Uterine RAC1 via Pak1-ERM signaling directs normal luminal epithelial integrity conducive to on-time embryo implantation in mice

Abstract

Successful embryo implantation requires functional luminal epithelia to establish uterine receptivity and blastocyst-uterine adhesion. During the configuration of uterine receptivity from prereceptive phase, the luminal epithelium undergoes dynamic membrane reorganization and depolarization. This timely regulated epithelial membrane maturation and precisely maintained epithelial integrity are critical for embryo implantation in both humans and mice. However, it remained largely unexplored with respect to potential signaling cascades governing this functional epithelial transformation prior to implantation. Using multiple genetic and cellular approaches combined with uterine conditional Rac1 deletion mouse model, we demonstrated herein that Rac1, a small GTPase, is spatiotemporally expressed in the periimplantation uterus, and uterine depletion of Rac1 induces premature decrease of epithelial apical-basal polarity and defective junction remodeling, leading to disrupted uterine receptivity and implantation failure. Further investigations identified Pak1-ERM as a downstream signaling cascade upon Rac1 activation in the luminal epithelium necessary for uterine receptivity. In addition, we also demonstrated that Rac1 via P38 MAPK signaling ensures timely epithelial apoptotic death at postimplantation. Besides uncovering a potentially important molecule machinery governing uterine luminal integrity for embryo implantation, our finding has high clinical relevance, because Rac1 is essential for normal endometrial functions in women. The implantation of the blastocyst into the maternal uterus is a crucial step in establishing pregnancy and thus ensuring further embryonic development. 1-3 Similar to many developmental processes, implantation involves an intricate succession of molecular and cellular interactions which must be executed within an optimal time frame. During this period, the acquisition of blastocyst implantation competency is synchronized with the establishment of uterine receptivity. [4][5][6] On the basis of previous findings, uterine sensitivity to implantationcompetent blastocysts is classically divided into three stages: pre-receptive, receptive and refractory phases. 7 In mice, prior to day 4 of pregnancy, the uterus is conventionally considered as the pre-receptive phase. On day 4 and beyond, the uterus becomes fully receptive following the priming actions of ovarian progesterone and preimplantation estrogen; whereas by late day 5, the uterus becomes refractory to initiate the implantation. 2,4,8 Upon entering the receptive phase, uterine luminal epithelium undergoes dynamic transformation. For example, on day 4 morning in mice, luminal epithelial cells cease proliferation under the dominance of increasing levels of ovarian progesterone and preimplantation estrogen. Meanwhile, the epithelial cells undergo differentiation, accompanied with a dynamic junction complex remodeling and membrane maturation, leading to a decrease of epithelial polarity approaching implantation and a cell-shape transition from...

Loci and pathways associated with uterine capacity for pregnancy and fertility in beef cattle

“…DOCK1 is a guanine nucleotide exchange factor for small Rho family G proteins; the encoded protein regulates the small GTPase Rac1, thereby influencing several biological processes including phagocytosis and cell migration [ 55 , 56 ]. Rac1 is involved in apoptotic clearance and epithelium development in mouse uterus [ 55 , 57 ]. In mice, conditional deletion of Rac1 resulted in implantation failure due to loss of uterine luminal epithelial integrity [ 57 ].…”

“…Rac1 is involved in apoptotic clearance and epithelium development in mouse uterus [ 55 , 57 ]. In mice, conditional deletion of Rac1 resulted in implantation failure due to loss of uterine luminal epithelial integrity [ 57 ].…”

“…One leading edge gene found in both the epithelial cell differentiation and epithelium development gene sets was TDRD7 , a strongly associated (p = 1.33 × 10 −7 ) GWAA positional candidate gene ( Table 1 ). Another leading edge gene in this gene set was Rac1 , which is essential for uterine luminal epithelial integrity and involved in embryo implantation in mice [ 55 , 57 ]. Depletion of uterine Rac1 during implantation elicited defective junction remodeling and epithelial polarity resulting in implantation failure in mice [ 57 ].…”

Rac1 modulates the formation of primordial follicles by facilitating STAT3-directed Jagged1, GDF9 and BMP15 transcription in mice

“…Rac1 belongs to the Rho family of small GTPases, which are important intracellular signaling proteins 47 . Evidence indicates that Rac1 is involved in many reproductive events, such as meiotic spindle stability and anchoring in oocytes 30 , embryo implantation 31 32 48 49 50 , and embryonic epithelial morphogenesis 33 . However, whether Rac1 plays a role in early folliculogenesis has not yet been reported.…”

Embryo–epithelium interactions during implantation at a glance

“…Depletion of uterine Rac1, which impairs receptivity (Tu et al, 2015), shifts the timing of alterations to the polarised epithelial phenotype with a reduction in the abundance of apical actin and of the cell junctional components PAR3 (also known as PARD3), occludin and claudin 7. Immunoreactivity to E-cadherin also appears increased, perhaps because it is concentrated in a shorter lateral domain.…”