The age-old question of where the “head” is on a starfish has been addressed in a new study conducted by researchers at Stanford University. Utilizing advanced genetic and molecular tools, the scientists created a 3D atlas of starfish gene expression, offering insights into the layout of their body regions. Unlike animals with a clear head-tail orientation, starfish exhibit a more distributed arrangement, with headlike regions found both in the center and along each limb of their bodies.
Laurent Formery, the lead author of the study and a postdoc at Stanford, expressed the unexpected complexity of the findings, stating, “The answer is much more complicated than we expected. It is just weird, and most likely the evolution of the group was even more complicated than this.”
The study focused on echinoderms, a group of animals that includes starfish and is closely related to humans. Unlike humans, starfish undergo a remarkable transformation from bilateral larvae, exhibiting symmetry across the midline, to adults with a distinct five-point star shape, known as a pentaradial body plan.
Christopher Lowe, a researcher at Hopkins Marine Station and senior author of the paper, emphasized the difficulty of comparing starfish anatomy to that of vertebrates. Traditional comparative studies rely on identifying similar structures in related groups of animals, but starfish present a challenge due to the lack of externally visible features akin to vertebrates.
To overcome this challenge, the researchers employed molecular techniques and genetic markers, such as Hox genes, to identify key genetic blueprints responsible for the body plan. This allowed them to investigate whether a molecular axis underlies starfish anatomy and plays a role in the development of their unique pentaradial body plan.
The team used RNA tomography, a technique revealing gene expression in tissue, and in situ hybridization, a method pinpointing specific RNA sequences in cells, to analyze the gene expression in sea star arms. By sectioning the arms into thin slices and reassembling them through computer models, the researchers created a 3D map of gene expression. The results showed headlike territories in the center of each arm and tail-like regions along the perimeter.
The study sheds light on the evolutionary complexity of starfish anatomy and challenges preconceived notions about their body plans. Formery noted the importance of considering a diverse range of animal phyla, emphasizing that life on Earth has evolved diverse solutions to fundamental biological problems over approximately 600 million years.
Lowe highlighted the significance of exploring modest animals that may not have spectacular nervous systems, as they likely represent early forms of life. The study underscores the power of a comparative approach that uses advanced genetic and molecular techniques to unravel the mysteries of biodiversity and evolutionary processes.