Developmental changes in the ploidy of mouse implanting trophoblast cells in vitro

Abstract

Shortly after the onset of implantation, polar mouse trophoblast cells proliferate and give rise to the ectoplacental cone, constituted by two distinct cell populations: undifferentiated, diploid cells and giant cells. Giant cells characteristically exhibit exaggerated dimensions and polyploid nuclei. In this study, we employ ectoplacental cones as a dynamic source of trophoblast giant cells to analyze cell proliferation, cell death, and ploidy under in vitro conditions. Our results show that DNA synthesis and the increase in the cell number are relevant only during the first 24 h of culture. Subsequently, DNA synthesis still occurs, mainly in the giant cell compartment, while the number of cells gradually decreases. Cell death by injury and apoptosis was also observed in the non-giant cell compartment of the ectoplacental cone. These findings suggest that the first 24 h of culture are crucial to the mitotic activity of the ectoplacental cone cells that gradually ceases, favoring the endoreduplication process. The DNA synthesis index during the subsequent experimental intervals emphasizes accumulation of DNA for the polyploidization. There was clear correlation between DNA content and nuclear dimension. The ploidy values for the trophoblast giant cells varied from 2C up to 368C in the giant cells, but were not as expressive as those known from in vivo conditions, probably due to the absence of regulatory factors specific to the embryonic-maternal interface. In situ hybridization and histochemistry for the nucleolusorganizing region showed that trophoblast nuclei have only two marker signals, indicative of a typical polytenic process. This present study elucidates important aspects of trophoblast behavior and provides new information on trophoblast physiology in vivo and in vitro.

The Causes and Consequences of Polyploidy in Normal Development and Cancer

“…Because no mitosis occurs between S phases, the replicated chromatids are not separated, so they form cohesin-linked polytene chromosomes similar to those of Drosophila salivary glands (Ilgren 1981). The endocycles have been proposed to accelerate TGC growth by shortening the cell cycle and simultaneously increasing the number of chromosomes (Gardner & Davies 1993, Gonçalves et al 2003.…”

The origins and functions of hepatic polyploidy

“…In mammals, endoreplication occurs when trophoblast stem cells (TSC) differentiate into trophoblast giant cells (TGC), which are required for embryo implantation [33]. The abbreviated cell cycle where S and G phases alternate has been proposed as a way to accelerate TGC growth [34]. Outside of development, endoreplication also occurs in response to DNA damage.…”

An imprinted GFP insertion reveals long-range epigenetic regulation in embryonic lineages

“…This reactivation in the D4 line has been hypothesized to reflect loss of imprinted X-inactivation in TGCs (Hadjantonakis et al, 2001). To determine whether this cell lineage shows a general defect in the maintenance of epigenetic silencing we analyzed the status of endogenous imprinted genes in TGCs differentiated from EPCs in vitro (Gonçalves et al, 2003;El-Hashash and Kimber, 2004). The distal Chr 7 imprinted genes H19, Igf2, and Cdkn1c exhibited normal imprinted expression in TGCs, and the H19 DMR (IC1) and KvDMR1 (IC2) maintained their normal allele-specific pattern of DNA methylation (Supplementary material, Fig.…”