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Differential regulation of platelet-derived growth factor genes in fetal rat lung fibroblasts
1Medical Research Council Group in Lung Development, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.
Insights
Fetal lung fibroblasts produce platelet-derived growth factor (PDGF)-AA, PDGF-BB, and PDGF beta-receptor. Their gene expression is differentially regulated during fetal lung development, impacting morphogenesis.
Area of Science:
- Developmental Biology
- Cell Biology
- Molecular Biology
Background:
- Platelet-derived growth factor (PDGF) is implicated in fetal lung development.
- The specific cells producing PDGF and its receptors in the fetal lung are not well-defined.
Purpose of the Study:
- To investigate the developmental expression of PDGF and its receptor genes in fetal rat lung fibroblasts.
- To determine the cellular sources and target cells of PDGF within the developing fetal lung.
Main Methods:
- Northern analysis to detect PDGF A-chain, B-chain, and beta-receptor mRNAs.
- Immunocytochemistry and metabolic labeling to confirm protein expression.
- Affinity cross-linking to identify PDGF beta-receptors.
- Analysis of gene expression from Day 19 to Day 21 of gestation.
Main Results:
- Fetal lung fibroblasts express PDGF A-chain, B-chain, and beta-receptor genes and proteins.
- PDGF A-chain expression remained constant, while PDGF-AA was the major secreted form.
- PDGF B-chain expression peaked during the early canalicular stage (Day 19) due to increased transcription and mRNA stability.
- PDGF beta-receptor mRNA levels were constant, suggesting balanced synthesis and degradation.
Conclusions:
- Fetal lung fibroblasts synthesize PDGF-AA, PDGF-BB, and PDGF beta-receptor.
- Differential regulation of PDGF gene expression occurs during late fetal lung development.
- These findings contribute to understanding PDGF's role in fetal lung morphogenesis.
Abstract:
There is increasing evidence to suggest that platelet-derived growth factor (PDGF), or PDGF-like molecules, play a role in fetal lung morphogenesis. The cellular sources of PDGF and its target cells within the fetal lung remain to be defined. In the present study, we investigated the developmental expression of PDGF and its cognate receptor genes in fetal rat lung fibroblasts. Northern analysis revealed that fetal lung fibroblasts express the PDGF A-chain, B-chain, and beta-receptor genes. The cells actively translated these mRNAs into protein as demonstrated by immunocytochemistry and by metabolic labeling with [35S]methionine, followed by immunoprecipitation with specific PDGF-AA and -BB antibodies. Affinity cross-linking with 125I-labeled PDGF-BB demonstrated the presence of PDGF beta-receptors on fetal lung fibroblasts. The development expression of the PDGF genes was examined in fibroblasts derived from the early canalicular (Day 19) to the early saccular stage (Day 21) of lung development (term = 22 days). PDGF A-chain gene expression was at a low but constant level during late gestation. No change in either the transcription rate or stability of the message for this gene was observed with advancing gestation. Despite these mRNA observations, PDGF-AA is the major secreted form in the medium of the fibroblasts. Expression of PDGF B-chain gene was greatest during the early canalicular stage (Day 19) and declined sharply thereafter. The greater expression of PDGF B-chain during the canalicular stage was due to a greater rate of transcription and a greater PDGF B-chain mRNA stability. The PDGF beta-receptor gene was expressed at a lower but constant level in these cells during late gestation. The constant level of PDGF beta-receptor mRNA could be attributed to a balanced increased synthesis of the message coupled to an increased breakdown of the transcript. These data indicate that fetal lung fibroblasts synthesize PDGF-AA, PDGF-BB, and PDGF beta-receptor and that they regulate the developmental expression of these PDGF genes differently.