Estrogen Signaling Drives Ciliogenesis in Human Endometrial Organoids.

The human endometrium is the inner lining of the uterus consisting of stromal and epithelial (secretory and ciliated) cells. It undergoes a hormonally regulated monthly cycle of growth, differentiation, and desquamation. However, how these cyclic changes control the balance between secretory and ciliated cells remains unclear. Here, we established endometrial organoids to investigate the estrogen (E2)-driven control of cell fate decisions in human endometrial epithelium. We demonstrate that they preserve the structure, expression patterns, secretory properties, and E2 responsiveness of their tissue of origin. Next, we show that the induction of ciliated cells is orchestrated by the coordinated action of E2 and NOTCH signaling. Although E2 is the primary driver, inhibition of NOTCH signaling provides a permissive environment. However, inhibition of NOTCH alone is not sufficient to trigger ciliogenesis. Overall, we provide insights into endometrial biology and propose endometrial organoids as a robust and powerful model for studying ciliogenesis in vitro.