Osteocytes in the American Alligator (Alligator mississippiensis)

Abstract

American alligators (Alligator mississippiensis) are a large crocodilian living in the southeastern United States of America. Compared to mammals, they have an extended growth period after reaching adulthood. Evolutionarily, they are also one of few vertebrates that have survived long geological periods with conservative morphology. Thus among many aspects related to the growth, development, and physiological adaptions of this long surviving species, the bone biology is interesting in terms of extended bone growth and maintenance, and especially the morphology and behavior of the osteons, the fundamental functional unit in the cortical bone. In this study, alligator bones were analyzed to visualize reptilian osteocytes and compare them to those of mice, the most commonly used mammalian model in bone biology and pharmaceutical studies. In the femora of a one‐year‐old alligator, the osteon structure of the cortical bone was studied to reveal the density and structure of osteons, as well as the morphology of osteocytes, using confocal imaging by Fluorescein Iso‐Thio‐Cyanate sample preparation and staining, and osteocyte morphology was visualized using acid‐etch SEM. Results demonstrated that in this relatively fast growing individual, there were few osteon‐like structures lined along the periosteum and endosteum, indicating a slow rate of bone remodeling. Compared to osteocytes in mice, osteocytes in the alligator specimen were irregular in shape and less evenly distributed, and had fewer dendrites. This study demonstrated the morphology of alligator osteocytes for the first time. The findings indicate that there are significant differences in bone morphology and physiology at the microstructural level between reptiles and mammals; the implications in our understanding of bone biology is yet to be fully understood. This study also suggests that American alligators will be an idea model for studying bone development, adaptation, and evolution at the pre‐mammalian stage.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.