Neural Crest Cells Key to 500-Million-Year Evolution of the thyroid Gland
Table of Contents
A new study reveals how the acquisition of specialized stem cells drove the evolutionary leap from a primitive organ to the thyroid gland, offering insights into vertebrate development.
The thyroid, a critical regulator of metabolism and growth in vertebrates, didn’t emerge from whole cloth. Instead, research published on August 6 in Science Advances demonstrates that the evolution of this vital gland was facilitated by the incorporation of neural crest cells – a unique type of stem cell – into a precursor organ known as the endostyle. Researchers at the California institute of Technology used lamprey, a primitive fish, as a model organism to unravel this ancient evolutionary mystery.
Tracing the Roots of the Thyroid
For over 500 million years, the endostyle served as a foundational structure in chordates – the phylum encompassing all vertebrates. This organ, primarily involved in filter feeding, gradually transformed into the thyroid gland as vertebrates evolved.Understanding how this transition occurred has been a long-standing question in evolutionary biology.
The research team, led by Senior Postdoctoral Scholar Research Associate Jan Stundl and spearheaded by Marianne Bronner, the Edward B.Lewis professor of Biology and director of Caltech’s Beckman Institute, focused on the role of neural crest cells. Bronner’s lab has a long history of investigating these cells and their influence on vertebrate development, previously studying their involvement in the formation of structures like bony scales in sturgeon, heart tissue in zebrafish and chickens, and neurons in the lamprey’s peripheral nervous system.
Pro tip:- Neural crest cells seem to promote evolution. These cells appear capable of adapting more rapidly over evolutionary timescales than older, more established cell types.
The presence of neural crest cells in vertebrates, but not in invertebrates, further supports their role in driving the development of complex body plans.
Lamprey: A Window into the Past
The choice of lamprey as a model organism was strategic. Modern lamprey retain characteristics of the earliest vertebrates,including a functional endostyle. Researchers meticulously traced the development of the endostyle in lamprey, observing how neural crest cells contribute to the formation of its five distinct cell types, with two ultimately giving rise to thyroid follicles.
To confirm the crucial role of neural crest cells, the team employed the CRISPR gene-editing technology. By genetically deleting genes associated with neural crest cell development in lamprey embryos, they observed a dramatic outcome: the embryos failed to develop a fully formed endostyle. Instead, they exhibited a simplified, primitive lobe resembling the endostyle found in invertebrate chordates.
“Mother Nature is ‘smart,'” Stundl explained. “Rather than inventing something entirely new, evolution frequently enough repurposes existing structures. Neural crest cells appear to be key to enabling this process. Without them,we might still be filter feeders.”
Implications for Understanding Evolution
These findings underscore the power of cellular innovation in driving major evolutionary transitions. The research suggests that the acquisition of neural crest cells wasn’t simply an addition to the existing toolkit, but a catalyst for significant morphological change. The study highlights how evolution can work by “rebuilding” from existing components, rather than creating entirely new ones.
The research team included co-authors from Caltech, Uppsala University, and charles University in Prague, and was supported by funding from the National Institutes of Health, the European Union, Alex’s Lemonade Stand Foundation, the American heart Association, the Helen Hay Whitney Foundation, Swedish Research council Vetenskapsrådet, and the European Synchrotron radiation Facility. Bronner is also an affiliated faculty member with the Tianqiao and Chrissy Chen Institute for Neuroscience at Caltech.
