CELLULAR AND MOLECULAR RESEARCH CENTER, SHAHID BEHESHTI MEDICAL UNIVERSITY, TEHRAN, IRAN
Introduction: Endometrial receptivity towards embryo implantation involves several dynamic changes, i.e. “the plasma membrane transformation of the luminal epithelium”. This includes the appearance of large projections on the apical surface of the epithelial cells, which their function(s) has not been clearly known in humans. This study is designed to identify the potential physiological roles of these projections (pinopods or uterodomes) during the human embryo implantation. Material and Methods: Endometrial biopsies from early, mid-, and late luteal phases of the menstrual cycle of 23 fertile female patients with regular menses were taken. To study the physiological function of human pinopods as biological markers of endometrial receptivity, scanning and transmission electron microscopies (SEM and TEM) as well as immunofluorescent and immunogold TEM were performed. Double- staining of light and electron microscopy were performed to detect leukemia inhibitory factor (LIF) and sintaxin-1, vesicle–associated membrane protein-2 (VAMP-2), and 25 kDa synaptosomal protein (SNAP-25) in order to identify their special correlation with human pinopods. Results: Pinopods (uterodomes) were abundant in the human endometrial glands. Morphological studies suggested secretory function for both the luminal and the glandular uterodomes. Images of immunostanings revealed co-localization of LIF with the specific markers of exocytosis. Conclusion: Uterodomes of human endometrium have secretory function, which is far from the pinocytotic role of pinopods of rodents.