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Secretion and glycosylation of alpha-foetoprotein by the mouse yolk sac
Abstract:
Secretion and glycosylation of alpha-foetoprotein (AFP) by mouse yolk sac were studied by using yolk-sac explants cultured in vitro. Yolk-sac explants rapidly incorporated [35S]methionine into AFP, whereas radioactively labelled AFP was not found in the medium until 30 min after incubation was initiated. Electrophoretic analysis revealed that microheterogeneity of AFP synthesized in explants increased in parallel with the gestational age of the yolk sacs. The change in microheterogeneity was noted by the formation of increasingly acidic forms. Only the most acidic forms of AFP were found to be present in the medium on each gestational day studied. Tunicamycin reduced the incorporation of glucosamine into AFP with a concomitant decrease in molecular weight and microheterogeneity. However, the relative amount of AFP released into the medium was not altered by the presence of tunicamycin. The presence of under-glycosylated AFP in the medium indicates that glycosylation of AFP is not essential for its secretion from the yolk sac. In light of these and previous findings, it is suggested that the glycosylation of AFP may be important for the turnover of this glycoprotein in serum.
Insights
Mouse yolk sac secretion of alpha-fetoprotein (AFP) was studied. Glycosylation is not essential for AFP secretion, but may influence its serum turnover.
Area of Science:
- Biochemistry
- Developmental Biology
- Glycobiology
Background:
- Alpha-fetoprotein (AFP) is a major fetal serum protein.
- Its synthesis and secretion by the yolk sac are critical during embryonic development.
Purpose of the Study:
- To investigate the relationship between alpha-fetoprotein (AFP) secretion and glycosylation in mouse yolk sac explants.
- To determine if glycosylation is essential for AFP secretion or affects its molecular characteristics.
Main Methods:
- In vitro culture of mouse yolk sac explants.
- Incorporation of [35S]methionine to label newly synthesized AFP.
- Electrophoretic analysis to assess AFP microheterogeneity and molecular weight.
- Treatment with tunicamycin to inhibit glycosylation.
Main Results:
- Yolk sac explants rapidly synthesized and secreted AFP.
- AFP microheterogeneity increased with gestational age, with more acidic forms appearing in the medium.
- Tunicamycin treatment reduced AFP glycosylation and molecular weight but did not affect secretion rates.
- Under-glycosylated AFP was detected in the culture medium.
Conclusions:
- Glycosylation of AFP is not a prerequisite for its secretion from the mouse yolk sac.
- The observed changes in AFP microheterogeneity suggest developmental regulation of glycosylation.
- Glycosylation may play a role in the subsequent turnover or function of AFP in serum.