Optogenetics is a relatively new biological technique that uses light to control the behaviour of cells in living tissue that have been genetically modified (using proteins) to become sensitive to light. Researchers at EMBL in Germany have now used this technique to induce tissue folding and shaping (morphogenesis) in a living embryo for the first time. The work could have implications for tissue engineering and regenerative medicine.
In their work, researchers led by Stefano de Renzis used optogenetics to reconstruct epithelial folding. This is a fundamental process in development in which cells move inwards and fold into the embryo (a process known as invagination), eventually producing internal tissues. They made use of a light-sensitive protein heterodimerization system that allowed them to control a particular protein, which, when present at the plasma membrane triggers a process called phosphorylation and activates a molecular motor called mysosin-II. When activated, this motor pulls on cortical actin filaments and makes the plasma membrane contract.
“The protein we made light sensitive is the enzyme RhoGEF2, which activates the small GTPase Rho1,” explains de Renzis. “Rho1 then activates a signalling cascade and activates the molecular motor myosin-II. We employed a technique called two-photon illumination, which is very precise because we can activate volumes as small as a femtolitre.”
Surprisingly, we found that we could induce invagination in tissues that normally do not undergo this process by simply activating Rho signalling and apical constriction,” he tells Physics World. “Rho signalling in fact transforms specific chemical inputs into mechanical forces and being able to control this signal pathway and induce morphogenesis in a living embryo was a real thrill for us.
“Equally interesting was the fact that we could make cells and tissues respond in a different way and form into various shapes by modulating the frequency and power of the light. This gave us the feeling of being in total control of morphogenesis. Until now, we had to let the embryo ‘reveal’ its behaviour to us, but now it appears that we can actually start to guide it.”
Towards a synthetic embryo?
The researchers did their experiments on developing fruit flies (Drosophila) but de Renzis says that the technique described in this study could also be applied to other organisms and even ex vivo stem cell cultures. “In this case, optogenetics could be ideal for reconstructing and directing tissue development and be used to re(build) artificial tissue in regenerative medicine,” he explains.
The team, reporting its work in Nature Communications 9 2366, says that it is now focusing on reconstructing embryonic development in “mutant” embryos that would otherwise not undergo morphogenesis. “Looking longer term, we would like to build a synthetic embryo,” reveals de Renzis. “Can we engineer patterning systems up to the point that we can completely guide embryonic development?”