mesenchymal to epithelial transition involved in metanephric renal vesicle formation

Definition

Target type: biologicalprocess

A transition where a mesenchymal cell establishes apical/basolateral polarity,forms intercellular adhesive junctions, synthesizes basement membrane components and becomes an epithelial cell that will contribute to the shaping of the metanephric renal vesicle. [GOC:mtg_kidney_jan10]

Metanephric renal vesicle formation involves a complex process of mesenchymal to epithelial transition (MET). This transition is critical for the development of the nephron, the functional unit of the kidney. Here's a detailed description:

1. **Mesenchymal Cells:** The process begins with mesenchymal cells, undifferentiated cells that are derived from the metanephric mesenchyme. These cells have a loose, fibroblast-like morphology and express specific markers such as Pax2 and Wnt4.

2. **Induction by the Ureteric Bud:** The ureteric bud, an outgrowth from the Wolffian duct, interacts with the metanephric mesenchyme, triggering the MET process. This interaction is mediated by reciprocal signaling pathways, including GDNF (glial cell line-derived neurotrophic factor) from the mesenchyme and RET (receptor tyrosine kinase) from the ureteric bud.

3. **Epithelial Commitment and Cell Aggregation:** The inductive signals from the ureteric bud initiate a cascade of events that cause mesenchymal cells to commit to an epithelial fate. They begin to express epithelial markers like E-cadherin and ZO-1, and their morphology changes from fibroblast-like to rounded, epithelial-like cells. These cells then aggregate around the tips of the ureteric bud branches, forming epithelial spheres known as renal vesicles.

4. **Polarization and Lumen Formation:** As the renal vesicles form, the epithelial cells undergo polarization. The apical surfaces of the cells face the lumen of the vesicle, while the basolateral surfaces face the surrounding mesenchyme. This polarization is crucial for the formation of a functional lumen within the vesicle.

5. **Differentiation and Nephron Development:** The renal vesicles further differentiate into various segments of the nephron, including the glomerulus, proximal tubule, loop of Henle, and distal tubule. This differentiation involves the expression of specific genes and the formation of specialized cell types within the nephron.

The mesenchymal to epithelial transition during metanephric renal vesicle formation is a tightly regulated process involving complex signaling pathways, transcription factors, and cell-cell interactions. It is essential for the proper development of the kidney and its ability to filter blood and produce urine.'
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