Glomerular laminin isoform transitions: errors in metanephric culture are corrected by grafting.
Glomerular basement membrane (GBM) assembly and maturation are marked by the replacement of laminin-1 (containing alpha 1-, beta 1-, and gamma 1-chains) with laminin-11 (consisting of alpha 5-, beta 2-, and gamma 1-chains). Similarly, the alpha 1- and alpha 2-chains of type IV collagen are replaced by collagen alpha 3-, alpha 4-, and alpha 5(IV)-chains. The cellular origins of these molecules and mechanisms for isoform removal and substitution are unknown. To explore glomerular laminin isoform transitions in vitro, we assessed metanephric organ cultures. Standard culture conditions do not support endothelial cell differentiation, and glomerular structures that form in vitro are avascular. Nevertheless, extensive podocyte development occurs in these cultures, including the formation of foot processes and assembly of a GBM-like matrix. Here, we show that the podocyte-specific markers, glomerular epithelial protein 1 and nephrin, which are normally expressed in capillary loop stage glomeruli in vivo, are also expressed by glomerular figures that form in organ culture. However, the GBM-like segments that form in vitro do not undergo normal laminin isoform switching. Instead, both laminin alpha 1- and alpha 5-chains are present, as is the beta 1-chain, but not beta 2. When avascular organ-cultured kidneys are grafted into anterior eye chambers, however, kidney-derived angioblasts establish extensive vasculature by 6 days, and glomeruli are lined by endothelial cells. We evaluated embryonic day 12 (E12) vascular endothelial growth factor receptor (Flk1)-lacZ kidneys that had first been grown in organ culture for 6--7 days and then grafted into wild-type mice. Correct laminin isoform substitution occurred and correlated with the appearance of endothelial cells expressing Flk1. Our findings indicate that endothelial cells, and/or factors present in the circulation, mediate normal GBM laminin isoform transitions in vivo.
Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, Kansas 66160-7400, USA.
P L
PL
St  John
R
R
Wang
Y
Y
Yin
J H
JH
Miner
B
B
Robert
D R
DR
Abrahamson
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D001485:Basement Membrane / Q000737:chemistry / Q000502:physiology; D002196:Capillaries / Q000648:ultrastructure; D004730:Endothelium, Vascular / Q000648:ultrastructure; D000939:Epitopes / Q000032:analysis; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D007536:Isomerism; D007678:Kidney Glomerulus / Q000166:cytology / Q000502:physiology / Q000637:transplantation; D016030:Kidney Transplantation / Q000379:methods; D007763:Lac Operon; D007797:Laminin / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D008565:Membrane Proteins / Q000032:analysis; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009399:Nephrons / Q000502:physiology / Q000637:transplantation / Q000648:ultrastructure; D009924:Organ Culture Techniques; D017027:Protein Tyrosine Phosphatases / Q000032:analysis; D011506:Proteins / Q000032:analysis; D011784:Quail; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3; D017978:Receptors, Growth Factor / Q000235:genetics; D040262:Receptors, Vascular Endothelial Growth Factor
D000911:Antibodies, Monoclonal; D000939:Epitopes; D007797:Laminin; D008565:Membrane Proteins; D011506:Proteins; D017978:Receptors, Growth Factor; C113267:nephrin; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor; D017027:Protein Tyrosine Phosphatases; C516890:Ptpro protein, mouse; D054631:Receptor-Like Protein Tyrosine Phosphatases, Class 3