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Ontogenesis of 28 kDa vitamin D-induced calcium-binding protein in human kidney
Insights
This study tracked 28 kDa vitamin D-induced calcium binding protein (CaBP) in developing kidneys. CaBP is synthesized early in fetal kidneys, with its distribution changing as the organ matures.
Area of Science:
- Nephrology
- Developmental Biology
- Biochemistry
Background:
- The 28 kDa vitamin D-induced calcium binding protein (CaBP) plays a role in calcium transport.
- Understanding the developmental expression of CaBP in the kidney is crucial for comprehending renal calcium homeostasis.
- Previous studies have not fully elucidated the precise localization and developmental changes of CaBP in the human fetal kidney.
Purpose of the Study:
- To investigate the kidney distribution and subcellular localization of 28 kDa CaBP during human fetal development.
- To examine the changes in CaBP expression patterns with kidney maturation from fetal stages to adulthood.
- To determine the cellular sites of CaBP synthesis in the developing kidney.
Main Methods:
- Immunocytochemistry was employed to study CaBP distribution in fetal and adult kidney tissues.
- Immunoelectronmicroscopy was used for subcellular localization of CaBP.
- A specific antibody to rat renal 28 kDa CaBP was utilized.
Main Results:
- 28 kDa CaBP was detected in all kidneys from the eleventh week of gestation.
- Early fetal kidneys showed homogeneous staining in deep collecting ducts and intense labeling in some deep cortical distal tubules.
- With kidney maturation, CaBP labeling decreased in collecting ducts and increased in distal tubular cells; it was found in cytosol and nuclear euchromatin.
Conclusions:
- 28 kDa CaBP is synthesized early in fetal kidney development.
- The expression of 28 kDa CaBP is transient in deep collecting duct cells during early fetal life.
- Distal tubular cells progressively increase their synthesis of 28 kDa CaBP as the kidney matures.
Abstract:
The kidney distribution of 28 kDa vitamin D-induced calcium binding protein (CaBP) was studied in 15 fetuses (11 to 33 weeks old), six children and adults (12 days to 32 years old) by immunocytochemistry using a specific antibody to rat renal 28 kDa CaBP. Similar results were obtained on frozen and fixed tissues. Kidneys from one adult and three fetuses were studied by immunoelectronmicroscopy for antigen localization at the subcellular level using the indirect immunoperoxidase technique. The 28 kDa CaBP was present in all kidneys from the eleventh week of gestation. At that stage, all deep parts of collecting ducts were homogeneously stained and a few distal tubules located in the deep cortex were intensely labeled. No labeling was observed in the early stage of nephron differentiation (S-body). 28 kDa CaBP distribution changed with kidney maturation. There was a progressive reduction of the deep part of collecting duct labeling and a concomitant increase in the number and intensity of stained distal tubular cells. At the ultrastructural level, 28 kDa CaBP was observed in the cytosol and the nuclear euchromatin. Our study demonstrates the early cellular synthesis of 28 kDa CaBP and its transient expression by deep collecting duct cells during early fetal life, at a time when only a few distal convoluted tubular cells synthetize it.