Six2 paralogs are required for proximal tubule development in the Zebrafish pronephros

Abstract

The mammalian metanephric kidney develops from reciprocal interactions between the metanephric mesenchyme and ureteric bud (UB) to give rise to a variety of cell types and structures including interstitial cells, vasculature, and epithelial tubules. Progenitor cells adjacent to the UB, termed cap mesenchyme (CM), undergo mesenchymal‐to‐epithelial transition (MET) to form epithelial structures called renal vesicles before elongating and differentiating into nephrons, the functional unit of the kidney. Several genes are expressed in the CM that are required for proper kidney development. One gene encodes the transcription factor Six2, which is known to play a role in self‐renewal of the CM and is turned off in differentiated nephron epithelium. Loss of Six2 in mammals results in renal hypodysplasia due to premature loss of CM. However, Six2 expression persists as cells undergo MET from the CM to form renal vesicles, a structural precursor to differentiated nephrons. Currently, it is not known what role Six2 may play in the differentiation program required to form new nephron epithelium. The zebrafish embryonic pronephros shares features with mammalian nephrons including a similar developmental genetic program and conserved segmentation of the epithelial tubule. Unlike mammals however, the zebrafish pronephros develops directly from the intermediate mesoderm without the need for a continuous population of progenitor cells. This allows the functional study of genes which play a role in CM self‐renewal but also may have roles in cellular differentiation during nephron development. Here we have cloned and characterized the zebrafish Six2 homologs during pronephric development. The zebrafish six2a and six2b genes show conserved expression in the intermediate mesoderm, although with slight differences between the two paralogs. Gene knock‐down, by injection of specific anti‐sense morpholino oligonucleotides (MO) results in kidney cysts and aberrant expression of glomerular and proximal tubule markers, such as wt1a and slc20a1a. Interestingly, distal segments remain intact suggesting Six2 plays a role in cell differentiation of proximal elements of the pronephric nephron.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.