Continuous model of conceptus implantation to the maternal endometrium

Abstract

As placental morphology as well as trophoblast characteristics exhibit wide diversity across mammalian species, underling molecules were also thought to vary greatly. In the majority of cases, however, regardless of the mode of implantation, physiological and biochemical processes in conceptus implantation to the maternal endometrium including the kinds of gene expression and their products are now considered to share many similarities. In fact, recent progress has identified that in addition to the hormones, cytokines, proteases and cell adhesion molecules classically characterized, molecules related to lymphocyte homing and epithelial-mesenchymal transition (EMT) are all required for the progression of conceptus implantation to placentation. In this review, therefore, the newest findings are all incorporated into the molecular and cellular events related to conceptus implantation to the maternal endometrium; primarily from non-invasive bovine placentation and also from invasive human implantation.

Uterine influences on conceptus development in fertility-classified animals

“…1), but is consistent with many other studies of beef and dairy heifers and cows (5,16,35,36,46,47). In the present study, embryonic loss in the SF heifers had to occur between days 17 and 28, which encompasses the implantation period of pregnancy (48)(49)(50). Recent data from dairy heifers and cows as well as somatic cell nuclear transfer pregnancies support the hypothesis that embryonic loss is most prevalent during this period (3,(51)(52)(53).…”

“…Recent data from dairy heifers and cows as well as somatic cell nuclear transfer pregnancies support the hypothesis that embryonic loss is most prevalent during this period (3,(51)(52)(53). However, little is known of the biological pathways and gene networks regulating implantation and placentation in cattle (49,52,54). Progesterone action via the endometrium is critical for conceptus development and elongation (14,24), and increased postovulatory progesterone concentrations are associated with increased conceptus growth on days 13 and 14 (55,56).…”

“…Differences in ECM remodeling were found in comparisons of the transcriptomes of chorionic, endometrial, or placental tissues from natural compared with embryo transfer or somatic cell nuclear transfer-derived pregnancies that are predominantly lost during implantation and placentation during the first few months (52). Implantation and placentation involve remodeling of the endometrial and chorionic ECM (49,76,77). Endometrial and fetal tissues undergo major tissue remodeling during this period to aid the proliferation, differentiation, and migration of binucleate cells, which are regulated by locally produced matrix metalloproteinases and tissue inhibitor of matrix metalloproteinase 1 (78)(79)(80)(81).…”

Promoting Roles of Embryonic Signals in Embryo Implantation and Placentation in Cooperation with Endocrine and Immune Systems

“…However, they also reduce attachment to the basement membrane, causing detachment of the epithelial cell layer that maintains embryo attachment. In contrast to the immune system, epithelial-mesenchymal transition (EMT) was reported to be involved in opening of the epithelial layer [84][85][86][87]. However, EMT simultaneously reduces the connection of epithelial cells to the basement membrane, undermining the anchoring foundation of the implanting embryo.…”

Abnormalities of placenta implantation

“…Abnormality of decidualization either by trauma or deficiency of decidua, as in cases of placenta previa implanting in the lower uterine segment or cesarean scar, is the common factor in the etiology of abnormal placentation. The pathogenesis seems to involve an abnormal interaction between the decidua and the invasive extravillous trophoblast, leading to a failure of maternal tissues to restrain the invading trophoblast . Multiple hypotheses have been raised to explain this abnormality.…”