Cell junctions in explanted tissues from early chick embryos

Regional variations in the tightness of the ectodermal epithelium in the developing chick embryo: a study using ion-sensitive microelectrodes

In 2-day-old avian embryos there is a rosto-caudal gradient of interstitial pH (Gillespie and McHanwell: Cell Tissue Res., 247:445-451, '87). Neither the developmental significance nor the basic cellular mechanisms underlying this phenomenon has been studied. The present paper provides information about the interstitial potassium and calcium ion concentrations and the movement of these ions across the ectodermal epithelium. The data suggests a possible explanation for the longitudinal pH gradient in the embryo. The concentrations of potassium and calcium ions in the interstitial spaces were measured with ion-sensitive and conventional microelectrodes. In embryos bathed in solution containing 1 mM potassium, the potassium concentration in the region of the mesencephalon was 5.1 +/- 0.7 mM while in the region of the unsegmented mesoderm it was significantly lower at 3.3 +/- 0.4 mM (mean +/- S.E., n = 16). If embryos are exposed to extra-embryonic solutions containing 30 mM potassium, the K+ concentration in the mesencephalon is 13.0 +/- 0.8 mM and higher at 15.4 +/- 1.2 mM in the unsegmented mesoderm (n = 12). In embryos bathed in solutions containing 0.1 mM calcium, the interstitial calcium was found to be 1.1 +/- 0.52 mM in the mesencephalon and 0.42 +/- 0.19 mM in the unsegmented mesoderm (n = 3). In comparison, embryos bathed in solution containing 10 mM calcium had 1.9 +/- 0.2 mM rostrally compared to 3.71 +/- 0.63 mM caudally (n = 10). Thus it is possible to generate intra-embryonic ion gradients dependent upon the extra-embryonic ion concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential distribution of cell protrusions on the ventral surface of the deep layer in gastrulating quail and chick embryos

The ventral surface of the deep layer of gastrulating quail and chick embryos was examined using scanning electron microscopy. On the basis of cell protrusions, three or four different cell types were recognized. Cells covered with microplicae were found in the caudal region of the germ and as a narrow band extending along the lateral and anterior borders of the area pellucida. Cells covered with microvilli were found in a horseshoe-shaped zone in the anterior part of the germ. Beneath the rostral end of the primitive streak, the flattened deep-layer cells exhibited intercellular ridges and few microvilli. This area was surrounded by cells that usually had extended microvilli. The pattern of these cell types is discussed in relation to the formation of the different tissues that compose the deep layer in gastrulating embryos.

The primitive streak

The emphasis of this review is on the primitive streak of the chick embryo, collated with such information as is available on the mouse embryo. Little modern work has been published on any reptile primitive streak. The following topics are considered: evolutionary significance; formation of the primitive streak; ingression and de-epithelialisation; the basal lamina; migration from the primitive streak of the endoderm and mesoderm; the role of the extracellular matrix; changes in cell adhesiveness; regression of the primitive streak and its role in body patterning; the primitive streak and induction.

Intercellular junctions in human tooth-pulp cells in culture in vitro revealed by freeze-fracture, lanthanum impregnation and filipin treatment

Three kinds of intercellular junctions were detected between human dental pulp cells in explant culture with electron microscopy included filipin detection for cholesterol; desmosome-like junctions observed on ultrathin sections probably contribute to the cohesiveness between cells in culture. Gap junctions, responsible for intercellular communication, exhibited two morphologies on freeze-fracture replicas: a conventional arrangement of their intramembranous particles and a crystalline array corresponding to the formation stage of junctions. Primitive tight junctions were detected on freeze-fracture replicas but not on ultrathin sections. It is likely that they contribute to the cell-to-cell adhesion under culture conditions.

Design and application of a freeze-fracture stage with a cleaver device for Balzers 'freeze-etching' apparatus

A fracturing mechanism in the form of a double-wedged cleaver, used previously on other freeze-fracture machines, has been incorporated in the Balzers BAF 400 D apparatus. The design of the stage, with the cleaver, is explained and its performance and advantages are outlined. By minimizing mechanical damage to the exposed surface of the frozen specimen and reducing contamination by effective shrouding, an improvement in the quality of the replicas is achieved. The suitability of this mechanism for the fracturing of tough tissues such as skin is also outlined.

Interaction of three human malignant cell lines with chick hypoblast in culture

The hypoblast (lower layer) was dissected from young chick blastoderms and explanted in vitro, where it formed an epitheloid sheet. Cells from the following malignant lines were explanted on top of the sheet both as aggregates and as cell suspensions: Hu456 human bladder carcinoma, SAOS-2 human osteosarcoma, LICR(LOND)-HN-4 laryngeal carcinoma. The interaction of the malignant cells with the hypoblast was studied by time lapse cinephotography, light microscopy, and transmission electron microscopy. All malignant cells penetrated through the hypoblast, so that a gradually enlarging hole formed in it. Apart from this common pattern of behaviour, the three types of malignant cells differed in their interactions with the hypoblast in the following ways. 1) Both the Hu456 and to a lesser extent the SAOS-2 cells brought about an initial retraction of the hypoblast so that a temporary cell-free space was formed. No such retraction occurred in response to the LICR-(LOND)-HN-4 cells. 2) Each of the three types of malignant cells migrated for some distance beneath the hypoblast, and in this area of underlap, there were differences in the amount and disposition of extracellular material. Thus, there was more extracellular material between the hypoblast and underlying SAOS-2 cells than between the hypoblast and underlying Hu456 cells, whilst there was no extracellular material between the hypoblast and underlying LICR(LOND)-HN-4 cells. Indeed, the hypoblast and LICR(LOND)-HN-4 cells often shared desmosomes. 3) When explanted as aggregates on hypoblast Hu456 and SAOS-2 cells left the corona and migrated as solitary cells underneath the hypoblast in contrast with control aggregates explanted on plastic. These cells which had migrated beneath the hypoblast were flatter than their corresponding control cells which had spread on the plastic substrate. The flatter cells appeared to have been using the extracellular materials as a substrate, rather than the plastic. Such differences in the migratory behaviour between experimental and control cultures were not observed with LICR(LOND)-HN-4 cells.