Histology and fine structure of the avascular and vascular yolk-sac placentae and the obplacental giant cells in the rabbit

Chorionic gonadotropin-like proteins in the obplacental giant cells of the rabbit

Obplacental giant cells are enlarged cells, found following implantation, in the antimesometrial region of the rabbit uterus. They probably originate from trophoblastic knobs that traverse the uterine epithelium during early implantation. Little is known about their function. In this study, trophoblast, placental, paraplacental and obplacental tissues at days 7-15 post-coitum, and enzyme-isolated giant cells at day 15 were studied by two-dimensional gel electrophoresis, followed by immunoblotting and light-microscopic immunohistochemistry, for the presence of human chorionic gonadotropin-like proteins. Immunostaining was performed by using anti-human chorionic gonadotropin antibodies. In gel electrophoresis of obplacental tissue and isolated giant cells, two proteins of human chorionic gonadotropin-like antigenicity at 26 kDa with pIs equivalent to pH 6.4 and 6.6 were found; they were absent in the placenta, paraplacenta, day-7 blastocyst and day-8 trophoblast. The onset of synthesis of these proteins could be observed when day-8 trophoblastic tissue was cultured in vitro for 24 h. In immunohistochemistry, only the obplacental giant cells showed a positive reaction, indicating that the production of chorionic gonadotropin occurs in this cell type.

Giant and binucleate trophoblast cells of mammals

The cellular origin, structure, and function of trophoblastic giant cells (GC) and binucleate cells (BNC) are reviewed. Mammals in which these cells have received the greatest attention include rodents, rabbits, and humans (GCs), and ruminants and equids (BNCs). In almost all cases these cells arise from the cytotrophoblast. All are large cells and contain either two diploid nuclei (BNCs), multiple nuclei (human placental bed GCs), or single nuclei with amplified DNA content (rodent and rabbit GCs). Giant and binucleate cells typically exhibit the capacity for migration or invasion, although the degree of migratory activity varies between species. While most end up within, or at the interface with, endometrial tissue, in some instances the GCs or BNCs contribute directly to the interhemal membrane of the placenta. Hormone production is a property which most GC-BNC populations have in common. Lactogen or gonadotropin has been documented in almost all cells of this type examined to date, and in some animals they are also steroidogenic (e.g., rats and sheep). In spite of some common features, both structural and functional differences remain and it is suggested that use of terms such as mononuclear giant cells, multinucleate giant cells, and binucleate cells be continued rather than assuming that these cells are all members of a single trophoblastic subtype.

Obplacental giant cells of the domestic rabbit: development, morphology, and intermediate filament composition

Obplacental giant cells are large (less than or equal to 210 microns) polyploid cells that appear in the stroma of the pregnant uterus of the rabbit following ovoimplantation. Histological examination of a complete developmental series indicates that obplacental giant cells arise from trophoblastic knobs that have traversed the uterine epithelium during early implantation. During maturation, the cells undergo a massive (approximately 6,000%) increase in volume and penetrate deeply into the uterine stroma and myometrium, where they often become associated with blood vessels and smooth muscle cells. Giant cells at mid-gestation contain one or two large nuclei with prominent nucleoli and appear to be amitotic. They are rich in Golgi complexes, RER, SER, and cortically distributed cytoplasmic filaments, and contain intracellular canaliculi lined by microvilli. Giant cells vary with respect to the occurrence of lipid droplets, phagocytotic inclusions, lysosomal structures, and electron-dense granules. Immunocytochemistry demonstrates that the giant cells exhibit intermediate filaments related to cytokeratin and vimentin, but are negative for desmin and for an endothelial cell marker, Factor VIII-related antigen. The cells are positive for cytokeratin from their inception, but only become vimentin-positive between Days 12 and 15 of pregnancy, a change seemingly related to their detachment from epithelial tissue to take on an independent existence. Our findings indicate that the giant cells originate from obplacental trophoblast and, at maturity, exhibit cytoskeletal characteristics of isolated epithelial cells, as well as a complement of organelles suggestive of synthetic activity.

Erythropoiesis in the yolk sac of the bat Tadarida brasiliensis cynocephala

The process of erythropoiesis and vasculogenesis in the yolk sac of the bat (Tadarida brasiliensis cynocephala) has been studied through the use of both light and electron microscopy. Stem cells arise from the leading edge of the migrating splanchnic mesoderm and transform into primitive erythroblasts. Differentiation involves either contact or association with the endodermal cells, since all erythropoietic activity occurs on the endodermal side of the expanding vascular bed, and many of the cells are in close apposition to the lateral or basal plasma membranes of the endodermal cells. Endodermal cells also phagocytize developing primitive erythroblasts during the later stage of the process when erythropoiesis is subsiding in the yolk sac. Cells destined to become the endothelium of the expanding vascular bed also arise from the leading edge of the migrating splanchnic mesoderm. Their process of differentiation involves the development of cytoplasmic extensions that may surround a group of differentiating erythroblasts, enclosing them in the newly formed lumen of the blood vessel. The cytoplasmic extensions make contact and develop junctional complexes with similar processes from other cells to complete the lumen of the lengthening vascular bed. Cells of the granulocyte series or megakaryocytes are not observed in the yolk sac of the bat as has been described in certain other species.

The human yolk sac and yolk sac carcinoma. An ultrastructural study

The ultrastructure of the yolk sac of a 39 day old human embryo was studied. The subcellular organization was suggestive of a highly specialized absorptive function proceeding in an exocelomic-viteline direction. These findings, compatible with intense metabolic activity, are at variance with the concept of rapid involution of the yolk sac following completion of its hemopoietic and angiogenetic functions. The speculation is advanced that a potential avenue exists in the yolk sac whereby maternally derived products encounter fetal endoderm. Ultrastructural features in the normal yolk sac were compared to those existing in a tumor showing the "endodermal sinus" pattern, and reviewed in the light of the pertinent literature. These findings support the concept that attributes an endomesoblastic derivation to such neoplasms.

Morphological changes in the trophoblast, uterus and corpus luteum during delayed implantation and implantation in the western spotted skunk

Morphological interactions of tropholbast and uterus from stages of preimplantation and implantation were studied in 14 western spotted skunks. In addition, the granulosa lutein cells and plasma progesterone levels were studied. In animals several days from implantation the height of epithelial cells decreased, but began to increase in animals approaching implantation. During the preimplantation period a few leucocytes infiltrated the epithelium, but in animals just prior to implantation many leucocytes infiltrated the epithelium.