Stress Ball Morphogenesis in the Lungs of Gecko Lizards

Abstract

The evolution of primitive lungs millions of years ago was a key feature that facilitated the transition of some vertebrates from water to land. The divergence through time is reflected in the great morphological diversity of the lungs of extant tetrapods. Relative to more traditional model systems like mouse and chick, the reptilian lineage Squamata is highly overlooked in terms of research into lung structure and function, especially given their status as the taxonomic order of tetrapods with the most extant species. In 2021, a study elucidated a novel mechanism of organ development in the lungs of anole lizards. It was dubbed “stress ball morphogenesis” and is characterized by the development of a hexagonal meshwork of smooth muscle over the early-stage epithelial lumen of lizard lungs whose presence combined with increasing intralumenal pressure causes corrugations in the epithelium as it pokes through the gaps in the mesh. This study sought to determine whether or not this mechanism of development is present in the developing lungs of gecko lizards: the sister lineage to all extant squamates. Through immunofluorescence imaging at various stages of gecko lung development, we were able to provide evidence for the use of stress ball morphogenesis in shaping the epithelial corrugations in the lungs of the Gekkota. The principle of parsimony suggests that stress ball morphogenesis is an ancestral trait in squamates that has been conserved across the investigated lineages and presumably others. These results provide an evolutionary framework for future studies in the traits of lung development and general morphology of more derived squamates like chameleons and snakes.