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Biomedical subjects

A A Moscona

Publications and source records attributed to A A Moscona.

At least 73 records · Page 4Linked to original sources
PubMed1976

Stimulation of DNA synthesis by ouabain and concanavalin A in cultures of embryonic neural retina cells.

Ouabain and concanavalin A, agents which bind to specific sites in the cell membrane, stimulate DNA synthesis and cell replication in monolayer cultures of neural retina cells from late chick embryos. The results suggest a relationship between control of retina cell replication and properties of the cell membrane. The experiments involved measurements of 3H-thymidine incorporation in primary monolayer cultures (24-48h) of retina cells from embryos of different ages. Stimulation by ouabain was greatest in cells from 14-day embryos, and its magnitude was similar to that elicited in these cell cultures by concanavalin A. Simultaneous treatment of 14-day retina cells with both agents resulted in a greater than additive stimulation of DNA synthesis. Our results demonstrated that, although during normal embryogenesis cell replication in the neural retina has virtually ceased by day 14 of development, some cells retained a capacity for mitogenesis when exposed to conditions such as provided in these experiments. By autoradiography the responding cells were identified as large epithelioid retina cells (LER cells). Under optimal conditions of simultaneous treatment with ouabain and Con A about 20% of the LER cells showed stimulation of DNA synthesis. The nature of LER cells and other aspects of our findings are discussed.

Animals↗
PubMed1976

Isolation of retina-specific cell-aggregating factor from membranes of embryonic neural retina tissue.

There is increasing evidence that developmental associations among embryonic cells are mediated by specific components of the cell surface. Earlier work has indicated that such components are extruded into the medium of primary monolayer cultures of embryonic cells, and that they represent the active constituents of the tissue-spedific cell-aggregating factors isolated fro- the supernatant medium of such cultures. We presently report that tissue-specific cell-aggregating factors can be obtained directly from embryonic tissues, and describe the isolation and partial purification of retina-spedific factor from a cell-membrane preparation derived from retina tissue of the chick embryo. Extraction of the purified membrane preparation with 1-butanol yielded an activity in the aqueous phase which resides in a protein probably a glycoprotein, with an estimated molecular weight of 50,000 in solution. This material could be obtained from retinas of embryos not older than 13 days, and only pre-13-day cells responded to its cell-aggregating activity. By these characteristics, this membrane-derived retina factor closely resembles the retina cell-aggregating glycoprotein previously purified from the supernatant medium of retina cell cultures. It is of special interest that the cell-aggregating protein is obtainable from cellular membranes during those stages of development when retina cells are most actively engaged in histological organization. Work in progress indicates that, by the procedures described herein, tissue-specific cell-aggregating factors can also be obtained from membrane preparations of other embryonic tissues.

Age Factors↗
PubMed1975

Purification and characterization of the retina-specific cell-aggregating factor.

The tissue-specific, cell-aggregating component of embryonic neural retina cells was purified from the retina cell-aggregating factor and characterized as a glycoprotein. Its molecular weight in solution is in the range of 50,000, and it contains 10-15% carbohydrate. The amino-acid and carbohydrate compositions have been determined. The glycoprotein is produced by embryonic neural retina cells in primary monolayered cultures and is released into the medium. Its tissue-specific, cell-aggregating effect requires integrity of the polypeptide portion, but not of the carbohydrate portion. We suggest that the isolated molecule is a specific determinant of the embryonic retina cell-surface and that it is involved in mediating self-recognition and selective adhesiveness of these cells.

Amino Acids↗
PubMed1974

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. This new effect of Ara-C involves differential suppression of macromolecular synthesis in this system: the concentration of Ara-C which caused maximum GS accumulation suppressed overall protein and RNA syntheses 65-75% without inhibiting the transcription and translation of templates essential for GS synthesis. Withdrawal of Ara-C resulted in restoration of RNA synthesis and cessation of GS accumulation, even though preformed templates for the enzyme were present; however, if all RNA synthesis was arrested with actinomycin D at the time of Ara-C withdrawal, GS continued to accumulate. The results are consistent with the hypothesis that Ara-C differentially affects the activity of structural and regulatory genes involved in the regulation of GS levels in the retina: Ara-C allows transcription of the enzyme-specific templates, but reversibly inhibits the expression of regulatory genes which limit the accumulation of GS.

Animals↗