Endocrine Abstracts

JOINT1497

The transcription factor PROP1 is necessary to trigger the onset of pituitary development by promoting the differentiation of stem cells into hormone-producing cell lineages by an epithelial-to-mesenchymal transition-like (EMT-like) process. Biallelic loss of function mutations in PROP1 cause deficiencies in growth hormone, thyroid stimulating hormone, and prolactin. PROP1 target genes have been identified, but little is known about interacting protein partners. We genetically engineered mouse pituitary GHTF1 cells to express biotin-tagged PROP1 and performed Rapid Immunoprecipitation and Mass spectrometry Experiments (RIME) to identify PROP1 interacting proteins. From 43 candidate proteins detected, we selected Nuclear Factor I/B (NFIB) for further studies based on the role of this gene family (NFIA, NFIB, NFIC, and NFIX) in development of other tissues. This family plays a role in developing the central nervous system, lungs, hair follicles, and skeletal muscle tissue. Notably, NFIB is involved in promoting EMT in various types of cancer. Using immunostaining, we observed that the pattern of NFIB and NFIA expression during mouse pituitary development was similar to SOX2 from e12.5 to e16.5. NFIB and NFIA also colocalized early on (e12.5) with PROP1. NFIB and NFIA have overlapping function in some organ systems and biallelic loss of function causes embryonic lethality. Thus, we generated a pituitary-specific knockout mice of Nfib and Nfia:Hesx1Cre/+; Nfia_Flox/Flox; Nfib_Flox/Flox. At postnatal day 1 these mice have an increase in the number of alpha-GSU and TSH-positive cells (with normal corticotrophs and somatotrophs). The stem cell population expressing SOX2 was not different between mutant and controls. We found increased double-positive GH and TSH-producing cells, suggesting that NFIB and/or NFIA are required to maintain proper cell lineage differentiation during pituitary organogenesis. Together, our findings expose NFIA/NFIB as important factors for pituitary lineage confinement. Further research is needed to understand the molecular mechanisms underlying these processes.