Test tube eye: completely, though not completely
How to grow an artificial eye
Kirill Stasevich, Compulenta
The scientific world is furiously discussing the latest news from Japan, and it's not about a rebellious atom at all: an artificial eye has been grown at the RIKEN Institute of Physico-Chemical Research. If we separate the essence of the work from the enthusiastic metaphors and sci-fi predictions accompanying it, we get the following.
In vertebrates, the eye is formed in a complex way. First, the embryos form a so–called eye bubble - an outgrowth on the anterior edge of the embryonic brain. Then the front wall of this bubble begins to bend inward until it meets the opposite wall (as if a balloon was pressed with a finger or palm and pressed until it stops – provided that it does not burst). The result is a goblet–shaped structure, which is called an eye glass. The bottom of this glass is two-layered. The outer layer, which is closer to the brain, is made up of retinal pigment cells: they provide the latter with nutrition and support. The inner layer is the cells of the retina itself; the layer is unusually complex and differentiated, contains different types of photosensitive neurons (known as rods and cones), accompanying glial cells, ganglion cells that carry a signal directly to the brain, and so on.
What did Japanese scientists do? They placed mouse embryonic cells in a special protein solution that directed their development towards the retina. (Recall that embryonic cells have a remarkable property: they can transform into any of more than 200 types of cells of an adult organism.)
Previous work in this direction was carried out, but the results were really not so impressive. Before that, biologists managed to get a frog embryo to form an eye in the wrong place – but in this case, the researchers processed a whole embryo, not a cell culture. Results were also obtained on the transformation of human embryonic cells into pigmented retinal feeding cells. Japanese scientists managed to make an eye glass: their embryonic cells grew in a special protein gel that mechanically supported the resulting structure.
The cells worked exactly as if they were not on the laboratory table, but in the embryo. First of all, they turned into the precursors of the retina and formed the same eye bubble within a week and a half. Then the eye bubble formed into an eye glass. Both layers of the walls and bottom of the glass began to rapidly differentiate according to their position – into pigment epithelial support cells or into photosensitive and light-conducting neurons. As the "eye" developed, the researchers were able to trace the stages of the transformation of the bubble into a glass. In a nutshell: those cells that were supposed to concave "relaxed" their cytoskeleton. Then the cells that were on the fold (they had to separate the outer and inner layer) acquired a wedge-shaped shape, as if indicating to their neighbors where to bend. Finally, the very deflection of the cell layer into the bubble was due to intensive division; due to the increase in the number of cells, the bubble wall had to bend - in the indicated direction.
Finally, the scientists decided to check whether the precursors of visual neurons obtained in this artificial visual glass are so correct. The cells of the inner wall of the glass were removed and placed in the same protein jelly, where they could form three-dimensional structures. And the cells formed six-layered structures with synapses, collectively characterizing the mature retina!
An article dedicated to this unique work has been published in the journal Nature (Self-organizing optic-cup morphogenesis in three-dimensional culture); the material is accompanied by many comments.
According to Yoshiki Sasai, one of the co-authors of the study, it remains to be seen whether such an artificial eye can perceive light and transmit information to the brain. However, previous work on the transplantation of the embryonic retina to adult rats was successful, which gives scientists hope for the "correctness" of their artificial eye. But even without this, the group obtained a fundamental result: it turns out that embryonic stem cells can form complex structures by themselves, relying only on the original program. They do not need constant pushing from the outside in the right direction.
Well, from a practical point of view, this is a huge step forward in the development of regenerative medicine, which already now in many cases allows not to treat diseased tissue with varying success (especially if this tissue is genetically diseased), but simply to replace it with healthy, grown "in vitro".
Prepared based on the materials of Nature News: Stem cells make 'retina in a dish'.
Portal "Eternal youth" http://vechnayamolodost.ru08.04.2011