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Gene expression in derivatives of embryonic foregut during prenatal development of the rat
J W Gaasbeek Janzen1, P J Westenend, R Charles
1Department of Anatomy and Embryology, University of Amsterdam, The Netherlands.
Insights
Enzymes like carbamoylphosphate synthetase (CPS) and arginase appear synchronously in developing rat organs. Fetal liver cells show heterogeneous enzyme distribution, linked to vascularization and cell-specific synthesis timing.
Area of Science:
- Developmental Biology
- Molecular Biology
- Biochemistry
Background:
- Understanding the developmental expression of key metabolic enzymes is crucial for comprehending organogenesis.
- Previous assumptions suggested fetal hepatocytes form a homogeneous cell population regarding enzyme content.
Purpose of the Study:
- To investigate the spatio-temporal expression patterns of specific adult cellular phenotype proteins in rat embryos and fetuses.
- To examine the heterogeneity of enzyme distribution in developing liver cells.
Main Methods:
- Immunohistochemical analysis of rat embryos and fetuses at distinct developmental stages.
- Focus on proteins: carbamoylphosphate synthetase (CPS), arginase, glutamate dehydrogenase (GLDH), and amylase.
Main Results:
- Synchronous appearance of enzyme subsets in foregut derivatives suggests common regulatory factors.
- Arginase and CPS exhibit heterogeneous distribution in fetal hepatocytes between embryonic day (ED) 16 and ED 20, linked to liver vascular architecture.
- Intercellular heterogeneity in CPS content, unrelated to vasculature, observed from ED 14 to ED 20, indicating temporal differences in cellular enzyme accumulation.
Conclusions:
- Gene expression for these enzymes in different organs may be regulated by common factors during development.
- Fetal hepatocytes are not a homogeneous cell population, displaying heterogeneous enzyme distribution influenced by vascularization and asynchronous cellular enzyme synthesis.
- This heterogeneity resolves perinatally due to stimulated enzyme synthesis.
Abstract:
Proteins characteristic for the adult cellular phenotype, i.e., carbamoylphosphate synthetase (CPS) for liver and small intestine, arginase for liver, glutamate dehydrogenase (GLDH) for pancreas, liver, and small intestine, and amylase for pancreas were studied immunohistochemically in rat embryos and fetuses. At distinct developmental stages, subsets of enzymes appear synchronously in the foregut derivatives, suggesting that gene expression in the different organs is regulated by common factors. In contrast to the long-held opinion that fetal hepatocytes are a homogeneous cell population, it is shown that arginase and CPS are heterogeneously distributed between ED 16 and ED 20. This heterogeneity is related to the vascular architecture of the liver and disappears perinatally as the result of strong stimulation of enzyme synthesis. In addition, an intercellular heterogeneity in CPS content that is not related to the vasculature is observed between ED 14 and ED 20. This "random" heterogeneity reflects temporal differences in the onset of CPS accumulation in individual cells.