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Ontogeny of renal sulfate transporters: postnatal mRNA and protein expression
1Department of Physiology and Pharmacology, The University of Queensland, Brisbane, Queensland 4072, Australia. danielm@plpk.uq.edu.au
Insights
During postnatal development, renal sulfate transporter (NaS(i)-1 and sat-1) mRNA and protein levels change. Sat-1 protein levels mirror mRNA changes, while NaS(i)-1 protein remains constant, suggesting distinct regulatory mechanisms.
Area of Science:
- Nephrology
- Molecular Biology
- Developmental Biology
Background:
- Renal reabsorption of inorganic sulfate is crucial for maintaining sulfate homeostasis.
- Sulfate transport in the proximal tubule is mediated by specific transporters, including NaS(i)-1 and sat-1.
- The developmental regulation of these transporters during postnatal maturation is not well understood.
Purpose of the Study:
- To investigate the ontogeny of renal sulfate transporter (NaS(i)-1 and sat-1) expression during postnatal maturation in rats.
- To determine how the expression levels of NaS(i)-1 and sat-1 mRNA and proteins change from day 1 to day 77 postnatally.
- To explore the functional changes in sulfate transport associated with these developmental changes.
Main Methods:
- Quantitative analysis of NaS(i)-1 and sat-1 mRNA levels using RT-PCR.
- Assessment of sodium-dependent and sodium-independent sulfate uptake using Xenopus oocyte expression system.
- Western blot analysis to determine NaS(i)-1 and sat-1 protein levels in renal membranes.
Main Results:
- Both NaS(i)-1 and sat-1 mRNA levels significantly increased postnatally, peaking at day 14, with a tenfold increase compared to day 1.
- Functional sulfate uptake studies in Xenopus oocytes showed a similar age-dependent increase in both sodium-dependent and sodium-independent sulfate transport.
- While NaS(i)-1 protein levels remained relatively constant throughout postnatal development, sat-1 protein levels paralleled its mRNA expression, increasing until day 14 and then declining.
Conclusions:
- Renal sulfate transporter expression undergoes significant changes during postnatal maturation.
- Sat-1 protein expression is tightly regulated by its mRNA levels, indicating post-transcriptional control.
- NaS(i)-1 protein levels are maintained independently of mRNA changes, suggesting post-translational or translational regulatory mechanisms are involved in ensuring consistent proximal tubular membrane expression during maturation.
Abstract:
Renal reabsorption of inorganic sulfate changes during growth and development. We have studied the expression of two proximal tubular sulfate transporters, NaS(i)-1 and sat-1, during postnatal maturation. Both NaS(i)-1 and sat-1 mRNA levels increase postnatally, peaking at day 14, with a maximal tenfold increase in NaS(i)-1 and sat-1 mRNA levels compared with day 1. A similar age-dependent increase was observed for sodium-dependent and sodium-independent sulfate uptakes by injection of rat kidney mRNA into Xenopus oocytes. Western blot analysis of renal membranes from rats aged day 1 to day 77 showed no significant changes for NaS(i)-1 protein, whereas sat-1 protein levels paralleled mRNA expression, increasing from day 1 to day 14, followed by a decrease in protein levels thereafter. For NaSi-1 protein expression, translational or posttranslational mechanisms may maintain equal numbers of sulfate proteins on proximal tubular membranes during maturation, whereas sat-1 protein levels are in close agreement with mRNA changes. This is the first study to look at the ontogeny of renal sulfate transporter (NaS(i)-1 and sat-1) expression during postnatal maturation.