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Glutamine fructose-6-phosphate aminotransferase and glycoprotein synthesis in the developing chick eye
Insights
Glutamine fructose-6-phosphate aminotransferase activity is high in early chick embryos, crucial for cell differentiation. This enzyme
Area of Science:
- Biochemistry
- Developmental Biology
- Ophthalmology
Background:
- Glutamine fructose-6-phosphate aminotransferase (GFPT) is vital for glycoprotein synthesis.
- Retinal development involves cell migration, differentiation, and adhesion.
- The chick embryo provides a model for studying ocular development and cell adhesion.
Purpose of the Study:
- To investigate the role of GFPT and complex carbohydrates in chick embryo retinal development and adhesion.
- To measure GFPT activity during critical stages of retinal differentiation and adhesion.
- To assess the impact of glycoprotein synthesis inhibitors on retinal adhesion.
Main Methods:
- Measurement of GFPT specific activity in chick embryo posterior ocular tissues (retina, retinal pigment epithelium).
- Assay of glucosamine incorporation into retinal macromolecules.
- Histological examination of the interphotoreceptor matrix (IPM) for glycosaminoglycans.
- Testing the effects of glycoprotein synthesis inhibitors on retinal adhesion.
Main Results:
- GFPT activity was high in early development, decreasing significantly by day 9.
- Peak GFPT activity coincided with retinal cell migration and differentiation.
- No evidence linked complex carbohydrates or glycosaminoglycans in the IPM to retinal adhesion.
- Glycoprotein synthesis inhibitors did not affect retinal adhesion.
Conclusions:
- GFPT activity is developmentally regulated and highest during key retinal maturation phases.
- Complex carbohydrates and glycosaminoglycans are not essential for neural retina-PE adhesion in chick embryos.
- Retinal adhesion in chick embryos appears to be independent of cell-surface glycoproteins and IPM composition.
Abstract:
Glutamine fructose-6-phosphate aminotransferase is an essential enzyme in the synthesis of glycoproteins and other complex carbohydrates. The specific activity of this enzyme was measured in posterior ocular tissues of the chick embryo from day 6 of development until hatching. The enzyme is present at high concentrations in the early embryo, then decreases 15-fold by day 9 in both retina and retinal pigment epithelium (PE). Thus, aminotransferase activity is highest during the period when retinal cells are migrating and beginning to differentiate; these maturational events may require cell-surface glycoproteins. On day 17-18 of chick embryo development, the neural retina suddenly adheres firmly and irreversibly to the underlying PE. Aminotransferase activity and glucosamine incorporation into retinal macromolecules were examined near this critical time, as were the effects of glycoprotein-synthesis inhibitors upon retinal adhesion. No evidence was found for involvement of complex carbohydrates (on cell surfaces or in the interphotoreceptor matrix, IPM) in formation of retinal adhesion in the chick. Histological studies show an absence of glycosaminoglycans in the IPM of embryonic chicks (at all stages) and of adult chickens, although these compounds are present in mammalian matrix.
