Unusual characteristics of opaque Ishikawa endometrial cells include the envelopment of chromosomes with material containing endogenous biotin in the latter stages of cytokinesis

We have identified a small dynamic population of opaque cells in Ishikawa endometrial cultures whose unusual characteristics include the fact that chromosomes become enveloped during the final stages of cytokinesis by material staining for endogenous biotin. Endogenous biotin, ultimately shown to be due to mitochondrial carboxylases, was detected in a membrane that wraps around aggregated nuclei in syncytia that develop as part of the differentiation of domes in Ishikawa cells. (Fleming H et al. 1998). The “wrapped chromosomes” in individual opaque Ishikawa cells stain similarly suggesting a similar origin. We were able to show that opaque cells form from transparent monolayer cells, can be polyploid, and often appear to be detaching from the colony and from the underlying substrate. We were also able to show an opaque cell fissioning asymmetrically, to give rise to a monolayer cell whose nucleus appeared to be wrapped. We believe that the cycle of differentiation of monolayer cells into opaque, polyploid cells and depolyploidization back into monolayer cells is involved in the spatial extension of cells as they develop from discrete colonies into a confluent monolayer. Wrapping of chromosomes may ensure that complete genomes are inherited by daughter cells during depolyploidization.