http://www.nature.com/nature/journal/v4 ... 2042a.html
https://www.econologie.info/share/partag ... qQAE5v.pdf
We are starting to be able to form the shape of an eye from a stem cell !!
Reality is much more interesting than fiction !!
In particular the conditions which make it possible to reconstitute an organ, ultra-easy in plants, but much more complex for animals !!
Elucidation of the underlying mechanisms
embryonic eye development
REGENERATIVE MEDICINE
diy eyes
In this issue, Eiraku et al. 1 provide a series of extraordinary videos recording the formation
of an embryonic mouse eye: for the first time, we see unfolding in real time the beautiful events that shape the early stages of mammalian eye development. But even more remarkable is that these are not recordings
from live animals, but of self-organizing three-dimensional (3D) cultures of embryonic stem cells.
By the sixth week of human development, the rudiments of the mature eye are visible: bilayered optic cups, partially encapsulating the lens vesicles, have formed from the eye-field region of the anterior neural plate and the overlying surface ectoderm (Fig. 1) . From the inner layer of the cup, the complex laminar structure of the neural retina will develop, with light-sensing photoreceptor cells connecting through interneurons to the retinal ganglion cells whose axonal processes project to the higher visual centers in the brain.
Elucidation of the underlying mechanisms
embryonic eye development began more
51than a century ago. In one of his most significant
experiments, Hans Spemann, a founder of developmental biology, showed that if the optic vesicle (the structure that eventually evolves into the optic cup) is destroyed, the lens fails to form. The interaction of the surface
ectoderm (from which the lens derives) with the underlying optic vesicle has been considered a classical example of embryonic induction - the process by which one cell group signals to a neighboring group and influences their future development. An array of genes has now been identified, many of which encode transcription factors or growth factors that are essential for the formation of the optic cup.
Generation of complex organs in vitro is a major challenge in regenerative medicine. But it is not an impossible one: an entire synthetic retina has now been generated from embryonic stem cells. See Article p.51than a century ago. In one of his most significant
experiments, Hans Spemann, a founder of developmental biology, showed that if the optic vesicle (the structure that eventually evolves into the optic cup) is destroyed, the lens fails to form. The interaction of the surface
ectoderm (from which the lens derives) with the underlying optic vesicle has been considered a classical example of embryonic induction - the process by which one cell group signals to a neighboring group and influences their future development. An array of genes has now been identified, many of which encode transcription factors or growth factors that are essential for the formation of the optic cup.
The likelihood of growing a complex organ such as an eye in a dish, however, has seemed remote and futuristic, although this remote frontier of regenerative medicine constantly moves closer. In the past decade, inspiring work2 has shown that expression of eye-field transcription factors can lead to eye formation
in unusual locations along the body of
Xenopus frogs. Moreover, following the
generation of human embryonic stem (ES) cells, it has proved possible 3,4 to direct their differentiation towards the retinal lineage and generate both retinal pigmented epithelium
(RPE) and retinal neurons (Fig. 1). Cell-
culture approaches have mainly sought to maximize the development of specific cell types with the potential aim of transplanting such cells for therapeutic purposes.
In vitro, RPE cells derived from ES cells self-organize into a characteristic simple monolayer. By contrast, reproducing the more complex and precise laminar organization of the neural retina presents a difficult tissue-engineering challenge. But reports describing lens-like structures5 and retinal progenitor rosettes in ES-cell cultures6 hinted at some potential for organization of eye tissue in vitro.
Now, Eiraku et al. 1 (page 51) reveal with startling beauty and remarkable clarity that the complex process of evagination of the optic vesicle, and then its invagination to form the bilayered cup, can occur spontaneously
in culture, starting with a population of homogeneous pluripotent cells - cells that can
differentiate into any cell type (see Fig. 1 of the paper1 and the supplementary videos).
The key to this advance was that Eiraku and colleagues did not just just simplify their previous7
differentiation protocol for ES cultures, but also added Matrigel, which includes extracellular-matrix components. Under these conditions, and using a green fluorescent protein
(GFP) reporter gene expressed in the eye field and the neural retina, they found that a neuro-epithelium-like layer of GFP-positive cells evaginated from the sides of hollow balls of ES cells, in a process reminiscent of optic-vesicle formation . Over time, the optic vesicles spontaneously underwent dynamic morphogenesis
and formed two-layered cups.
