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Fibroblast growth factor receptor levels decrease during chick embryogenesis
1Department of Biochemistry, University of Wisconsin, Madison 53706.
Abstract:
Two putative receptors for fibroblast growth factor (FGF) of approximately 150 and 200 kD were identified in membrane preparations from chick embryos. Specific binding (femtomoles/milligram) of 125I-aFGF to whole chick embryonic membranes was relatively constant from day 2 to 7, then decreased fivefold between days 7 and 13. Day-19 chick embryos retained 125I-aFGF binding at low levels to brain, eye, and liver tissues but not to skeletal muscle or cardiac tissues. The 200-kD FGF receptor began to decline between day 4.5 and 7 and was barely detectable by day 9, whereas the 150-kD FGF receptor began to decline by day 7 but was still detectable in day-9 embryonic membranes. It is not known whether the two FGF-binding proteins represent altered forms of one polypeptide, but it is clear that their levels undergo differential changes during development. Because endogenous chick FGF may remain bound to FGF receptor in membrane preparations, membranes were treated with acidic (pH 4.0) buffers to release bound FGF; such treatment did not affect 125I-aFGF binding and moderately increased the number of binding sites in day-7 and -19 embryos. Consequently, the observed loss of high affinity 125I-aFGF binding sites and FGF-binding polypeptides most likely represents a loss of FGF receptor protein. These experiments provide in vivo evidence to support the hypothesis that regulation of FGF receptor levels may function as a mechanism for controlling FGF-dependent processes during embryonic development.
Insights
Fibroblast growth factor (FGF) receptor levels decrease significantly during chick embryonic development. This decline in FGF receptors suggests a regulatory mechanism controlling FGF-dependent developmental processes.
Area of Science:
- Developmental Biology
- Molecular Biology
- Cell Signaling
Background:
- Fibroblast growth factor (FGF) plays a crucial role in embryonic development.
- FGF signaling is mediated by specific FGF receptors on cell membranes.
- Understanding FGF receptor dynamics is key to deciphering developmental regulation.
Purpose of the Study:
- To investigate the developmental changes in FGF receptor expression in chick embryos.
- To determine if changes in FGF receptor levels correlate with developmental stages.
- To explore the potential role of FGF receptor regulation in controlling FGF-dependent processes.
Main Methods:
- Identification and quantification of FGF receptors (150-kD and 200-kD) in chick embryonic membrane preparations.
- Radioligand binding assays using 125I-labeled FGF (125I-aFGF) at different embryonic days (2-19).
- Acidic buffer treatment (pH 4.0) to assess the impact on FGF receptor binding.
Main Results:
- Two FGF receptor proteins (150-kD and 200-kD) were identified.
- Specific binding of 125I-aFGF was high from day 2-7, then decreased significantly by day 13.
- The 200-kD receptor declined early (by day 9), while the 150-kD receptor persisted longer.
- Low binding levels were observed in day-19 embryos in brain, eye, and liver tissues.
Conclusions:
- FGF receptor levels undergo differential changes during chick embryonic development.
- The observed decrease in FGF receptor protein suggests a regulatory mechanism.
- Regulation of FGF receptor levels is a likely mechanism for controlling FGF-dependent embryonic development.