|Ph.D Student||Soueid-Baumgarten Sharon|
|Subject||Molecular Regulation of Kidney Differentiation in the Chick|
Mesonephros Model System
|Department||Department of Medicine||Supervisor||Professor Thomas Schultheiss|
|Full Thesis text|
The kidneys are bilateral organs that regulate the composition and volume of body fluids, and eliminate metabolic waste products. The basic functional unit of the kidney is the nephron, in which blood filtration occurs. The filtrate drains into the collecting duct and is disposed through the urine.
Three kidneys are sequentially formed during embryonic development: the pronephros and mesonephros, which degenerate during embryonic development, and the metanephros - the adult kidney. During development, the duct extends caudally by migration and proliferation of anterior cells. The metanephros is formed by inductive interactions between the mesenchymal cells and the duct after its caudal extension. Mesonephros formation occurs similarly to metanephros formation, however it exhibits a simpler structure.
We first aimed to describe the expression pattern during normal mesonephros development of regulatory molecules known to be involved in metanephros formation. Most genes were found to be expressed in homologous locations in the mesonephros and the metanephros. These include the transcription factors Osr1, Eya1 and Pax2 (referred as undifferentiated markers); the transcription factor Lim1 and the signaling molecule Wnt4 (referred as differentiated markers). In order to investigate the role of the duct in regulating mesonephros differentiation, a blockage was inserted aimed to prevent caudal duct migration and by that, preventing interactions between the duct and mesonephric tissue. We have found that the duct is not required for activation or maintenance of early mesonephric undifferentiated markers, but is required for expression of differentiated markers and initiation of tubular differentiation. Activation of ectopic Wnt signaling (expressed in the duct) posterior to the duct-block was partially able to rescue the expression of Lim1 and Wnt4.
Utilizing an in-vitro explant assay, we found that the developmental potential of mesonephric mesenchymal tissue differs along the anterior-posterior axis. Explants generated from more anterior mesodermal tissue (i.e. developmentally more mature) exhibited duct and tubule formation, in contrast to posterior explants. Ectopic activation of Wnt signaling did not induce tubulogenesis in posterior explants nor did it increase differentiation among anterior explants. Explants obtained from the blocked side of the embryo, which did not contained a duct, were also not affected by Wnt signaling and spontaneous differentiation was observed in anterior, ‘duct-free’ explants.
Based on our results, we conclude that proper mesonephros formation requires duct signals in addition to Wnt and also requires maturation of the mesonephric mesenchyme to become competent to respond to these signals.