Vertebrate sensory organs arise from epithelial thickenings called placodes. Along with neural crest cells, cranial placodes are considered ectodermal novelties that drove evolution of the vertebrate head. The anterior-most placode generates the endocrine lobe [adenohypophysis (ADH)] of the pituitary, a master gland controlling growth, metabolism, and reproduction. In addition to known ectodermal contributions, we use lineage tracing and time-lapse imaging in zebrafish to identify an endodermal contribution to the ADH. Single-cell RNA sequencing of the adult pituitary reveals similar competency of endodermal and ectodermal epithelia to generate all endocrine cell types. Further, endoderm can generate a rudimentary ADH-like structure in the near absence of ectodermal contributions. The fish condition supports the vertebrate pituitary arising through interactions of an ancestral endoderm-derived proto-pituitary with newly evolved placodal ectoderm.

Columbia Stem Cell Initiative Department of Rehabilitation and Regenerative Medicine and Department of Genetics and Development Columbia University Irving Medical Center New York NY 10032 USA

Department of Stem Cell Biology and Regenerative Medicine Eli and Edythe Broad CIRM Center for Regenerative Medicine and Stem Cell Research W M Keck School of Medicine University of Southern California Los Angeles CA 90033 USA

Department of Zoology Charles University Prague Czech Republic

Graduate School of Biomedical Sciences Sanford Burnham Prebys Medical Discovery Institute La Jolla CA 92037 USA

Human Genetics Program Sanford Burnham Prebys Medical Discovery Institute La Jolla CA 92037 USA

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