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FACTEURS IMPLIQUES DANS LA DIFFERENCIATION ET LA TRANSDIFFERENCIATION DE L'EPITHELIUM CORNEEN

Abstract : General questions about mechanisms in differentiation of corneal epithelium are experimentally addressed: Is the lens required for its induction? Is keratin12 (K12), which is considered to be a cornea-specific keratin, also expressed in other tissues except cornea? What are the respective roles of the eye master gene Pax6, versus other genes coding for diffusible proteins in the corneal stroma?
In early chick embryos, Pax6 is expressed in the nuclei not only in the developing eye tissues, but also in other head epithelia such as nasal and oral epithelia. After corneal epithelium individualization, Pax6 continues to be expressed through all the embryonic stage and the life of the adult, whereas it is downregulated until no more expressed after 7 days of incubation in the other head epithelia. K12 expression is strongly detectable in the cytoplasm of the corneal epithelium from a late embryonic stage, 14 days in chick, 21 days in rabbit, and throughout all the life of the adult. However, no matter of the species, there is no K12 expression detected in the nasal and oral epithelia.
I transfected cDNA coding for an active form of Pax6 (coupled to the VP16 activator) into 2.5 to 3 day chick embryos by in ovo electroporation. This leads to abnormal orientation of the pre-existing developing eye showing the importance of the amount and distribution of Pax6 transcripts, but not to the formation of ectopic eye structure.
I examined the role of the lens in the differentiation of the corneal epithelium by removing the invaginating lens vesicle in chick embryo. In contrast to what has been previously published, we find that the lens is required only for the general growth of the eye, but not for cornea differentiation, neither stromal fibroblasts migration, nor epithelial K12 expression.
To address the question whether the stroma plays a role in Pax6 and subsequently K12 expression, I performed several types of epithelial / mesenchymal recombinations. The recombinants were grafted under the kidney capsule of nude mice. Experiments performed with avian tissues showed that Pax6 can be downregulated and chick corneal epithelium directly transformed into an epidermis and subsequently form feathers when associated to a dermis, but only before 5 days of development. In collaboration with Dr. David Pearton, we showed that in contrast, in mammals, Pax6 can be downregulated even in an adult corneal epithelium. Moreover, in the latter case, its transdifferentiation into an epidermis is undirect and process via the formation of epidermal appendages, i.e. hairs.
Because there are insufficient donor for cornea grafting, it was important to know whether a reverse transformation was possible. Initially using chick embryo, I associated corneal stroma with mouth and nasal epithelia, or dorsal epidermis, or Pax6 electroporated epidermis and I found that corneal stroma can not transform these embryonic epithelia into corneal epithelium even after Pax6 electroporation.
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Contributor : Ying Yang <>
Submitted on : Tuesday, April 4, 2006 - 12:03:25 PM
Last modification on : Friday, November 6, 2020 - 3:46:30 AM
Long-term archiving on: : Monday, September 17, 2012 - 1:20:17 PM

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  • HAL Id : tel-00012079, version 1

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Ying Yang. FACTEURS IMPLIQUES DANS LA DIFFERENCIATION ET LA TRANSDIFFERENCIATION DE L'EPITHELIUM CORNEEN. Médicaments. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨tel-00012079⟩

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