Taken together, we show that there are distinct processes by which different squamate species build their lungs. Notably, the luminal pressure-driven stress ball morphogenesis in anoles appears to be derived, potentially due to the fact anoles develop in ovo so much faster than other squamates!

Notably, these structures aren’t being sculpted by smooth muscle like in mammal lungs. Rather, they are enriched for pMLC in the apical region of the epithelium, suggesting an apical-constriction mediated outgrowth. This developmental process is what bird lungs use to branch!

We also found some very interesting aspects of chameleon lung development. Chameleon lungs exhibit multiple chambers and these bizarre projections called diverticulae. These chambers and diverticulae seem to grow out via concentrated cell proliferation.

We decided to computationally simulate our hypothesized process: anoles expand their epithelium via luminal pressure while chams and geckos expand their epithelium via proliferation. This simulation suggested the epithelium would be thinner in anole lungs, and sure enough, that’s what we found!

This suggests geckos and chams don’t drastically increase luminal pressure to push the epithelium through the smooth muscle. EdU shows more cell proliferation in the epithelium of gecko and cham lungs than anoles, suggesting proliferation pushes the epithelium through the mesh in geckos and chams.

What we found in leopard gecko and chameleon lungs was also consistent in our opportunistic sampling of Italian wall lizard embryos.

We found that smooth muscle meshes show up in all three species, but what is really striking are the differences in inflation between anoles and the other two species. Aspect ratios are significantly different through development of the anole lung, but not in leopard geckos or chameleons.

We aimed to investigate whether stress ball morphogenesis is conserved in other squamates. Additionally, we wanted to see if more complex lungs exhibit distinct patterns of lung morphogenesis. To do this, we looked at embryonic lungs of leopard geckos, brown anoles, and veiled chameleons!

Lungs are strikingly diverse and they formed in distinct ways between species. M Palmer previously showed that anoles generate their bumpy, balloon-like lungs via luminal pressure pushing the epithelium through a smooth muscle mesh (i.e. stress ball morphogenesis).

www.science.org/doi/10.1126/...

Collaboration with the stellar past/present members of the @celestemnelson.bsky.social and @mallarinolab.bsky.social labs!

I'll also be looking to recruit an MS student to study the functional morphology and biomechanics of adhesion, friction, and/or locomotion in sea urchins, geckos, or anoles! Please share! @sicb-dcb-dvm.bsky.social @sicb.bsky.social