Genetic disorders – Development
Kidney International (2000) 57, 1847–1859; doi:10.1046/j.1523-1755.2000.00034.x
Molecular cloning, expression, and distribution of glomerular epithelial protein 1 in developing mouse kidney
Ruixue Wang, Patricia L St John, Matthias Kretzler, Roger C Wiggins and Dale R Abrahamson
Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama, USA; Medical Policlinic, University of Munich, Munich, Germany; Division of Nephrology, University of Michigan Medical Center, Ann Arbor, Michigan, and Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, Kansas, USA
Correspondence: Dale R. Abrahamson, Ph.D., Department of Anatomy and Cell Biology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, Kansas 66160-7400, USA. E-mail: dabrahamson@kumc.edu
Received 12 August 1999; Revised 17 November 1999; Accepted 5 December 1999.
Abstract
Molecular cloning, expression, and distribution of glomerular epithelial protein 1 in developing mouse kidney.
Background
Glomerular epithelial protein 1 (GLEPP1) is a receptor-like membrane protein tyrosine phosphatase (RPTP) with a large ectodomain consisting of multiple fibronectin type III repeats, a single transmembrane segment, and a single cytoplasmic phosphatase active site sequence. In adult human and rabbit kidneys, GLEPP1 is found exclusively on apical membranes of podocytes and especially on surfaces of foot processes. Although neither ligand nor function for this protein is known, other RPTPs with similar topologies have been implicated in mediating adherence behavior of cells.
Methods
To evaluate potential roles of GLEPP1 further, we cloned the full-length mouse GLEPP1 cDNA and examined its expression patterns in developing kidney by Northern blot analysis, in situ hybridization, and immunofluorescence microscopy.
Results
Nucleotide sequencing showed that mouse GLEPP1 was approximately 80% identical to rabbit and human GLEPP1 and approximately 91% identical at the amino acid level. The membrane-spanning and phosphatase domains of mouse GLEPP1 shared> 99% homology with PTP
, a murine macrophage cytoplasmic phosphatase. Northern analysis identified a single GLEPP1 transcript of approximately 5.5 kb in fetal kidney that became approximately threefold more abundant in adults. In situ hybridization of newborn mouse kidney revealed GLEPP1 mRNA in visceral epithelial cells (developing podocytes) of comma- and S-shaped nephric figures, and expression increased in capillary loop and maturing stage glomeruli. Beginning on embryonic day 14, GLEPP1 protein was first observed on cuboidal podocytes of capillary loop stage glomeruli, but nascent podocytes of earlier comma- and S-shaped nephric figures were negative. At later stages of glomerular maturation, where foot process elongation and interdigitation occurs, GLEPP1 immunolabeling intensified on podocytes and then persisted at high levels in fully developed glomeruli.
Conclusion
Our findings are consistent with a role for GLEPP1 in mediating and maintaining podocyte differentiation specifically.
Keywords:
glomerulus, podocyte, phosphatase, kidney development, cell function
