Dynamics of polyploidization and quantitative studies of Ag-NORs in the interphase nucleoli of cambial trophoblast cells in the developing rat placenta

Megamitochondria Initiate Differentiation of Monolayer Cells into Detached Dome Cells That Proliferate by a Schizogony-Like Amitotic Process

“…Figure7(a) depicts chromatin coming back into focus for light microscopy approximately 12 hours after the start of differentiation as an array of parallel filaments containing thickened regions suggestive of polyteny. Zybina and colleagues[18] [19] described non-classical polyteny in trophoblast polyploid cells as did Isakova and Mead[20] who reported that some nuclei are characterized by chromatin threads of different thickness which lie parallel to one another and frequently look "beaded," approximating the vision of chromatin fibers shown in Figure7(a).An even rarer sight can be seen in the damaged predome in Figure7(b).…”

“…A mass of chromatin is "whittled" down over time by "somatic ploidy divisions" to nuclei that will subsequently form a single-celled epithelial membrane. Data relevant to such a process in giant trophoblasts published more than 50 years ago and in more recent papers from the Zybina laboratory[18] [19] recognizing that polyteny was part of the life cycle of trophoblasts, described the process in this way, "The final step of the trophoblast giant cell differentiation is characterized by a transition from polyteny to polyploidy, with subsequent fragmentation of the highly polyploid nucleus into fragments of low ploidy." In essence, this is what we observe in the last 3 to 4 hours of dome formation.…”