Elektronenmikroskopische Untersuchungen �ber die Blastozyste des Kaninchens vor der Implantation in bezug auf ihre Wechselbeziehung zur uterinen Umgebung

Uteroglobin in the developing rabbit conceptus in vivo and in vitro

Uteroglobin (UGL) was measured in day-4 to day-10 rabbit conceptuses by a competitive ELISA. Levels in blastocyst fluid, tissues, coverings and in the early fetus were determined separately. The total amount of UGL increased from 18.4 ng to 6.8 micrograms per conceptus. The UGL content of individual day-6 blastocysts was studied in vitro. Culturing was carried out up to 60 h in Ham's F10 medium with polyvinylpyrrolidone as macromolecular component, with and without progesterone, and with progesterone plus estradiol. UGL was determined in the blastocyst fluids, tissues with coverings and in the culture media. After labelling with [35S]-methionine, protein patterns of total blastocysts and of culture media were analysed by two-dimensional gel electrophoresis and fluorography. The morphology of cultured blastocysts was examined by electron microscopy. During 60 h of culture, the blastocysts expanded in diameter by 84%, and released 19% of their initial UGL content into the medium, independent of the hormonal substitution. Neither de novo synthesis, nor degradation of UGL was found: the protein remained unlabelled in fluorography, and its total quantity was not significantly different from that of non-cultured controls. Trophoblast, endoderm and embryoblast cells showed well preserved cell organelles and intercellular junctions, while the morphological differentiation of the germ layer was inhibited.

Uptake and accumulation of tritiated uteroglobin by day-6 rabbit blastocysts

Uptake of uteroglobin (UGL) by day-6 rabbit blastocysts and the intracellular fate of this protein were studied by light- and electron-microscopic autoradiography, immunocytochemistry and acid-phosphatase cytochemistry. UGL, labelled with N-succinimidyl-(2-3-3H)-propionate, was administered to embryos in vitro for 25 min to 4 h. The kinetics, determined from light-microscopic autoradiographs, showed a continuous uptake of the labeled protein over a 4-h period of incubation. At the ultrastructural level, increasing numbers of silver grains and an intense UGL immunoreaction in protein vacuoles and crystalloid bodies of trophoblast cells indicated that 3H-UGL had accumulated in these organelles. The presence of crystalloid inclusions in protein vacuoles suggests their origin by a condensation of the protein content, including UGL. Lysosomes containing radioactivity were rarely found, suggesting a very low degradation rate of the 3H-UGL. Protein vacuoles and crystalloid bodies exhibited no acid phosphatase reaction. The enzyme was mainly found outside the basal and lateral cell membranes of trophoblast cells, and on the rough endoplasmic reticulum of endoderm cells.

Polar trophoblast (Rauber's layer) of the rabbit blastocyst

The germinal area of the rabbit blastocyst between 108 h postcoitum (pc) and 168 h pc has been examined by scanning electron and transmission electron microscopy. At 108 h and 120 h pc the polar trophoblast (Rauber's layer) is an intact epithelium overlying the epiblast of the inner cell mass. By 132 h pc the polar trophoblast cells begin to separate at multiple foci, exposing the underlying epiblast. Most of the polar trophoblast cells have become individually separated at 144 h pc. The villous, electron-dense polar trophoblast cells can be easily distinguished from the cells of the epiblast, which have smooth apical surfaces. By 162 h pc the polar trophoblast cells have disappeared from the germinal area. Before the polar trophoblast breaks up, the underlying epiblast cells are only loosely attached to one another. Concurrent with the disintegration of the trophoblast epithelium, the epiblast cells change in shape so that their lateral borders become closely apposed, and junctions develop to form a new epithelium. The epiblast becomes contiguous with the mural trophoblast, and thus the blastocyst does not lose its turgidity as the permeability seal is maintained. There are two classical theories on the fate of the polar trophoblast: the cells die, or they become incorporated into the epiblast as living cells. In newly exposed epiblast the presence of very large phagosomes, which are not found when the polar trophoblast is still intact, favors the first hypothesis and indicates that in the rabbit the epiblast is involved in the phagocytosis of the polar trophoblast.

Development of preimplantation rabbit embryos after in-vitro culture and embryo transfer: an electron microscopic study

Compared to in vivo development, in vitro culture of mammalian embryos results in developmental retardation. To study the potential of reversibility of growth retardation we investigated ultrastructurally day 3 rabbit embryos after 1 day in vitro, and cultured embryos that were transferred after culture into recipient rabbits for 1 day. Morphology was compared with ultrastructure of noncultured controls. The noncultured embryos were compacted morulae; the characteristic ultrastructure is described in detail. After 1 day in culture, morulae had developed into early blastocysts. However, unlike the results in vivo, expansion of the blastocysts did not occur and some of the cultured embryos developed trophoblast herniations. In all cultured embryos morphological signs of degeneration were seen with swollen mitochondria, with a dense, granular appearance of the cytoplasm, and with an increase in number of lysosomes. Transfer of cultured blastocysts into uteri of day 3 pseudopregnant recipients resulted in ultrastructurally intact and expanded blastocysts. Transfer into uteri of day 4 pseudopregnant recipients and into uteri of nonpregnant recipients, however, did not yield reversibility of the unphysiological features suffered during the previous time in culture. Although blastocysts were well expanded, distinct signs of injury to the blastomeres were present, proceeding from loss of complete blastomeres to structural changes such as large lamellar structures, dilation of smooth endoplasmic reticulum and Golgi complexes, and clumping of mitochondria. We conclude that developmental retardation during in vitro culture is accompanied by distinct morphological changes. As soon as 24 hr after transfer, these changes can be reversed. This compensation, however, is achieved only if embryos are transferred into recipients that are adapted to the embryo's developmental stage, which is not identical to the embryo's chronological age. Our findings demonstrate that the period of 24 hr of in vitro development matches only a few hours of in vivo development.

The ultrastructure of preimplantation hamster blastocysts developed in vivo and in vitro

Scanning electron microscopy of zona-free blastocysts showed bulging trophoblast cells possessing slender microvilli and many small projections of various lengths. The trophoblast cells contained mitochondria in two shapes. One type consisted of spheroids with a few mitochondrial inner membranes. The other type had a more conventional appearance. Fibrous material varied in amount. The trophoblast cells from blastocysts cultured for 1 day had an appearance similar to that of trophoblast tissue fixed in vivo. However, the large, dense mitochondria with few cristae had diminished in number, and globular mitochondria occurred more frequently. Furthermore, the fibrous material was more sparsely distributed after culture. The experiments demonstrated that cultured hamster blastocysts have ultrastructural characteristics similar to those of in vivo blastocysts. Experiments are in progress to test whether the in vitro technique can determine the growth requirements of the hamster blastocyst.