A regulatory loop involving PAX6, MITF, and WNT signaling controls retinal pigment epithelium development.
The separation of the optic neuroepithelium into future retina and retinal pigment epithelium (RPE) is a critical event in early eye development in vertebrates. Here we show in mice that the transcription factor PAX6, well-known for its retina-promoting activity, also plays a crucial role in early pigment epithelium development. This role is seen, however, only in a background genetically sensitized by mutations in the pigment cell transcription factor MITF. In fact, a reduction in Pax6 gene dose exacerbates the RPE-to-retina transdifferentiation seen in embryos homozygous for an Mitf null allele, and it induces such a transdifferentiation in embryos that are either heterozygous for the Mitf null allele or homozygous for an RPE-specific hypomorphic Mitf allele generated by targeted mutation. Conversely, an increase in Pax6 gene dose interferes with transdifferentiation even in homozygous Mitf null embryos. Gene expression analyses show that, together with MITF or its paralog TFEC, PAX6 suppresses the expression of Fgf15 and Dkk3. Explant culture experiments indicate that a combination of FGF and DKK3 promote retina formation by inhibiting canonical WNT signaling and stimulating the expression of retinogenic genes, including Six6 and Vsx2. Our results demonstrate that in conjunction with Mitf/Tfec Pax6 acts as an anti-retinogenic factor, whereas in conjunction with retinogenic genes it acts as a pro-retinogenic factor. The results suggest that careful manipulation of the Pax6 regulatory circuit may facilitate the generation of retinal and pigment epithelium cells from embryonic or induced pluripotent stem cells.
Mammalian Development Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, United States of America. kapilbharti@ninds.nih.gov
Kapil
K
Bharti
Melanie
M
Gasper
Jingxing
J
Ou
Martha
M
Brucato
Katharina
K
Clore-Gronenborn
James
J
Pickel
Heinz
H
Arnheiter
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D054338:Cell Transdifferentiation; D047108:Embryonic Development; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000378:metabolism; D018628:Gene Dosage; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor / Q000235:genetics / Q000378:metabolism; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012160:Retina / Q000254:growth & development* / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000254:growth & development* / Q000378:metabolism; D060449:Wnt Signaling Pathway / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; C405061:Dkk3 protein, mouse; D005136:Eye Proteins; D018398:Homeodomain Proteins; D036341:Intercellular Signaling Peptides and Proteins; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; C000605732:Pax6 protein, mouse; D012097:Repressor Proteins; C108526:fibroblast growth factor 15, mouse; D005346:Fibroblast Growth Factors