Reorganization of the apical cytoskeleton of uterine epithelial cells during early pregnancy in the rat: a study with myosin subfragment 1

Abstract

Actin filaments were identified in the epithelial cells of rat uterus following detergent extraction and decoration of microfilaments (MF) with myosin subfragment 1 (S1). MF connections with cytoplasmic organelles and the apical plasma membrane are also described. Transmission electron microscopy revealed that the regular microvilli of non-pregnant, oestrous animals contain several decorated MF with rootlets descending into a densely filamentous terminal web. Following mating, the actin cytoskeleton was examined on days 1, 3 and 6 of pregnancy. In this period, the irregular projections that replace MV assumed an underlying, dense network of decorated MF, whilst smoother surfaces displayed few cytoplasmic filaments. At the time of blastocyst implantation, a structured terminal web was no longer present. Structural details were revealed concerning the contents of large, bleb-like projections found on the apical surface.

Uterine receptivity and the plasma membrane transformation

“…Desmosomes (d) are considerably reduced along the lateral plasma membrane at this time and the terminal web is completely lost. membrane of uterine epithelial cells and these changes occupy most of early pregnancy in the rat and mouse with long, regular microvilli being converted into short, irregular structures as early as d 3-2 ~3 d before the blastocyst even enters the uterus [7,[89][90]. As we have also seen, in a wide diversity of species, there are changes in the apical plasma membrane which have features in common with those seen in rats and mice and in many of these other species, closure of the uterine lumen does not occur.…”

“…They found that in either case, blastocysts were only able to begin implantation when the apical membrane flattening was present. Since this appearance is found in uterine epithelial cells during pseudopregnancy in both mice [8] and rats [9] and can also be induced in virgin ovariectomized rats treated with ovarian hormones in the absence of blastocysts [2,7,11], it must be a maternal response not requiring a blastocyst for its occurrence. This view is further strengthened by the observation that the apical plasma membrane undergoes the same sequence of changes (although perhaps according to a slightly different schedule) whether it is opposed to a blastocyst or to uterine epithelial cells from the other side of the uterus [2, 4, 5, 7-9, 13, 14].…”

“…Under the influence of either hormone alone, change in the apical plasma membrane is mostly limited to alterations in the height and frequency of microvilli [1,2,3 for review]. However, during early pregnancy when progesterone and oestrogen act together in the peri-implantation period leading to uterine receptivity for implantation of the blastocyst, the apical plasma membrane of uterine epithelial cells undergoes a more marked form of structural change during which over the several days of early pregnancy, and beginning as early as d 2 of pregnancy, it gradually loses regular microvilli and becomes very flat [2,[4][5][6][7]. Indeed, the membranes of uterine epithelial and trophoblast cells in the implantation chamber come to run more or less parallel all along the area of contact as more generally do the membranes of opposing uterine epithelial cells outside the implantation chamber especially in species with uterine closure [8,9].…”

Endometrial receptivity to embryo implantation: molecular cues from functional genomics

“…In addition, the long and abundant epithelial microvilli retract, creating multiple flat areas in the surface (Schlafke & Enders, 1975;Murphy, 1993). This process could be related to the destabilization of the actin cytoskeletal network observed in these structures (Luxford & Murphy, 1989;Luxford & Murphy, 1992). On the other hand during the receptivity period it has been reported biosynthesis and expression of a different repertoire of surface proteins in the apical (Aplin, 1997;Lessey, 1998;Kirn-Safran & Carson, 1999) and basal-lateral domains (Rogers & Murphy, 1992;Albers et al, 1995;Murphy, 1995;Nikas, 1999).…”

Transmission electron microscopy of marine crustacean eggs

“…Secondary treatment with osmium tetroxide over a period of no more than 2.5 hours is standard for fixation of lipids (Høeg et al, 2004) and this stage may be combined with the primary fixative (Hayat, 1981). There are several embedding media available for TEM ("TAAB": Luxford & Murphy, 1992; "Epon-Araldite": Sloane et al, 1994;"Spurrs": Menzies & Kourteva, 1998;and "LR White": Radford & White, 1998) that differ in their ability to penetrate the specimen and in their hardness; infiltration times of 24 hours are usual for these resins (Paffenhöfer & Loyd, 2000).…”