The planarian wound epidermis gene equinox is required for blastema formation in regeneration

<jats:title>Abstract</jats:title><jats:p>Regeneration often involves the formation of a blastema, an outgrowth or regenerative bud formed at the plane of injury where missing tissues are produced. The mechanisms that trigger blastema formation are therefore fundamental for regeneration. Here, we identify a gene, which we named <jats:italic>equinox</jats:italic>, that is expressed within hours of injury in the planarian wound epidermis. <jats:italic>equinox</jats:italic> encodes a predicted secreted protein that is conserved in many animal phyla. Following <jats:italic>equinox</jats:italic> 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 <jats:italic>equinox</jats:italic>, to regeneration of positional information and blastema formation, indicating a broad regulatory role of the wound epidermis in diverse regenerative contexts.</jats:p>