GEOapplication/xmlftp://ftp.ncbi.nlm.nih.gov/geo/series/GSE328nnn/GSE328965/primaryOK200TranscriptomicsAmbystoma mexicanumExpression profiling by high throughput sequencinghttps://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE328965GEOGSEfalseConserved anterior/posterior tissue asymmetry encodes proximal/distal positional information during axolotl limb regenerationThe ability of mammals to regenerate missing limb structures is limited to the distal fingertip. In contrast, axolotls can regenerate entire limbs, offering a powerful model to uncover conserved patterning mechanisms. Axolotl limb regeneration requires the active deployment of molecular signaling pathways that re-create the anterior-posterior (A/P) axis. However, how A/P patterning is modulated across limb segments, and whether similar mechanisms operate in mammals, remains unclear. To address this, we performed spatial transcriptomic analyses on regenerating axolotl limbs using a newly developed SpatialFlux package. Interestingly, we found that A/P genes were expressed in an asymmetric fashion along the limbs proximal/distal (Pr/Di) axis in uninjured and regenerating axolotl limb tissues. This asymmetric A/P boundary aligns with the expression of AP-1 complex components and ERK signaling activation previously shown to be distally enriched in developing embryonic limb buds. Treatment of blastemas in different limb positions with an ERK inhibitor shows that ERK signaling is an upstream modulator of both distal and posterior limb patterning genes, linking the asymmetric A/P boundary with the Pr/Di positioning of the blastema along the limb axis. These findings challenge the long-standing model of a symmetrical A/P midline boundary in limbs, offering clarity to findings that previously were incongruent with the midline boundary model. Here, we propose a revised asymmetric boundary model, in which shifting A/P ratios regulates Pr/Di patterning. Remarkably, this same pattern is observed in fetal human limbs, revealing a new, evolutionarily conserved paradigm for developmental and regenerative limb patterning.2026/06/18GSE328965GSM9694999GSM9695007GSM9695006GSM9695009GSM9695008GSM9695014GSM9695003GSM9695013GSM9695002GSM9695005GSM9695015GSM9695004GSM9695010GSM9695012GSM9695001GSM9695000GSM969501136488328965Ambystoma mexicanum