Researchers have discovered an intriguing mechanism explaining the reduction and irregularity of emu wing bones. Not only are the wings notably shortened, but their skeletal components also exhibit an asymmetric fusion, which stems from a lack of muscle development in the wing’s distal areas.
Researchers have discovered an intriguing mechanism explaining the reduction and irregularity of emu wing bones. Not only are the wings notably shortened, but their skeletal components also exhibit an asymmetric fusion, which stems from a lack of muscle development in the wing’s distal areas. During their growth, this absence of muscle results in inadequate mechanical stress, which is essential for normal bone development. The research team found muscle progenitor cells with a unique dual identity, blending features of both somite[1]-derived myogenic and lateral plate mesoderm[2] cells. These cells undergo cell death during the formation of muscle, hindering the development of distal muscles. The study points out that variations in embryonic and fetal movements may significantly influence morphological evolution, providing insights into the intricate developmental processes that form skeletal structures.
Professor Mikiko Tanaka from the School of Life Science and Technology at the Institute of Science Tokyo, along with her colleagues, including Eriko Tsuboi and Ingrid Rosenburg Cordeiro (both former graduate students at Tokyo Institute of Technology) and current graduate student Satomi Ono, collaborated with Professor Shuji Shigenobu from the National Institute for Basic Biology, Professor Guojun Sheng from Kumamoto University, and Professor Masataka Okabe from Jikei University School of Medicine, to reveal a new mechanism behind the skeletal reduction and asymmetry of emu wings. Their findings show that the absence of muscle development in distal wings leads to a lack of mechanical stress during growth, causing the observed skeletal deformities. Moreover, the study unearthed muscle progenitor cells with a dual nature that experience cell death during muscle fiber differentiation, preventing appropriate muscle formation. This research indicates that differences in embryonic and fetal movements might be crucial in shaping anatomical features during evolution. These results will be published in Nature Communications on September 19, 2024.
Background
The emu is a bird that cannot fly, with wings that have significantly decreased in size. Despite their reduction, the specific mechanisms responsible for these changes have been largely unclear. In this study, the research group showed that the skeletal reduction in emu wings involves not just shortened bones but also asymmetrical bone fusion. They found that these skeletal abnormalities stem from the lack of muscle development in the distal wing areas, which leads to insufficient movement during growth—the very movement necessary for shaping the embryonic and fetal skeleton. Additionally, they discovered the presence of muscle progenitor cells in emu wings that combine traits of both somite-derived progenitor cells and lateral plate mesoderm cells. These cells undergo death during their transition into muscle fibers, resulting in inadequate muscle formation. Overall, the findings suggest that variations in embryonic and fetal movement can significantly influence the evolution of body structures.
Research Findings
The research team confirmed that emu wing bones are not only shorter but also exhibit considerable variation in shape and length among different individuals and even between the left and right wings of the same bird. This unique skeletal pattern relates to the lack of muscle development in their wings’ distal regions, leading to insufficient mechanical stress during bone development. Additionally, the study highlighted that the presence of muscle progenitor cells with dual identities—merging characteristics of somite-derived and lateral plate mesoderm cells—results in cell death during the formation of muscle fibers. This disruption in muscle development ultimately causes immobilization and subsequent skeletal deformities.
Societal Impact
This research emphasizes the vital role that embryonic and fetal movements play not only in the lengthening of skeletal elements but also in ensuring the symmetrical formation of bones. The findings reveal the significant consequences that inadequate embryonic movement, especially in the context of muscle formation issues like those seen in emus, can have on skeletal evolution. The study suggests that environmental factors affecting embryonic and fetal movement could have extensive implications for morphological evolution and diversity.
Future Directions
This research has highlighted the profound effects that embryonic and fetal movements can have on the evolution of skeletal structures. The team aims to explore how variations in these movements may influence skeletal evolution among different vertebrate species. This pioneering study opens new pathways for understanding how environmental aspects shape evolutionary morphology through their impact on embryonic and fetal movement.
Funding
This research was supported by JSPS KAKENHI Grant Numbers JP20H03301, JP17KT0106, MEXT KEKNHI JP18H04818, the NIBB Collaborative Research Program (21-357), and various foundations including the Astellas Foundation for Research on Metabolic Disorders, Mitsubishi Foundation, and Yamada Science Foundation to M.T.
Terms
- Somite: Block-like structures in the embryos of developing vertebrates, from which cells evolve to create muscles, bones, and skin dermis. Muscles of limbs are typically sourced from these somites.
- Lateral Plate Mesoderm: A section of the mesoderm that lies outward in the embryo, responsible for the development of limb buds, body walls, heart, and blood vessels.
