Changes in number, mobility, and topographical distribution of lectin receptors during maturation of chick erythroid cells

The blocked pinocytic activity of mitotic cells is restored in mitotic-interphase hybrids

During mitosis there is an abrupt inhibition of a wide range of membrane functions, including fluid-phase and adsorptive pinocytosis. We have used cell hybrids formed between mitotic and interphase cells to approach the mechanism of this inhibition. We report that fluid pinocytosis is reactivated in the mitotic partner of hybrids formed between mitotic and interphase Chinese hamster ovary (CHO) cells. It thus appears that the interphase cell provides some necessary element(s) for membrane activity during mitosis. This dominance of interphase membrane properties stands in contrast with earlier evidence that mitotic nuclear properties dominate in similar mitotic-interphase hybrids.

Surface domains of the guinea pig sperm defined with monoclonal antibodies

Four monoclonal antibodies have been produced that recognize surface molecules of the guinea pig sperm. Each antibody binds to a unique, localized region of the sperm surface. The four antibody-binding patterns are restricted to the anterior head, of the sperm, the posterior head, the whole head and the posterior tail. Based on absorption experiments, the surface molecules detected by the antibodies are differentiation antigens. Three of the antibodies immunoprecipitate 125I-labeled protein antigens. The molecular weights of the polypeptides observed after SDS-PAGE are 52,000 (anterior head), 42,000 (whole head), and 60,000 (posterior head). The observed monoclonal antibody-binding patterns suggest that the guinea pig sperm surface is divided into a minimum of four domains.

Polar differences of delayed and implanting mouse blastocysts in binding of Alcian Blue and concanavalin A

Mouse blastocysts in delay of implantation and after an 18-hour activation for implantation by estrogen were recovered by flushing with glutaraldehyde containing Alcian Blue or by flushing with cold Dulbecco's PBS containing 0.1% sodium azide for further processing according to an Alcian Blue technique and a ConA-latex technique, respectively. Blastocysts in delay of implantation showed no or only faint staining with Alcian Blue, while blastocysts activated for 18 hours displayed a marked staining of the abembryonic pole. Binding of ConA-latex spheres demonstrated a markedly higher density at the abembryonic end of both delayed and implanting blastocysts. It is concluded that, as demonstrated by the Alcian Blue technique, the abembryonic trophoblast, which is the first one to attach and invade at implantation, has changed the properties of the extracellular coat, probably in a way that favors increase of adhesiveness and invasiveness. The similarity in pattern of ConA binding of both delayed and implanting blastocysts, however, suggests that this property is related more to preimplantational differences in proliferative activity of the two poles than to implantatory changes.

Lectin teratogenesis: defects produced by concanavalin A in fetal rabbits

Concanavalin A (con A) is teratogenic to rabbit embryos during gestational days 12--15. Intracoelomic injections of 40 microliter con A solution (4 microgram/microliter) were performed on rabbit embryos during gestational days 10--15. Control embryos received either 40 microliter of saline, sham injection or no treatment. Con A caused increased fetal resorptions on days 10 and 11, but malformation levels did not differ from controls. On days 12--15, con A produced craniofacial, trunk and limb anomalies. The highest percentage of malformation occurred on day 14. The defects were classified into four groups: (1) malformations of limbs including paw and digital dysplasias as well as fusions of the limbs to the head or body wall; (2) "closure" defects such as umbilical hernia, encephalocoele, exencephaly or ectopia cordis; (3) "contracture" defects such as club paws, extended knees, or clenched digits, which exhibited normal osseous and cartilaginous skeletons; and (4) miscellaneous, non-specific anomalies including fused or dysplastic sternebrae or ribs. Histologic analysis of selected 12-day embryos 4 to 18 hours post-injection was performed to ascertain potential sites of teratogenic action. At 12 hours ectodermal necrosis was observed in the limb buds adjacent to the apical ectodermal ridge. By 18 hours, the ectoderm had eroded, exposing the basal lamina to the amniotic fluid. Focal areas of mesenchymal necrosis were observed in association with the ectodermal erosion. The potential roles of amniocentesis and limb bud repair in the genesis of the malformations are discussed.

