Hypopituitarism caused by dysregulation of pituitary progenitors and epithelial to mesenchymal transition

MARÍA INÉS PÉREZ MILLÁN; BRINKMEIER ML; MORTENSEN AH; CAMPER SA

San Diego, CA

Congreso; Annual Meeting of The American Society of Human Genetics; 2014

Mutations in PROP1 and several other transcription factors, including POU1F1 (PIT1), HESX1, and OTX2, cause Multiple Pituitary Hormone Deficiency (MPHD) in humans and mice. PROP1 is co-expressed with stem cell markers including the growth factor receptor, GFRA2 and transcription factors SOX2, SOX9, and OCT4 (1, 2). In mouse fetal development Prop1 expression coincides spatially and temporally with the delamination, migration, and differentiation of progenitor cells in Rathke´s Pouch (RP) into hormone producing cells of the adenohypophysis. Prop1 mutant progenitors fail to undergo these processes, leading to organ dysmorphology, poor vascularization, and postnatal pituitary hypoplasia (3). Prop1 is necessary for regulating expression of two other MPHD genes; repressing Hesx1 and activating Pou1f1. Mutations in PROP1 are the most common known cause of MPHD, but most of the patients have no molecular diagnosis. The aim of this work is to identify additional downstream target genes of Prop1 to reveal new candidate genes for the cases of hypopituitarism that remain unexplained and to better understand the pathophysiology of MPHD. We chose an in vitro approach of identifying DNA sequences bound by PROP1 in an immortalized pituitary cell line by ChIP-Seq technology. Because the efficiency and specificity of ChIP depends on the quality of the antibody, we developed a biotin-tagged PROP1 system that permits precipitation of PROP1 with an avidin based detection assay. We identified enrichment of PROP1 binding at the Pou1f1 gene and in genes that encode components of the pathways of Cell Junction Signaling and Regulation of Epithelial Mesenchymal Transition. We examined expression of several candidate genes in Prop1 mutant mice and confirmed that their expression was altered. These data suggest that Prop1 promotes the transition of progenitors to differentiation by suppressing expression of progenitor markers like SOX genes and repressing claudin gene expression, in order to release tight junctions and permit EMT. In addition, Prop1 activates expression of cyclin E, a marker of the transition state, and Pou1f1, a marker of the differentiation state. This study establishes new mechanisms underlying PROP1?s role in pituitary progenitor cell regulation and offers new candidate genes for MPHD.