Endothelial versus pronephron fate decision is modulated by the transcription factors Cloche/Npas4l, Tal1, and Lmo2.

Abstract

Endothelial specification is a key event during embryogenesis; however, when, and how, endothelial cells separate from other lineages is poorly understood. In zebrafish, Npas4l is indispensable for endothelial specification by inducing the expression of the transcription factor genes <i>etsrp</i>, <i>tal1</i>, and <i>lmo2</i>. We generated a knock-in reporter in zebrafish <i>npas4l</i> to visualize endothelial progenitors and their derivatives in wild-type and mutant embryos. Unexpectedly, we find that in <i>npas4l</i> mutants, <i>npas4l</i> reporter-expressing cells contribute to the pronephron tubules. Single-cell transcriptomics and live imaging of the early lateral plate mesoderm in wild-type embryos indeed reveals coexpression of endothelial and pronephron markers, a finding confirmed by creERT2-based lineage tracing. Increased contribution of <i>npas4l</i> reporter-expressing cells to pronephron tubules is also observed in <i>tal1</i> and <i>lmo2</i> mutants and is reversed in <i>npas4l</i> mutants injected with <i>tal1</i> mRNA. Together, these data reveal that Npas4l/Tal1/Lmo2 regulate the fate decision between the endothelial and pronephron lineages.