Gene Misexpression in a Smoc2+ve/Sox2-Low Population in Juvenile Prop1-Mutant Pituitary Gland

Mutations in the pituitary-specific transcription factor Prophet of Pit-1 (PROP1) are the most common genetic etiology of combined pituitary hormone deficiency (CPHD). CPHD is associated with short stature, attributable to growth hormone deficiency and/or thyroid-stimulating hormone deficiency, as well as hypothyroidism and infertility. Pathogenic lesions impair pituitary development and differentiation of endocrine cells. We performed single-cell RNA sequencing of pituitary cells from a wild-type and a Prop1-mutant P4 female mouse to elucidate population-specific differential gene expression. We observed a Smoc2+ve population that expressed low Sox2, which trajectory analyses suggest are a transitional cell state as stem cells differentiate into endocrine cells. We also detected ectopic expression of Sox21 in these cells in the Prop1 mutant. Prop1-mutant mice are known to overexpress Pou3f4, which we now show to be also enriched in this Smoc2+ve population. We sought to elucidate the role of Pou3f4 during pituitary development and to determine the contributions of Pou3f4 upregulation to pituitary disease by utilizing double-mutant mice lacking both Prop1 and Pou3f4. However, our data showed that Pou3f4 is not required for normal pituitary development and function. Double mutants further demonstrated that the upregulation of Pou3f4 was not causative for the overexpression of Sox21. These data indicate loss of Pou3f4 is not a potential cause of CPHD, and further studies may investigate the functional consequence of upregulation of Pou3f4 and Sox21, if any, in the novel Smoc2+ve cell population.