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

Abstract

The lifespan of mammalian trophoblast cells includes polyploidization, its degree and peculiarities are, probably, accounted for the characteristics of placenta development. The main ways of genome multiplication-endoreduplication and reduced mitosis-that basically differ by the extent of repression of mitotic events, play, most probably, different roles in the functionally different trophoblast cells in a variety of mammalian species. In the rodent placenta, highly polyploid (512-2048c) trophoblast giant cells (TGC) undergoing endoreduplication serve a barrier with semiallogenic maternal tissues whereas series of reduced mitoses allow to accumulate a great number of low-ploid junctional zone and labyrinth trophoblast cells. Endoreduplication of TGC comes to the end with formation of numerous low-ploid subcellular compartments that show some signs of viable cells though mitotically inactive; it makes impossible their ectopic proliferation inside maternal tissues. In distinct from rodent trophoblast, deviation from (2ⁿ)c in human and silver fox trophoblast suggests a possibility of aneuploidy and other chromosome changes (aberrations, etc.). It suggests that in mammalian species with lengthy period of pregnancy, polyploidy is accompanied by more diverse genome changes that may be useful to select a more specific response to stressful factors that may appear occasionally during months of intrauterine development.

Keywords: Cell cycle, Endocycle, Polyploidy, Genome, Aneuploidy, Trophoblast, Placenta

Core tip: In rodent placenta, differentiation of secondary trophoblast giant cells give an example of the irreversible endoreduplication (up to 1024c and higher) that, however, results in formation of low-ploid subcellular compartments uncapable of mitotic proliferation. In the mammalian species with lengthy period of pregnancy, more diverse genome changes may be useful to select a more specific response to stressful factors that may appear occasionally during months of intrauterine development.