Molecular changes in the membranes of mouse erythroid cells accompanying differentiation

The development of the mouse erythroblast to a mature erythrocyte is accompanied by changes in the composition and properties of the plasma membranes of these cells. Using double fluorescence techniques, we have simultaneously determined the distribution of lectin receptors and spectrin on the membranes of these cells. The lateral mobility of the lectin receptors in the membranes decreases as differentiation proceeds, and this is accompanied by an increasing concentration of spectrin associated with the membranes. The most significant concentration of spectrin occurs, however, during the enucleation of the late erythroblast, where we observe a complete segregation of the spectrin to the incipient reticulocyte, as well as a previously observed enrichment of receptors for concanavalin A into the plasma membrane surrounding the extruding nucleus. On the basis of these and other observations, we explore the possible molecular mechanisms involved in erythroblast enucleation and the role of spectrin in the regulation of protein mobility in erythroid cell membranes.

Alteration of the enucleating erythroblast glycocalyx

Plasmalemmal differentiation of the enucleating normoblast of rabbit and rat was studied by means of cytochemical methods and freeze-etching. Staining with colloidal iron revealed about identical amounts of iron particles bound to various areas of the normoblast membrane. Cationized ferritin and ruthenium red, likewise, failed in the demonstration of significant changes of the enucleating normoblast glycocalyx. Despite these findings the topo-optical staining with toluidine blue showed the plasmalemmal envelope of the protruding normoblast nucleus moderately birefringent, clearly discriminated from the intense anisotropic staining of the future reticulocyte membrane. The ferritin-labeled snail lectin anti AHP localized a great number of binding sites at the plasmalemmal envelope of the nucleus under extrusion. That is in sharp contrast with rather low lectin binding to the future reticulocyte membrane which amounts to about 30 to 50% of the nuclear envelope label. The findings provide evidence of unmasking of bindings sites of the normoblast membrane. Apparently, the effect is due to conformational changes of the cell membrane, rather than it could be attributed to degradation of glycoproteins. Moreover, enucleation kinetics may also be related to supramolecular changes of membrane structure albeit missing evidence for the rearrangement of membrane particles.

Lateral mobility of human erythrocyte integral membrane proteins

Fluorescein isothiocyanate-labelled integral membrane proteins are mobile in the membranes of human erythrocytes that have fused (and haemolysed) by Sendai virus or polyethylene glycol. Minimum diffusion coefficients are of the order of 10(-11) cm2 s-1 at 37 degrees C. This mobility is reduced several-fold at room temperature, not detected at 0 degrees C, and is significantly greater in fresh than in aged blood. Mobility was assessed by observing the spread of fluorescence on labelled cells which had been fused with unlabelled cells; neither intramembrane particle aggregation nor spectrin release occurred during this process.

Clustering and endocytosis of membrane receptors can be induced in mature erythrocytes of neonatal but not adult humans

Concanavalin A (Con A) is taken up by endocytosis in mature erythrocytes of newborn humans but not in adult red cells. Thin sections of neonatal cells incubated with ferritin-conjugated Con A at 37 degrees show ferritin clusters on invaginations at the surface and in intracellular vesicles, but such invaginations and vesicles are absent with adult cells. The endocytosis induced by ferritin-conjugated Con A is inhibited at 0 degrees, and by methyl-alpha-D-mannopyranoside at 37 degrees. Succinylation of Con A, which is known to convert it from the tetrameric to dimeric form, renders Con A inactive in cell agglutination and endocytotic vesicle formation, presumably by reducing the number of oligosaccharide chains simultaneously bound by a single Con A molecule. Ferritin-conjugated succinyl Con A binds to neonatal erythrocytes but does not induce endocytosis; if, however, antibodies to ferritin are now added, endocytosis occurs. These results are consistent with a greater lateral mobility of at least a fraction of Con A recptors in the membrane of the intact neonatal erythrocyte compared to the adult. The results also support the hypothesis that the clustering of receptors is obligatory for endocytosis to occur. No discernible difference was found in the sodium dodecyl sulfate/polyacrylamide gel patterns of the membrane proteins of the neonatal and adult cells.