Extraembryonic Epithelium Research Articles

Promotion of osteogenesis by extra-embryonic epithelia in maxillary mesenchyme of the embryonic chick

Maxillary mesenchyme (HH stages 19–21), separated from its epithelium and grown as a graft on the chorioallantoic membranes of host chick embryos, did not form membrane bone. However, when isolated maxillary mesenchyme was recombined directly with chorioallantoic endoderm or chorioallantoic ectoderm and then grafted, it did form membrane bone in 87.5 and 70% of cases, respectively. This novel finding of extra-embryonic epithelia eliciting an osteogenic response from membrane bone-forming mesenchyme indicates that the germ-layer origin of an epithelium does not necessarily restrict its potential to promote membrane bone formation.

Histocompatibility antigens, transferrin receptors and extra-embryonic markers of human amniotic epithelial cells in vitro

This study has shown that fresh amniotic epithelial cells which are negative by indirect immunofluorescence for HLA and Trf receptors become positive for both of these markers following prolonged culture. In addition, the amniotic antigens which are characteristic of fresh amniotic epithelial cells are lost and replaced by trophoblast antigens subsequent to maintenance of the cells in vitro. These observations suggest that, although the expression of HLA and Trf receptors are apparently negative in vivo, such gene products become activated and manifest in plasma membranes following exposure of the cells to culture conditions. In addition, the normal manifestation of the amnion antigens is lost following prolonged periods of culture. These findings indicate that the coding and expression of normally accepted transplantation antigens undergo a significant perturbation in vitro, and that markers of normal extra-embryonic epithelium in vivo are lost after the cells have been cultured in vitro.

Involution des annexes embryonnaires dans l'oeuf de Locusta migratoria migratorioides R. et F. (Orthoptera : Acrididae) : Analyse cytologique

The resorption processes of the extra-embryonic epithelia in the egg of the African migratory locust, Locusta migratoria migratorioïdes R. and F., have been analyzed at the cellular level, more particularly for the gigantic serosal cells. While definitive dorsal closure is taking place, those flattened epithelia retract and become cuboidal. Then their cells show typical alterations : cytoplasmic and nuclear volumes change; cytoplasmic components segregate; vaculoes, lipidic inclusions and glycogen granules appear in the cytoplasm; chromatin becomes pycnotic and gains a RNase-resistant affinity for pyronin. The process of dissociation of extra-embryonic membranes varies according to the nature of the epithelium considered, and to its position in relation to the embryo. Once they have been incorporated, the cells degenerate through autolysis. Most of them are phagocytized (heterolysis) either by hemocytes (post-oral amnion) or by vitellophages in the dorsal complex of resorption (serosa). At first, the post-mortem changes in serosal cells begin with the intense condensation of cytoplasmic ribonucleoproteins and the swelling of mitochondria; then comes the lysis of those cytoplasmic components, of the nuclear membrane and of the pycnotic chromatin. In the cytoplasm of vitellophagocytes, residual bodies are still visible 24 hr before hatching. The movements of the vitellophages have been followed: in the anterior part of the yolk, they perform a centripetal migration towards the serosal cells which have been incorporated. Later they move towards the periphery, and so could play a part in the formation of the definitive midgut epithelium.