The dynamics of uterine endometrium is important for successful establishment and maintenance of embryonic implantation and development, along with extensive cell differentiation and proliferation. The tissue event is precisely and complicatedly regulated as several signaling pathways are involved including two main hormones, estrogen and progesterone signaling. We previously showed a novel signaling molecule, Serine/threonine protein kinase 3/4 (STK3/4), which is responded to hormone in the mouse uterine epithelium. However, the role and regulation of its target, YES-associated protein (YAP) remains unknown. In this study, we investigated the expression and regulation of YAP in mouse endometrium. We found that YAP was periodically expressed in the endometrium during the estrous cycle. Furthermore, periodic expression of YAP was shown to be related to the pathway under hormone treatment. Interestingly, estrogen was shown to positively modulate YAP via endometrial epithelial receptors. In addition, the knockdown of YAP showed that YAP regulated various target genes in endometrial cells. The knockdown of YAP down-regulated numerous targets including ADAMTS1, AMOT, AMOTL1, ANKRD1, CTNNA1, MCL1. On the other hand, the expressions of AREG and AXL were increased by its knockdown. These findings imply that YAP responds via Hippo signaling under various intrauterine signals and is considered to play a role in the expression of factors important for uterine endometrium dynamic regulation.

The uterus is essential for embryo implantation and fetal development. During the estrous cycle, the uterine endometrium undergoes dramatic remodeling to prepare for pregnancy. Angiogenesis is an essential biological process in endometrial remodeling. Steroid hormones regulate the series of events that occur during such remodeling. Researchers have investigated the potential factors, including angiofactors, involved in endometrial remodeling. The Hippo signaling pathway discovered in the 21st century, plays important roles in various cellular functions, including cell proliferation and cell death. However, its role in the endometrium remains unclear. In this review, we describe the female reproductive system and its association with the Hippo signaling pathway, as well as novel Hippo pathway genes and potential target genes.

Objective: This study aimed to examine the influence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on pregnancy in cytokeratin-18 (K18)-hACE2 transgenic mice.Methods: To determine the expression of hACE2 mRNA in the female reproductive tract of K18-hACE2 mice, real-time polymerase chain reaction (RT-PCR) was performed using the ovary, oviduct, uterus, umbilical cord, and placenta. SARS-CoV-2 was inoculated intranasally (30 μL/mouse, 1×104 TCID50/mL) to plug-checked K18-hACE2 homozygous female mice at the pre-and post-implantation stages at 2.5 days post-coitum (dpc) and 15.5 dpc, respectively. The number of implantation sites was checked at 7.5 dpc, and the number of normally born pups was investigated at 20.5 dpc. Pregnancy outcomes, including implantation and childbirth, were confirmed by comparison with the non-infected group. Tissues of infected mice were collected at 7.5 dpc and 19.5 dpc to confirm the SARS-CoV-2 infection. The infection was identified by performing RT-PCR on the infected tissues and comparing them to the non-infected tissues.Results: hACE2 mRNA expression was confirmed in the female reproductive tract of the K18-hACE2 mice. Compared to the non-infected group, no significant difference in the number of implantation sites or normally born pups was found in the infected group. SARS-CoV-2 infection was detected in the lungs but not in the female reproductive system of infected K18-hACE2 mice.Conclusion: In K18-hACE2 mice, intranasal infection with SARS-CoV-2 did not induce implantation failure, preterm labor, or miscarriage. Although the viral infection was not detected in the uterus, placenta, or fetus, the infection of the lungs could induce problems in the reproductive system. However, lung infections were not related to pregnancy outcomes.

The uterus is an important hormone-responsive tissue in the female reproductive system. Histologically, the uterus is comprised of three layers, including the perimetrium, myometrium, and endometrium. Among them, the endometrium has an essential function in embryo implantation and development to achieve successful gestation. It is the innermost layer of the uterus which consists of both luminal and glandular epithelial and stromal cells. In mammals, the uterine endometrium undergoes a dynamic cyclical growth and tissue remodeling controlled by the ovarian hormones, estrogen, and progesterone during the menstrual (human) and the estrous (rodent) cycle (Evans et al., 1990; Dharma et al., 2001; Wood et al., 2007). This dynamic remodeling involves the recurrent synchrony of cell proliferation, differentiation, and apoptosis, along with extracellular matrix (ECM) turnover, leukocyte infiltration, and angiogenesis (Evans et al., 1990). Estrogen is usually known to induce endometrium growth by thickening the mucosa during the follicular phase (Groothuis et al., 2007). On the other hand, progesterone blocks estrogen-induced endometrial growth and transforms it into a receptive state for blastocyst implantation. Classically, estrogen regulates the expression of an array of genes to mediate its major actions on uterine cells via its nuclear receptors, ERα and ERβ. On the other hand, progesterone regulates its actions on the uterine via progesterone receptor (PR), PR-A, and PR-B in the uterus (Mulac-Jericevic & Conneely, 2004).

In mice, the uterus undergoes dynamic changes regulated by estrogen and progesterone during the estrous cycle. Proper regulation of these changes is critical for successful pregnancy. The Family with sequence similarity 3 (Fam3) gene family, comprising Fam3a, Fam3b, Fam3c, and Fam3d, encodes cytokine-like proteins, but their uterine roles remain unclear. This study examined Fam3 expression in the mouse uterus across the estrous cycle and assessed estrogen-dependent regulation. RNA-seq analysis revealed increased Fam3b, Fam3c, and Fam3d expression during proestrus and estrus. Notably, Fam3d showed dynamic regulation, peaking in these stages. To test estrogen regulation, estradiol was administered to ovariectomized mice, showing maximal Fam3d expression at 24 h post-injection. ERα antagonist treatment blocked this induction, indicating ERα-mediated regulation. Immunofluorescence localized FAM3D to the cytoplasm of luminal and glandular epithelia, especially in the apical region, with no stromal or nuclear expression. These findings suggest that estrogen and Erα (Estrogen receptor alpha) signaling control Fam3d expression, implicating FAM3D in uterine epithelial function. This study provides novel insights into Fam3d’s role in uterine physiology and a foundation for exploring its function in reproduction.