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, nr4A, that is required for anterior- and posterior-pole localization to axis extremes. nr4A encodes a nuclear receptor expressed predominantly in planarian muscle, including strongly at AP-axis ends and the poles. nr4A 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 nr4A promotes pattern at planarian AP axis ends through restriction of patterning gene expression domains.
Highlights
Metazoans display a large diversity of developmental modes and adult forms
Using single-cell differential expression (SCDE) analysis (Kharchenko et al, 2014), we identified 198 genes with significantly higher expression (p
The planarian anterior and posterior poles have been the subjects of recent intense study because of their roles in patterning the head and tail (Reddien, 2011; Owlarn and Bartscherer, 2016; Reddien, 2018)
Summary
Metazoans display a large diversity of developmental modes and adult forms. Processes that govern the generation of form, collectively known as patterning, act to regulate cell identity, location, and number (Wolpert, 1969). RNA interference (RNAi) approaches have identified genes with regionalized expression domains that are important in AP patterning (Forsthoefel and Newmark, 2009; Adell et al, 2010; Reddien, 2011) Genes with such constitutive regionalized expression and association with pathways with planarian patterning roles are called position control genes or PCGs (Witchley et al, 2013; Scimone et al, 2016; Fincher et al, 2018). Inhibition of the FGFRL gene ndl-3 and the Wnt gene wntP-2 led to the formation of ectopic mouths and pharynges in the trunk (Lander and Petersen, 2016; Scimone et al, 2016)
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