The dorsal–ventral axis regulates planarian blastema formation and patterning
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maybrun-cmaybrun-phd-biology-2026-thesis .pdf
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Author(s)
Maybrun, Chloe L.
Advisor(s)
Reddien, Peter W.
Date Issued
February 2026
Publisher
Massachusetts Institute of Technology
Abstract
Regeneration often involves the formation of a blastema, an outgrowth at the plane of injury where missing tissues are produced. The mechanisms that trigger blastema formation and promote blastema patterning are therefore fundamental for regeneration. Here, we identify a gene, which we named equinox, that is expressed within hours of injury in the planarian wound epidermis. equinox encodes a predicted secreted protein that is conserved in many animal phyla. Following equinox inhibition, amputated planarians fail to maintain wound-induced gene expression and to subsequently undergo blastema outgrowth. Associated with these defects is an inability to reestablish lost positional information needed for missing tissue specification. Our findings link the planarian wound epidermis, through equinox, to regeneration initiation, indicating a broad regulatory role of the wound epidermis in diverse regenerative contexts.
The coordination of patterning across orthogonal tissue axes in the blastema is likely important for proper regeneration. Patterns in the blastema must additionally be integrated with axis patterns present in the regenerating fragment. Planarian adult axis patterning serves as a robust context for uncovering mechanisms of such pattern integration. Here, we demonstrate a regulatory role of the dorsal–ventral boundary (DVB) in coordinating pattern formation on the dorsal–ventral (DV) and anterior–posterior (AP) axes. Wnt inhibition results in anterior positional information induction and ectopic head formation that is restricted to the DVB. DVB can be transplanted, and DVB identity can be experimentally induced at ectopic locations. Ectopic DVB is competent for anterior positional identity induction following Wnt inhibition, enabling the generation of animals with ectopic heads at experimentally dictated locations. DVB removal blocks anteriorization caused by Wnt inhibition and prevents anterior positional information expression during head regeneration. Anterior positional information induction at the DVB after Wnt inhibition occurs independently from anterior pole formation, which promotes head patterning in regeneration. Our findings reveal a hierarchical model of pattern integration across body axes in which DV patterning is central by producing a DVB with competence to direct formation of large AP axis regions. This mechanism enables coordination of orthogonal positional information in the context of regeneration.
MIT Department
Massachusetts Institute of Technology. Department of Biology
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