Fibronectin (Fn1) mediates the proper organization of the Proximal Convoluted Tubule in Zebrafish Pronephros

Abstract

The zebrafish larval excretory system, the pronephros, originates from the Intermediate Mesoderm (IM) from bilateral cell progenitors. It is composed of a filtration unit, the glomerulus, and a pair of functionally and genetically segmented tubules. The Extracellular Matrix (ECM) regulates morphogenesis in several ways, by contributing to establishing polarity, being a substrate for migration, or controlling morphogen diffusion. Previous studies show that the ECM protein, Fibronectin (FN1), performs functions regulating the assembly of proximal pronephric tubules. Here we found that fibronectin is not only affecting glomerular and Proximal Convoluted Tubules (PCT) structures but also is affecting the positioning and proximal segment specification. Using Histology with Plastic resin and Whole-embryo in situ hybridization, we found that glomerulus depends on fibronectin presence for its midline fusion but not for coalescence or specification. Furthermore, we found that the PCT segment is elongated in FN1-deficient embryos, but shortened in FN1-overexpressed embryos. Our results contribute to understanding the role of ECM in the Pronehpric system showing its role in segment specification and proximal structure organization. The study provides new insights into regulation pathways that could be modulated by ECM. Further studies need to be done to evaluate the role of ECM in the distributions of factors such as Retinoic Acid and its role in segmentation, as well as the antagonism of hand2 and the interaction with osr1.