Effects of cytosine arabinoside on differential gene expression in embryonic neural retina. I. Accumulation of glutamine synthetase with suppression of macromolecular synthesis.

The analogue of cytidine, cytosine arabinoside (Ara-C), elicited a significant increase in the level of glutamine synthetase (GS) in embryonic chick neural retina in the absence of the steroid inducer of the enzyme. The increase was due to de novo synthesis of GS and was mediated by RNA which accumulated in the presence of the effective concentration of Ara-C. Accumulation of GS did not result from the inhibition of DNA synthesis for which Ara-C is best known.

Cell-surface interactions: differential inhibition by proflavine of embryonic cell aggregation and production of specific cell-aggregating factor.

Cell recognition and morphogenetic aggregation of embryonic cells into tissues are mediated by specific macromolecules in the cell surface (cell-aggregating factors). A factor specific for embryonic neural retina cells was demonstrated; its synthesis is required for histotypic reaggregation of retina cell suspensions. We show that proflavine (3,6-diaminoacridine) preferentially and reversibly suppresses production of the cell-aggregating factor and thereby inhibits normal cell reaggregation.

Glutamine synthetase induction in embryonic neural retina: immunochemical identification of polysomes involved in enzyme synthesis.

Glutamine synthetase (EC 6.3.1.

Preferential inhibition by proflavine of the hormonal induction of glutamine synthetase in embryonic neural retina.

The hormonal induction of glutamine synthetase (EC 6.3.1.

Tissue-specific cell-surface antigens in embryonic cells.

With the use of antisera prepared in rabbits against suspensions of live embryonic chick tissue cells, qualitative differences in cell surface antigens were demonstrated on cells from different embryonic chick tissues by immune agglutination and immunofluorescence. Unabsorbed antisera reacted with both homologous and nonhomologous cells; thorough absorption of the antisera with heterologous tissues removed cross-reacting antibodies, and the antisera acquired a high degree of tissue specificity. Thus, antiretina cell serum absorbed with nonretina cells or tissues, agglutinated only neural retina cells, and was shown by immunofluorescence tests to react specifically with the surface of retina cells, both in cell suspensions and in frozen tissue sections.

Changes in macromolecular synthesis associated with the induction of glutamine synthetase in embryonic retina.

The hydrocortisone-mediated induction of glutamine synthetase in the neural retina of chicken embryo in vitro is correlated with enhanced incorporation into protein of [(14)C]aspartic acid, an amino acid abundant in this enzyme. In the induced retina labeled with [(14)C]aspartic acid, a peak of radioactivity was detected in the region of the polysomal profile corresponding to polysomes comprising 12-14 ribosomes. In retinas labeled with [(3)H]uridine, an increased amount of radioactivity was also detected in the same polysomal region of the hydrocortisone-induced retina.

Embryonic and neoplastic cell surfaces: availability of receptors for concanavalin A and wheat germ agglutinin.

Embryonic tissue cells dissociated with ethylenediaminetetraacetate are readily agglutinated by the carbohydrate-binding protein concanavalin A. In this property, they resemble transformed, neoplastic cells; and they differ from untransformed adult cells, which are agglutinated by concanavalin A only after their receptors are unmasked by proteolytic treatment. Receptor sites for wheat germ agglutinin are also present on the surface of embryonic cells, but in a masked form, as on untransformed adult culture cells; they can be unmasked by treatment of the cells with trypsin.