0001-7819-2346
R
Cantrup
Departments of Biochemistry and Molecular Biology and Biological Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada.
Rajiv
R
Dixit
Departments of Biochemistry and Molecular Biology and Biological Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada.
Yacine
Y
Touahri
Departments of Biochemistry and Molecular Biology and.
Gaurav
0000-0002-0011-7503
G
Kaushik
Departments of Biochemistry and Molecular Biology and Biological Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada.
Dawn
D
Zinyk
Departments of Biochemistry and Molecular Biology and.
Narsis
0000-0001-5846-8739
N
Daftarian
Department of Comparative Biology and Experimental Medicine, Faculty of Veterinary Medicine, Alberta Children's Hospital Research Institute and Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N 4N1, Canada, and.
Jeff
0000-0002-0633-0698
J
Biernaskie
Cell Biology and Anatomy, Cumming School of Medicine, and.
Sarah
0000-0001-9880-9980
S
McFarlane
Departments of Biochemistry and Molecular Biology and Biological Sciences Platform, Sunnybrook Research Institute, Toronto, Ontario M4N 3M5, Canada cschuurm@sri.utoronto.ca.
Carol
C
Schuurmans
D000367:Age Factors; D025042:Amacrine Cells / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D002454:Cell Differentiation / Q000235:genetics; D049109:Cell Proliferation / Q000235:genetics; D004622:Embryo, Mammalian; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D000072041:PAX3 Transcription Factor / Q000235:genetics / Q000378:metabolism; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012160:Retina / Q000166:cytology / Q000196:embryology / Q000254:growth & development; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism
D000072041:PAX3 Transcription Factor; D016212:Transforming Growth Factor beta; C068686:Pax3 protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D051059:PTEN Phosphohydrolase; C487757:Pten protein, mouse
Erk; Pten; Tgfβ; amacrine cells; negative feedback signaling; retina