Thyroid hormone regulates distinct paths to maturation in pigment cell lineages

Circulating endocrine factors are critical for orchestrating complex developmental processes during the generation of adult form. One such factor, thyroid hormone, regulates diverse cellular events during post-embryonic development and can drive disparate morphological outcomes through mechanisms that remain essentially unknown. We sought to define how thyroid hormone elicits opposite responses in the abundance of two pigment cell classes during development of the zebrafish adult pigment pattern. By profiling individual transcriptomes from thousands of neural crest derived cells, including pigment cells, we reconstructed developmental trajectories and identified lineage-specific changes in response to thyroid hormone. Contrary to our initial hypotheses for how TH differentially affects two related pigment cell lineages, we find instead that TH promotes the maturation of both melanophores and xanthophores in distinct ways, promoting cellular senescence and carotenoid accumulation, respectively. Our findings show that thyroid hormone and its receptors regulate distinct events of cellular maturation across lineages, and illustrate how a single, global factor integrates seemingly divergent morphogenetic outcomes across developmental time.