Clump formation in mouse pituitary-derived non-endocrine cell line Tpit/F1 promotes differentiation into growth-hormone-producing cells.

The adenohypophysis comprises six types of endocrine cells, including PIT1-lineage cells such as growth hormone (GH)-producing cells and heterogeneous non-endocrine cells, such as pituitary stem/progenitor cells as a source of endocrine cells. We determine the expression of characteristic stem cell marker genes, including sex-determining region Y-box 2 (Sox2), in mouse pituitary-derived non-endocrine cell lines Tpit/E, Tpit/F1 and TtT/GF. We observed high expression of fibroblast growth factor (FGF) receptors in Tpit/F1 cells, which we characterised by cultivation in medium containing a basic FGF and B27 supplement as used for neural stem-cell differentiation. A 4-day cultivation of Tpit/F1 produced floating embryonic stem-cell-like clumps accompanied by a three-fold increase in Sox2 expression. Passages in these clumps maintained the proliferative activity and Sox2 expression levels. After 10 days of cultivation, Tpit/F1 cell clumps were immuno-positive for SOX2 and Ki67 (proliferation marker) and loosely attached to the well bottom. An additional 10 days of cultivation induced the emergence of GH-positive/pituitary-specific transcription factor (PIT1)-negative cells showing migration from the clumps. Pit1 overexpression in attached cells could not induce GH production. Finally, we confirmed the presence of PIT1-negative GH-producing cells (3.2-7.7 % of all GH-positive cells) in rat pituitary. Thus, we demonstrate that Tpit/F1 has the plasticity to differentiate into one type of hormone-producing cell.