A novel function for Hedgehog signalling in retinal pigment epithelium differentiation.
Sonic hedgehog is involved in eye field separation along the proximodistal axis. We show that Hh signalling continues to be important in defining aspects of the proximodistal axis as the optic vesicle and optic cup mature. We show that two other Hedgehog proteins, Banded hedgehog and Cephalic hedgehog, related to the mouse Indian hedgehog and Desert hedgehog, respectively, are strongly expressed in the central retinal pigment epithelium but excluded from the peripheral pigment epithelium surrounding the ciliary marginal zone. By contrast, downstream components of the Hedgehog signalling pathway, Gli2, Gli3 and X-Smoothened, are expressed in this narrow peripheral epithelium. We show that this zone contains cells that are in the proliferative state. This equivalent region in the adult mammalian eye, the pigmented ciliary epithelium, has been identified as a zone in which retinal stem cells reside. These data, combined with double labelling and the use of other retinal pigment epithelium markers, show that the retinal pigment epithelium of tadpole embryos has a molecularly distinct peripheral to central axis. In addition, Gli2, Gli3 and X-Smoothened are also expressed in the neural retina, in the most peripheral region of the ciliary marginal zone, where retinal stem cells are found in Xenopus, suggesting that they are good markers for retinal stem cells. To test the role of the Hedgehog pathway at different stages of retinogenesis, we activated the pathway by injecting a dominant-negative form of PKA or blocking it by treating embryos with cyclopamine. Embryos injected or treated at early stages display clear proximodistal defects in the retina. Interestingly, the main phenotype of embryos treated with cyclopamine at late stages is a severe defect in RPE differentiation. This study thus provides new insights into the role of Hedgehog signalling in the formation of the proximodistal axis of the eye and the differentiation of retinal pigment epithelium.
Perron
Muriel
M
Laboratoire d'Embryologie Moléculaire, Bat. 445 Université Paris XI, 91405 Orsay, France. muriel.perron@emex.u-psud.fr
Boy
Sébastien
S
Amato
Marcos A
MA
Viczian
Andrea
A
Koebernick
Katja
K
Pieler
Tomas
T
Harris
William A
WA
D000818:Animals; D015415:Biomarkers; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005136:Eye Proteins; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D017403:In Situ Hybridization; D051762:PAX2 Transcription Factor; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D012097:Repressor Proteins; D015398:Signal Transduction / Q000502:physiology*; D013234:Stem Cells / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014704:Veratrum Alkaloids / Q000494:pharmacology; D014981:Xenopus / Q000033:anatomy & histology / Q000196:embryology* / Q000235:genetics; D029867:Xenopus Proteins
D015415:Biomarkers; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; C509232:IHH protein, Xenopus; D051762:PAX2 Transcription Factor; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; C000605732:Pax6 protein, mouse; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D014704:Veratrum Alkaloids; D029867:Xenopus Proteins; C000541:cyclopamine