Everything we thought we knew about where thyroid cells come from was wrong, solving a massive mystery in how mammals evolved.
bioRxiv · March 13, 2026 · 10.64898/2026.03.11.710917
Why it matters
For decades, textbooks taught that the thyroid’s hormone-producing C-cells came from the neural crest, a separate embryonic source. By mapping individual cell trajectories, researchers proved they actually develop from the same gut lining as the rest of the thyroid, explaining how these two distinct cell types successfully merge into one organ.
From the abstract
The thyroid has a remarkable evolution, appearing first as an integral presumably exocrine constituent of the chordate endostyle that is transformed into an endocrine gland during metamorphosis in basal vertebrates. In mammals, the thyroid acquires a second endocrine cell type, calcitonin-producing C-cells, which for long were inferred a neural crest origin, shuttled to the embryonic thyroid by the ultimobranchial bodies. However, recent lineage tracing experiments firmly establish these neuroen