Abstract
How does mucin MUC20 expression change during the menstrual cycle in different cell types of human endometrium? Study involved examination of MUC20 expression in two previously published RNA-seq datasets in whole endometrial tissue (n = 10), sorted endometrial epithelial (n = 44) or stromal (n = 42) cell samples. RNA-Seq results were validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR) in whole tissue (n = 10), sorted epithelial (n = 17) and stromal (n = 17) cell samples. MUC20 protein localization and expression were analysed in human endometrium by immunohistochemical analysis of intact endometrial tissue (n = 6) and also Western blot of cultured stromal and epithelial cells (n = 2). MUC20 is differentially expressed in the endometrium between the pre-receptive and receptive phases. We show that MUC20 is predominantly expressed by epithelial cells of the receptive endometrium, both at the mRNA (RNA-Seq, P = 0.005; qRT-PCR, P = 0.039) and protein levels (Western blot; immunohistochemistry, P = 0.029). Our results indicate MUC20 as a novel marker of mid-secretory endometrial biology. We propose a model of MUC20 function in the hepatocyte growth factor (HGF)-activated mesenchymal-epithelial transition (MET) receptor signalling specifically in the receptive phase. Further investigations should reveal the precise function of MUC20 in human endometrium and the possible connection between MUC20 and HGF-activated MET receptor signalling. MUC20 could potentially be included in the list of endometrial receptivity markers after further clinical validation.
Highlights
Successful implantation of a blastocyst to the maternal endometrium is one of the key events during embryonic development
Our study has identified increased MUC20 expression in the receptive endometrium epithelium, and we propose it as a new promising biomarker candidate of endometrial receptivity that needs to be validated further to prove its ability to define the window of implantation (WOI)
We detected a significant increase in MUC20 expression during the transition from the pre-receptive to the receptive phase of the endometrium
Summary
Successful implantation of a blastocyst to the maternal endometrium is one of the key events during embryonic development. Endometrial tissue cells that respond to hormonal regulation interact with the blastocyst only during a short period during the normal endometrial maturation – 5-6 days after fertilisation (Hertig et al, 1956), which is referred to as a window of implantation (WOI) or a receptivity phase (Psychoyos, 1986). The surface of the endometrial epithelium is the site where the first molecular interactions occur between the trophoblast cells of the implanting embryo and the maternal organism (Enders et al, 1983). Assisted reproductive technologies have been widely used during the last decades, the rate of successful pregnancies among patients who had passed in vitro fertilisation (IVF) procedure has not remarkably risen. The ability to define the WOI more precisely would significantly improve the pregnancy rate of the IVF procedure
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