The Role of isthmin-1 in metanephric mesenchyme condensation and ureteric bud branching morphogenesis

Abstract

Kidney development is a complex process involving highly regulated reciprocal interactions between epithelial and mesenchymal tissues. Isthmin-1 (Ism1) is a 60-kDa secretory protein first identified in the isthmus region in Xenopus. During murine kidney development, Ism1 is expressed in metanephric mesenchyme (MM) and ureteric bud (UB). Mouse embryos with Ism1 knockout exhibit various degrees of renal agenesis. The MM condensation as well as the first branching morphogenesis event at E11.5 fail to occur in the mutant kidneys. This study seeks to unravel the cellular processes and molecular mechanisms involved in regulation of kidney development by Ism1. Exogenous Ism1 upregulates cell adhesion molecules, consolidating the important role of Ism1 in MM condensation. Besides, this work also establishes the association between Ism1 and Ret signalling, a major pathway that promotes UB outgrowth and branching. Findings in the immunoprecipitation experiments suggest that Ism1 interacts with Gdnf and the extracellular domain of Gfrα1, a co-receptor of Gdnf. Exogenous Ism1 and Gdnf can promote in vitro tubulogenesis, further delineating their effects on UB growth and branching. To gain more insights into the role of Ism1 in UB and MM, Ism1 knockout cell lines were generated by CRISPR/Cas9 gene editing. Recombination co-culture in 3D gel matrix further demonstrates the importance of Ism1 in both UB and MM. Taken together, this study uncovers the possible molecular mechanisms and biological functions of Ism1 in kidney branching morphogenesis in early development. More work is required to pinpoint the exact molecular mechanism by which Ism1 regulates Gdnf/Ret signalling.