The face is an incredibly complex and personal structure that is built during embryonic development. One region of the embryo—called the extreme anterior domain—guides facial formation, recruiting cells from elsewhere to make the muscles, nerves, and bones that will comprise the face. Research in this field may help us diagnose and even repair craniofacial defects like cleft palate.
Hazel Sive : The face is the most profound part of our bodies in terms of identifying us as who we are, and in communicating how we’re feeling.
Justin Chen : The face is our portal to the world. So when you look at somebody, their facial expression, their non-verbal cues give you a lot of information. And so it’s really critical to have a functioning face to interact with the world.
Sive : How you get that enormously complicated personal structure, how it’s put together—you know, that is the driver.
We learn almost everything about human development by not studying humans—we study frogs.
Chen : The same tissue types that you find in a frog face are also found in a human face. And the lessons we learn in the frog embryo we can apply to humans.
Sive : So our lab looks at a part of the face, which becomes the mouth. The region becomes progressively thinner and thinner so that you just get a single layer of cells. And then we think that single layer of cells, which covers up where the mouth is going to open—gets pulled. And it breaks, which is the mouth. And making a hole in an animal is a very serious business because if it’s an uncontrolled hole, the animal has an injury. So the hole of the mouth has to be very carefully connected up to the digestive system.
But we also discovered something very surprising. Before the mouth actually forms, this part of the embryo—the extreme anterior domain—what it does is send out chemical signals that guide the formation of the rest of the face, that guide the other cells called neural crest cells that are going to build the face.
Chen : And those neural crest cells had to migrate into your face first, and then form all these different tissue types that would become the full-fledged face. So actually most of your face didn’t start off in your face. It started off at the top or behind your head a little bit. Before neural crest cells are in the face, the face is just a blank slate of tissue. And when the neural cells migrate and populate the blank slate, they actually form the 3D topography of your face.
Sive : It’s like a huge festival. It’s like an Ikea catalogue. There are all these instructions that are being followed, and you keep building things that are more and more complicated. But over time, this festival of Ikea building turns into this embryo with all its different parts.
Chen : And without the extreme anterior domain, the neural crest cells would be stuck up here, and wouldn’t be able to fully form your face and your mouth.
Sive : Part of our work is to try to understand how face formation goes wrong, and to know enough to contribute to try to correct it.
Chen : Craniofacial defects such as cleft palate make up about one third of all birth defects. Although it’s pretty common, the reason why these defects occur is not yet known. And so we hypothesize that the extreme anterior domain could be a factor. So if we could have a more detailed understanding of how the extreme anterior domain signals, we could maybe even diagnose craniofacial defects and be able to repair those defects in utero.
Sive : Every organism I look at that’s put together so beautifully and so perfectly, I think is just extraordinary. In my heart, the word is magical, and I think having the opportunity to understand the molecules behind the magic is a real privilege, and that’s what really drives our research.
- Video & Audio Production
- Ari Daniel
- Recording Assistance
- Brooke Havlik
- Production Assistance
- Sara Tewksbury
- © WGBH Educational Foundation 2016
- Additional Visuals
pexels.com/BRoll.io; Little Cloud Cinema; Oak & Rumble
- Special Thanks
- To NOVA, for your faces
- (main image: frog embryo section)
- Laura Jacox, Justin Chen & Hazel Sive