Genome variation in the trophoblast cell lifespan: Diploidy, polyteny, depolytenization, genome segregation

Histomorphometric comparison of the gravid and non-gravid uterus at the time of birth in the tammar wallaby (Macropus eugenii): insights into the embryo-maternal interface

Context Tammar wallabies have a very short gestation which does not exceed the length of the estrus cycle. Direct contact between embryo and mother is established via a short-lived yolk sac placenta only in the last third of gestation. Therefore, an efficient embryo-maternal interface is required to ensure rapid embryonic growth. However, the morphology of the placenta at the time of birth is not well described in marsupials. Aims To study the morphology of the embryo-maternal interface, to compare the gravid and the non-gravid uterus at the time of birth and to examine the presence of polyploid trophoblast cells. Methods Histomorphometrical analysis of the uteri from light microscopic images. Quantification of the endometrial vascularization in samples stained with CD31 using AI machine learning. DNA content estimations of the giant trophoblast cell nuclei by Feulgen Image Analysis Densitometry. Key results In histological sections of the gravid endometrium, more tissue area was occupied by blood vessels than in the non-gravid endometrium, with subepithelial capillaries making up one-fourth of the vessel area in the gravid endometrium. The gravid uterus exhibited a 2.75-fold increase in surface area due to winding folds. Polyploidy of the giant trophoblast cells was confirmed. Giant trophoblast cells showed signs of degeneration. Conclusions The adaptations of the gravid uterus and the polyploidy of the trophoblast cells ensure sufficient embryo-maternal exchange. However, they seem to be self-limiting. Implications Morphology of the tammar wallaby trophoblast and endometrium prior birth is optimized for rapid embryonic growth during the brief interaction between maternal and fetal cells but the placenta seemingly cannot persist after the designated due time.

"Mitotic Slippage" and Extranuclear DNA in Cancer Chemoresistance: A Focus on Telomeres

Mitotic slippage (MS), the incomplete mitosis that results in a doubled genome in interphase, is a typical response of TP53-mutant tumors resistant to genotoxic therapy. These polyploidized cells display premature senescence and sort the damaged DNA into the cytoplasm. In this study, we explored MS in the MDA-MB-231 cell line treated with doxorubicin (DOX). We found selective release into the cytoplasm of telomere fragments enriched in telomerase reverse transcriptase (hTERT), telomere capping protein TRF2, and DNA double-strand breaks marked by γH2AX, in association with ubiquitin-binding protein SQSTM1/p62. This occurs along with the alternative lengthening of telomeres (ALT) and DNA repair by homologous recombination (HR) in the nuclear promyelocytic leukemia (PML) bodies. The cells in repeated MS cycles activate meiotic genes and display holocentric chromosomes characteristic for inverted meiosis (IM). These giant cells acquire an amoeboid phenotype and finally bud the depolyploidized progeny, restarting the mitotic cycling. We suggest the reversible conversion of the telomerase-driven telomere maintenance into ALT coupled with IM at the sub-telomere breakage sites introduced by meiotic nuclease SPO11. All three MS mechanisms converging at telomeres recapitulate the amoeba-like agamic life-cycle, decreasing the mutagenic load and enabling the recovery of recombined, reduced progeny for return into the mitotic cycle.