Chromatin is highly dispersed in pluripotent cell nuclei of E3.5 blastocysts, but more compact in lineage-committed cells.

<p>Left panels show fluorescence microscopy of physical sections (70 nm thickness) of E3.5 blastocysts immuno-labelled for Nanog (A, epiblast), Gata6 (B, primitive endoderm) and Cdx2 (C, polar and mural trophectoderm). Although auto-fluorescence was detected in the nucleolus of some cells, this does not impact the ability to distinguish between nuclei that are positive or negative for Cdx2/Gata6. Positive cells are indicated by arrows in each image. Panels in the second column show low magnification mass-sensitive image of a positive cell. Merged phosphorus and nitrogen maps of the area indicated in the mass-sensitive images are shown at two magnifications in the right-side panels. 10 nm chromatin fibres are prevalent in epiblast (arrows) whereas blocks of compact chromatin (arrowheads) with fewer dispersed 10 nm fibres are observed in extra-embryonic progenitor cells. (D), Fluorescence images of DAPI stained nuclei of epiblast (left) and trophoblast (right) cells of a E3.5 blastocyst (scale bar represents 5 µm). (E), Chromatin compaction was quantified by measuring the distribution of chromatin cluster size in each cell type (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0010531#s4" target="_blank">materials and methods</a>for details). PE and polar TE cells contain larger chromatin clusters than EPI cells, suggesting that lineage-restricted cells have a more condensed chromatin architecture than pluripotent cells.