Endocrine Abstracts

The pituitary derives from an invagination of the oral ectoderm, Rathke’s pouch, where pituitary progenitors are specified during early development. These progenitors are marked by expression of Sox2 and their entry into differentiation involves a switch from Sox2 to expression of other transcription factors implementing each of the lineage-specific differentiation programs. This switch is also accompanied by a switch in cell cycle control mechanisms that may be disrupted in pituitary tumors. Determination and maintenance of each pituitary lineage is dependent on a small number of the lineage-specific transcription factors. Whereas the mechanism for specification of the pituitary fate compared to oral ectoderm is still unknown, recent work has identified Pax7 as the pioneer transcription factor that specifies the intermediate lobe melanotrope fate. Pax7 achieves this through epigenetic mechanisms that ‘open’ about 2500 enhancers genom- wide. The interplay between the specification pioneer factor Pax7 and the POMC lineage determination factor Tpit will be discussed. The diversity of pituitary tumors reflect the composition of the normal gland with some tumors presenting with relatively well differentiated features and hormone secretion whereas others, the non-functioning adenomas, may reflect some progenitor or precursor states.