Morphological Characterization of Basally Located Uninucleate Trophoblast Cells as Precursors of Bovine Binucleate Trophoblast Giant Cells

Abstract

Binucleate trophoblast giant cells (TGCs) are one characteristic feature of the ruminant placenta. In cows, the frequency of TGCs remains constant for most of the duration of pregnancy. As TGCs are depleted by their fusion with uterine epithelial cells, they need to be constantly formed. It is still unclear whether they develop from stem cells within the trophectoderm or whether they can arise from any uninucleate trophoblast cell (UTC). Within the latter, generally accepted theory, a basally located uninucleate cell (BUC) without contact to the feto-maternal interface would represent a transient cell between a UTC and a TGC. So far, no evidence for the existence of such transient cells or for the presence of stem cells has been shown. The aim of the present study is to morphologically characterize the early stages of TGC development. Placentomal tissue of 6 pregnant cows from different gestational stages (gestational days 51–214) was examined for BUCs, UTCs, and TGCs either in serial sections (light and transmission electron microscopy, TEM, n = 3), in single sections (TEM, n = 2), or by serial block face-scanning electron microscopy (n = 1). These investigations revealed the occurrence of BUCs, as well as young TGCs showing contact with the basement membrane (BM), but without apical contact to the feto-maternal interface. The study morphologically defines these 2 cell types as early stages of TGC development and shows that binucleation of TGCs can precede detachment from the BM.

Exosomes derived from placental trophoblast cells regulate endometrial epithelial receptivity in dairy cows during pregnancy

“…In ruminants, embryo implantation begins on day 16 of gestation, the binuclear trophoblast giant cells form on day 17 of embryo development, and the process of implantation is completed on day 22 [30,31] . During the first 3 months after implantation, the binucleated trophoblast giant cells continued to fuse with the endometrial epithelial cells and played a placental regulatory role [6] .…”

“…: SYXK (JING) 2015-0004). The cells were isolated as described previously [ 6 ]. In particular, the fetal cotyledons were aseptically separated from the maternal caruncles and divided into 1 mm 3 sections, which were then dispersed into a 10 cm 2 dish (430167; Corning Incorporated, Corning, NY, USA) and cultured in a 37°C incubator (Forma-371; Thermo Scientific, Waltham, MA, USA) for 30 min until the sections conglutinated on the dish.…”

“…In mammalian fetuses, the placenta, a transient organ, plays a critical role in improving fetomaternal interaction by ensuring adequate fetal oxygen and nutrient supply throughout the entire pregnancy, and determining the success of embryo implantation and pregnancy outcomes [ 2 , 3 , 4 ]. In bovine placenta, trophoblasts form a barrier between the mother and the fetus [ 5 , 6 ]. Thus, understanding how obstetric diseases can be avoided and how the pregnancy rate can be increased during the first trimester and pregnancy is necessary for assessing the functions of trophoblasts.…”

Ruminant Placental Adaptation in Early Maternal Undernutrition: An Overview

“…Binucleated cells constitute ~20% of the total population, and their migration and fusion with maternal endometrial cells generate foeto-maternal syncytia and consequently promote implantation and placentome formation. Along with their structural role, binucleated cell functions include hormone production, such as placental lactogen and steroid hormones ( 23 , 26 ).…”

Evolution of placentation in cattle and antelopes

“…Since they migrate to and fuse with the uterine epithelium, the population of BNCs requires continual renewal. In their early developmental stages, BNCs of cattle retain contact with the basal membrane of the trophoblast (Attiger et al, 2018). This raises the possibility that BNCs arise by mitosis of basally located stem cells rather than being derived from uninucleate trophoblast cells (Attiger et al, 2018).…”