Nuclear receptor NR4A is required for patterning at the ends of the planarian anterior-posterior axis.

Abstract

Positional information is fundamental to animal regeneration and tissue turnover. In planarians, muscle cells express signaling molecules to promote positional identity. At the ends of the anterior-posterior (AP) axis, positional identity is determined by anterior and posterior poles, which are putative organizers. We identified a gene, <i>nr4A</i>, that is required for anterior- and posterior-pole localization to axis extremes. <i>nr4A</i> encodes a nuclear receptor expressed predominantly in planarian muscle, including strongly at AP-axis ends and the poles. <i>nr4A</i> RNAi causes patterning gene expression domains to retract from head and tail tips, and ectopic anterior and posterior anatomy (e.g., eyes) to iteratively appear more internally. Our study reveals a novel patterning phenotype, in which pattern-organizing cells (poles) shift from their normal locations (axis extremes), triggering abnormal tissue pattern that fails to reach equilibrium. We propose that <i>nr4A</i> promotes pattern at planarian AP axis ends through restriction of patterning gene expression domains.