Differentiation of skeletal muscle from pituitary folliculo-stellate cells and endocrine progenitor cells.

We previously reported the ectopic differentiation of skeletal muscle cells in a pituitary gland transplanted beneath a kidney capsule. Morphological observation suggested that the skeletal muscle cells may have differentiated from folliculo-stellate (FS) cells in the anterior pituitary gland. However, at that time, we did not confirm this directly with an in vitro system. To obtain direct evidence, we used the Tpit/F1 cell line. The Tpit/F1 cell line was recently established from the pituitary gland of a temperature-sensitive T antigen transgenic mouse and has the characters of pituitary FS cells. Using Tpit/F1 cells, we have found that FS cells of the pituitary are able to differentiate into muscle cells in vitro. Additionally, we showed that the cells have some characteristics of pituitary FS cells and also express pituitary endocrine cell-specific transcription factor (pit-1) and prolactin genes, and can differentiate into striated muscle cells. The anterior pituitary gland is known to be of ectodermal origin, so the differentiation of its cells into striated muscle is completely unexpected. This is the first report of direct evidence of ectopic differentiation of skeletal muscle cells from pituitary cells.