Video observations on human blastocyst hatching.
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Blastocyst↗
Biomedical subjects
Henry Sathananthan
Publications and source records attributed to Henry Sathananthan.
Critical evaluation of human blastocysts for assisted reproduction techniques and embryonic stem cell biotechnology.
Critical examination of 30 blastocysts by transmission electron microscopy (TEM) reveals cellular features not usually evident, including abnormalities of cell structure and aberrations such as multinucleation, internal fragmentation, phagocytic or degenerating cells. Invariably, such blastocysts are inactive and delay or fail to expand and hatch in vitro. Hatching seems to be a major problem in ageing blastocysts due to inactivity of the surface epithelium of trophoblast cells that do not stretch and expand. These lack surface microvilli and contractile tonofilaments that anchor on to specialized cell junctions such as desmosomes. Trophoblast expansion and consequent thinning of the zona is a prerequisite to proper hatching aided by the hydrostatic pressure in the blastocoele and by specialized cells at hatching points. Proper assessment of the inner cell mass is required if a healthy population of cells is to be harvested for embryonic stem cell culture. An inactive blastocyst is obviously not good material and could have a defective inner cell mass (ICM). Normally approximately 3-5% of cells are mitotic in blastocysts and arrested cell division is also an indicator of inactivity. An attempt has been made to evaluate blastocyst internal structure for both assisted reproduction techniques and embryonic stem cell biotechnology.
Biotechnology↗
Mechanics of human blastocyst hatching in vitro.
Critical examination of 30 blastocysts by transmission electron microscopy at various stages of blastulation and hatching, has revealed the presence of specialized, plump, trophoblastic cells at the points of hatching, which seem to aid in initial breaking of the zona pellucida (ZP) and then widen its opening to permit the progressive emergence of the embryo in amoeboid fashion, when it acquires a characteristic dumb-bell shape. These cells are named 'zona-breaker' cells and their characteristics are described. Normally, trophoblast cells in expanding blastocysts are flattened (squamous), forming a continuous robust epithelium with specialized cell junctions. Bundles of tonofilaments anchor onto desmosomes, forming a terminal web. Proper expansion of blastocysts by intake of fluid into the blastocoele causes an increase in internal hydrostatic pressure that stretches the trophoblast epithelium leading to an enlargement of its volume two- to three-fold, consequently thinning the zona prior to hatching. This is an important prerequisite to normal hatching. The blastocysts usually hatch out at the pole opposite the inner cell mass (ICM), though a few hatch out at the embryonal pole or elsewhere. In all cases zona-breakers seem to play a vital role in the hatching process.
Blastocyst↗
The fine structure of human embryonic stem cells.
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.
Blastocyst↗