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Differential expression of transforming growth factor-beta receptors in rat kidney development
M E Choi1, A Liu, B J Ballermann
1Division of Nephrology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Abstract:
Transforming growth factor-beta 1 (TGF-beta 1) is strongly expressed during embryogenesis and in sites undergoing intense development and morphogenesis. Two receptor serine/threonine kinases (types I and II) have been identified as signal-transducing TGF-beta receptors. This study was undertaken to further explore the role of the distinct TGF-beta receptors during kidney development. The species-specific sequence information for the two T beta R-I, namely, activin receptor-like kinase-5 (ALK-5) and Tsk7L, in the rat was sought. Two full-length T beta R-I cDNAs were cloned from a neonatal rat kidney and lung libraries, and sequencing revealed that they were the rat homologs of human ALK-5 and murine Tsk7L. Both types I and II TGF-beta receptors are expressed in the kidney as determined by Northern blot analysis. T beta R-II mRNA abundance was significantly greater in the neonatal rat kidney compared with the adult rat kidney. Similarly, ALK-5 mRNA was more highly expressed in the fetal and neonatal rat kidney than the adult rat kidney. In contrast, there was no significant difference in Tsk7L mRNA abundance among the fetal, neonatal, and adult rat kidney. Thus, based on these findings, both T beta R-II and ALK-5 are developmentally regulated in the kidney. Increased expression of T beta R-II and ALK-5 proteins in the developing kidney was confirmed by immunohistochemistry. Interestingly, the two TGF-beta receptors did not entirely colocalize, raising the intriguing possibility that other TGF-beta signaling receptors may be involved.
Insights
Transforming growth factor-beta (TGF-beta) receptors T beta R-II and activin receptor-like kinase-5 (ALK-5) are developmentally regulated in the rat kidney. Their expression is higher in fetal and neonatal kidneys than in adult kidneys.
Area of Science:
- Developmental Biology
- Molecular Biology
- Renal Physiology
Background:
- Transforming growth factor-beta 1 (TGF-beta 1) is crucial for embryogenesis and tissue morphogenesis.
- Two types of serine/threonine kinase receptors, Type I and Type II, mediate TGF-beta signaling.
- Understanding TGF-beta receptor roles in kidney development is essential.
Purpose of the Study:
- To investigate the distinct roles of TGF-beta receptors during kidney development.
- To identify and characterize rat homologs of Type I TGF-beta receptors, specifically activin receptor-like kinase-5 (ALK-5) and Tsk7L.
Main Methods:
- Cloning of full-length T beta R-I cDNAs (ALK-5 and Tsk7L) from neonatal rat kidney and lung libraries.
- Northern blot analysis to determine mRNA abundance of T beta R-II, ALK-5, and Tsk7L in fetal, neonatal, and adult rat kidneys.
- Immunohistochemistry to confirm protein expression levels of T beta R-II and ALK-5 in developing kidneys.
Main Results:
- Rat homologs of human ALK-5 and murine Tsk7L were identified.
- Both T beta R-II and ALK-5 mRNA levels were significantly higher in neonatal rat kidneys compared to adult kidneys.
- Tsk7L mRNA abundance showed no significant difference across developmental stages.
- Increased T beta R-II and ALK-5 protein expression was observed in the developing kidney.
- The two TGF-beta receptors did not show complete colocalization.
Conclusions:
- T beta R-II and ALK-5 are developmentally regulated in the rat kidney.
- Their elevated expression during fetal and neonatal stages suggests a critical role in kidney development.
- The partial colocalization of T beta R-II and ALK-5 indicates potential involvement of other TGF-beta signaling receptors.