Male Brown anole displaying dewlap |
A new study from Princeton University shows how the brown anole lizard solves one of nature’s most complex problems — breathing — with elegant simplicity. Whereas human lungs develop over months and years into baroque tree-like structures, the anole lung develops in just a few days into crude lobes covered with bulbous protuberances. These gourd-like structures, while far less refined, allow the lizard to exchange oxygen for waste gases just as human lungs do. And because they grow quickly by leveraging simple mechanical processes, anole lungs provide new inspiration for engineers designing advanced biotechnologies.
“Our group is really interested in understanding lung development for engineering purposes,” said Celeste Nelson, the Wilke Family Professor in Bioengineering and the principal investigator of a study published in the journal Science Advances. “If we understand how lungs build themselves, then perhaps we can take advantage of the mechanisms mother nature uses to regenerate or engineer tissues.”
While avian and mammalian lungs develop great complexity through endless branching and complicated biochemical signaling, the brown anole lung forms its relatively modest complexity through a mechanical process the authors likened to a mesh stress ball — the common toy found in desk drawers and DIY videos. This study is the first to look at the development of a reptile lung, according to the researchers.
The anole lung starts a few days into development as a hollow, elongated membrane surrounded by a uniform layer of smooth muscle. During development, the lung cells secrete fluid, and as they do so the inner membrane slowly inflates and thins like a balloon. The pressure pushes against the smooth muscle, causing it to tighten and spread apart into fiber bundles that ultimately form a honeycomb-shaped mesh. Fluid pressure continues pushing the stretchy membrane outward, bulging through the gaps in the sinewy mesh and forming fluid-filled bulbs that cover the lung. Those bulges create lots of surface area where the gas exchange occurs.