The fine structure of human embryonic stem cells

Abstract

The fine structure of human embryonic stem (ES) cell colonies was analysed by transmission electron microscopy (TEM) after 35 passages of in-vitro culture. Most cells formed compact, saucer-shaped colonies with epithelioid cells on the periphery and polygonal cells within the colony. Three morphological types of cells were identified based on their fine structure: undifferentiated cells resembling inner cell mass (ICM) cells of blastocysts; protein-synthesizing cells at the onset of cellular differentiation; and compact masses of secretory cells resembling unicellular goblet cells of the intestine. The predominant cell type was the undifferentiated ES cells resembling ICM cells of blastocysts. These cells had large nuclei containing reticulated nucleoli, well-developed rough endoplasmic reticulum (RER), Golgi complexes, elongated tubular mitochondria, lysosomes and typical centrosomes with centrioles associated with microtubules and microfilaments, organizing the cytoskeleton. Some ES cells have very large nuclei and scanty cytoplasms with fewer organelles. The isolated or attached protein-synthesizing cells at the onset of differentiation had extensive RER and large Golgi complexes. The morphologically differentiated cells formed compact colonies and resembled goblet-like cells in microstructure. They had RER and large Golgi complexes associated with secretory vesicles. The epithelioid cells at the periphery were columnar and largely polarized by centrosomes associated with Golgi complexes. Epithelioid cells in all three categories had specialized cell junctions (desmosomes), anchored by tonofilaments, and surface blebs. Isolated cells were seen on the surface, towards the centre of the colony, and their free surfaces had microvilli and larger blebs. Approximately 3-5% of all cells were mitotic, with typical bipolar spindles organized by centrosomes, pivotally located at the poles, and appeared to resemble typical somatic cells.

The Senescence-Related Mitochondrial/Oxidative Stress Pathway is Repressed in Human Induced Pluripotent Stem Cells

“…3C). A similar MTG pattern has been described in undifferentiated hESCs and explained by the fact that cells at the colony periphery might show specific epitheliod appearance and may be on the verge of differentiation [8,20]. Upon differentiation into DF cells, MTG labeling revealed mitochondria exhibiting a dense tubular network rather than a scattered-dot pattern as in the parental cells (Fig.…”

“…Finally, we observed that mitochondria within iPS and ES cells were assuming a bipolar clustering at the two sides of the nuclei (Fig. 4C, arrows), a typical intracellular distribution previously described in mouse and human ESCs [20][21][22].…”

“…Structural analyses of mitochondria within hESCs have demonstrated an immature network characterized by few organelles with poorly developed cristae with peri-nuclear polarization [20][21][22]. Studies of organelle number and functionality confirmed a low content of mitochondrial DNA (mtDNA) and low levels of intracellular ATP and ROS [7,8,23].…”

Feeder-Free Monolayer Cultures of Human Embryonic Stem Cells Express an Epithelial Plasma Membrane Protein Profile

“…After nine passages (3 weeks) under feeder-free conditions, these cells collectively retained expression of sox2 in addition to components of epithelium-associated cell-cell adhesion complexes. They thus resemble the central top layer of hESC colonies cultured on feeder cells [9,16].…”

“…hESCs on feeder cells have been described as multilayered colonies with, on their periphery, epithelium-like polarized cells that are connected by desmosomes [9]. In addition to ESC-associated transcription factors, such as oct4, sox2, and nanog, epithelial proteins have been reported to be expressed by hESCs on feeder cells [10 -14].…”