The process of understanding how to manipulate stem cells goes hand in hand with being able to coax them into forming more complex structures, recapitulating the path taken during the original development of the body when young. The state of the art at the present time is crude in comparison to what takes place in our bodies: the only way that researchers can presently obtain complex tissues is by using the extracellular matrix extracted from donor tissue as a guide for new growth. That guidance is as much chemical as structural, which is illustrated in the following recently announced research.
Researchers in Japan have grown a retina from mouse embryonic stem cells in a lab, but this isn't just another incremental advance in tissue engineering. Scientists claim their "retina in a dish" is by no small degree the most complex biological tissue yet engineered.
If the breakthrough can be adapted to work with human cells, it could provide a retina that is safe for transplantation into human eyes, providing a potential cure for many kinds of blindness. That's still years away, but in the meantime the lab-grown mouse tissue could provide researchers with a wealth of information on eye diseases and potential treatments for them.
Starting with the culture conditions they had established for retinal differentiation, the researchers added matrix proteins that they hoped would encourage the formation of the more rigid retinal epithelial structures. They then seeded the culture with mouse [embryonic stem] cells. Within a week, the cells began to form small vesicles and differentiate into two different tissue types: Cells on one side of the vesicles formed the mechanically rigid pigment epithelium, while cells on the other side differentiated into a more flexible tissue that folded inward in the shape of an embryonic optic cup - the retina's precursor.
As you can see, researchers remain a long way away from growing a transplant-ready human retina from cells alone - but this is still an important step forward in the path towards producing such a thing. What is learned here will also inform efforts to build the thousand other tissue types we'd like to be able to produce from scratch.