Comparative Studies of Renin-Null Zebrafish and Mice Provide New Functional Insights.

Background: The renin-angiotensin system is highly conserved across vertebrates, including zebrafish, which possess orthologous genes coding for renin-angiotensin system proteins, and specialized mural cells of the kidney arterioles, capable of synthesising and secreting renin.
Methods: We generated zebrafish with CRISPR-Cas9-targeted knockout of renin ( ren ^-/- ) to investigate renin function in a low blood pressure environment. We used single-cell (10×) RNA sequencing analysis to compare the transcriptome profiles of renin lineage cells from mesonephric kidneys of ren ^-/- with ren ^+/+ zebrafish and with the metanephric kidneys of Ren1 ^{c -/-} and Ren1 ^{c +/+} mice.
Results: The ren ^-/- larvae exhibited delays in larval growth, glomerular fusion and appearance of a swim bladder, but were viable and withstood low salinity during early larval stages. Optogenetic ablation of renin-expressing cells, located at the anterior mesenteric artery of 3-day-old larvae, caused a loss of tone, due to diminished contractility. The ren ^-/- mesonephric kidney exhibited vacuolated cells in the proximal tubule, which were also observed in Ren1 ^{c -/-} mouse kidney. Fluorescent reporters for renin and smooth muscle actin ( Tg(ren:LifeAct-RFP; acta2:EGFP )), revealed a dramatic recruitment of renin lineage cells along the renal vasculature of adult ren ^-/- fish, suggesting a continued requirement for renin, in the absence of detectable angiotensin metabolites, as seen in the Ren1 YFP Ren1 ^{c -/-} mouse. Both phenotypes were rescued by alleles lacking the potential for glycosylation at exon 2, suggesting that glycosylation is not essential for normal physiological function.
Conclusions: Phenotypic similarities and transcriptional variations between mouse and zebrafish renin knockouts suggests evolution of renin cell function with terrestrial survival.