Trophoblast differentiation during the transition from trophoblastic plate to lacunar stage of implantation in the rhesus monkey and human

Abstract

The transition from the trophoblastic plate stage to the early lacunar stage was examined in a series of implantation sites from the rhesus monkey, timed on the basis of the preovulatory estrogen peak, and prepared for transmission electron microscopy. This transition was compared with specimens from stage 5a, b, and c in the Carnegie collection of human embryos. The transition was marked by the differentiation of a new type of syncytial trophoblast--namely, a unilaminar microvillous polarized syncytium, which developed throughout the trophoblastic plate, forming characteristic intrasyncytial clefts. The rapid development of this type of syncytium created a nonclotting chamber for maternal blood wherever trophoblast intrusion into maternal vessels created confluence. Although the nature of the material in the Carnegie series precluded cytological characterization of the trophoblast, there is evidence that a similar transition occurs in human trophoblast and that in the human also the appearance of lacunae marks a change from an early invasive trophoblast to a situation in which growth is more significant.

Vulnerability of primitive human placental trophoblast to Zika virus

“…Unfortunately, this period of early pregnancy is poorly studied because of the lack of available human tissue. Most of what is known has come from older literature (68)(69)(70), archived samples (71), and from analogies drawn from histological studies on nonhuman primates (71)(72)(73). As the primate embryo implants, a penetrating mass of invasive STB forms in the implantation zone and soon surrounds the conceptus.…”

The Macaque Placenta—A Mini-Review

“…During the period of blood vessel invasion, clusters of syncytial trophoblasts coalesce and expand laterally to form a trophoblastic plate (Enders 2007). The nature of the syncytial trophoblasts changes from an invasive one to a type more suited for absorption and transfer (Enders 1989) by their microvillous surface. In the majority of these trophoblasts, intrasyncytial clefts will be formed around day 11.…”

“…As the ultimate goal, reproduction is preceded by implantation of the blastocyst within the endometrium and the development of a placenta. This placentation process is extensively described for humans; literature on monkey placentation is less common, although some excellent papers are available (Carter and Enders 2004;Enders et al 1985;Enders, 1989Enders, , 1993Enders, , 2000Enders, , 2007Ramsey et al 1976). Comparative evaluations of different species demonstrate the existence of a significant variety in all the steps of the placental process and in its morphological structures.…”

Chorionic gonadotrophin and embryo-maternal recognition during the peri-implantation period in primates

“…It is now apparent (Surani et ai, 1990) that neither the male nor the female genome by itself is totipotential. Surani et al (1990) (1988) The presence of the ß-subunit of CG was detected in 3 of seven 6-8 cell human embryos by in-situ hybridization (Bonduelle et ai, 1988 (Enders, 1989), but, after the mature chorionic villi have formed, CG expression is restricted to the syncytiotrophoblast. The co-ordinated expression of both subunits for the secretion of biologically active CG, together with the timing of such secretion and its physiological role within the embryo, at the embryo-endometrial interface or in trophoblast penetration, have yet to be clarified.…”

“…Implantation is highly invasive and interstitial in man and the apes, but relatively superficial in monkeys (simians) Hertig & Rock, 1945;Hendrickx & Enders, 1980;Enders et ai, 1983;Moore et ai, 1985;Hearn & Summers, 1986;Smith et ai, 1987;Hearn et ai, 1988a, b, in press; Enders, 1989). Therefore, the morphology of implantation is now relatively well described for a few primate species, showing a similar general pattern, albeit with distinct species differences (Hearn, 1986).…”