Blastocyst attachment and morphogenesis of ectoplacental cone in mouse.
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Date
1984-07
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Abstract
Mouse blastocyst attaches on the antimesometrial side of the uterus through mural
trophoblasts. Later the polar trophoblasts begin proliferation, and rapid multiplication
towards the mesometrial side of the uterus occurs resulting in the formation of an excrescence
designated as ectoplacental cone. The morphogenesis of ectoplacental cone, viewed in utero,
initiates on day 6 post-coitum when microvilli of the trophoblast and the uterine epithelial cells
are lost and as a result of this opposing membranes appear interlocked with each other. Soon
following the invasion by surrounding trophoblasts the necrosis of the epithelial cells starts.
Mitochondriae of the epithelial cells, at this stage, are shrunken and lack well defined cristae.
Several leucocytes are seen at the site and few electron dense structures appear wedged between
the trophoblasts and epithelial cells. At places the cell membrane is studded with the basement
membrane of the uterine epithelium giving an impression of a bristle coated membrane. By day
7 post-coitum the basement membrane has almost disappeared leaving trophoblast cells to
develop close contact with stromal cells. Collagen fibres appeared between the trophoblasts
and the stromal cells, many large inclusions of high electron density representing engulfed
necrotic epithelial cells are discernible. On day 8 post-coitum the ectoplacental cone is fully
developed. Four types of trophoblast cells can be identified in it: (i) basal cells lying on the base
of the cone, are polyhedral and compactly arranged. They have a large nucleus and well
developed nucleoli, (ii) central cells forming the middle area of the cone are of two types; one
contained several osmiophilic granules enclosing translucent area (eccentric) and a well
developed golgi complex around the nucleus, while the other has many heterophagosomes,
vacuoles and residual bodies and (iii) peripheral cells contained several pleomorphic structures
resembling secondary lysosomes. Minute dense granules and band of microfibrils on the apical
region of these cells are seen. Dense granules probably release lytic proteins at the site and
microfibrils help in forming cytoplasmic projections.
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Keywords
Morphogenesis, ectoplacental cone, early mouse embryo
Citation
Mehrotra P K. Blastocyst attachment and morphogenesis of ectoplacental cone in mouse. Journal of Biosciences. 1984 July; 6(suppl_2): s43-s52.