Iroquois transcription factor irx2a is required for multiciliated and transporter cell fate decisions during zebrafish pronephros development.

The genetic regulation of nephron patterning during kidney organogenesis remains poorly understood. Nephron tubules in zebrafish are composed of segment populations that have unique absorptive and secretory roles, as well as multiciliated cells (MCCs) that govern fluid flow. Here, we report that the transcription factor iroquois 2a (irx2a) is requisite for zebrafish nephrogenesis. irx2a transcripts localized to the developing pronephros and maturing MCCs, and loss of function altered formation of two segment populations and reduced MCC number. Interestingly, irx2a deficient embryos had reduced expression of an essential MCC gene ets variant 5a (etv5a), and were rescued by etv5a overexpression, supporting the conclusion that etv5a acts downstream of irx2a to control MCC ontogeny. Finally, we found that retinoic acid (RA) signaling affects the irx2a expression domain in renal progenitors, positioning irx2a downstream of RA. In sum, this work reveals new roles for irx2a during nephrogenesis, identifying irx2a as a crucial connection between RA signaling, segmentation, and the control of etv5a mediated MCC formation. Further investigation of the genetic players involved in these events will enhance our understanding of the molecular pathways that govern renal development, which can be used help create therapeutics to treat congenital and acquired kidney diseases.