Generation of Functional GnRH-Responsive Pituitary-like Organoids from Ovine Embryonic Stem Cells.

The pituitary gland is a master regulator of endocrine and reproductive physiology; however, the lack of physiologically relevant in vitro models in livestock species has limited studies of pituitary development and endocrine function. Although pituitary organoids have been generated from human and mouse pluripotent stem cells, comparable models remain unavailable in large animal species. Here, we established functional pituitary-like organoids from ovine embryonic stem cells (oESCs) using a three-dimensional differentiation strategy. The resulting organoids self-organized into Rathke's pouch-like structures and acquired pituitary progenitor characteristics, as demonstrated by the robust expression of LHX3, PITX1, ISLET1 and PROP1. Compared with conventional two-dimensional differentiation, the organoids displayed enhanced structural organization and improved lineage specification. Notably, the organoids exhibited functional gonadotroph maturation, with GnRH treatment significantly upregulating FSHB and LHB expression, as confirmed by immunohistochemistry, qPCR and Western blot. SMART-Seq transcriptome analysis revealed progressive loss of pluripotency-associated signatures and activation of pituitary developmental programs, including sustained expression of lineage-associated regulators such as PAX6. Collectively, this study establishes the first ovine pituitary-like organoid model and demonstrates its capacity to generate functional GnRH-responsive gonadotroph cells. This platform provides a valuable resource for investigating pituitary development, reproductive endocrinology, livestock fertility, and endocrine disease mechanisms in a large-animal context.