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Lineage analysis reveals an endodermal contribution to the vertebrate pituitary

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Science  23 Oct 2020:
Vol. 370, Issue 6515, pp. 463-467
DOI: 10.1126/science.aba4767

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Origins of the pituitary gland

Placodes are specializations of the head ectoderm that are considered the source of many vertebrate novelties, including the nose, lens, ear, and hormone-producing portion of the pituitary. However, the presence of a pituitary-like structure in nonvertebrate chordates, derived instead from the endoderm, had suggested that the pituitary may predate placodes. Fabian et al. performed lineage tracing, time-lapse imaging, and single-cell messenger RNA sequencing to show that both endodermal and ectodermal cells can generate hormone-producing cells of the zebrafish pituitary. These experiments support that the vertebrate pituitary arises through interactions of an ancestral endodermal protopituitary with newly evolved placodal ectoderm.

Science, this issue p. 463

Abstract

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.

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