Failure of digit tip regeneration in the absence of Lmx1b suggests Lmx1b functions disparate from dorsoventral polarity

Mammalian digit tip regeneration is linked to the presence of nail tissue, but a nail-explicit model is missing. Here, we report that nail-less double-ventral digits of ΔLARM1/2 mutants that lack limb-specific Lmx1b enhancers, fail to regenerate. To separate the nail’s effect from the lack of DV polarity, we also interrogate double-dorsal double-nail digits and show that they regenerate. Thus, DV polarity is not a prerequisite for regeneration and the nail requirement is supported. Transcriptomic comparison between wild-type and non-regenerative ΔLARM1/2 mutant blastemas reveals differential up-regulation of vascularization and connective tissue functional signatures in wild-type versus upregulation of inflammation in the mutant. These results, together with the finding of Lmx1b expression in the postnatal dorsal dermis underneath the nail and uniformly in the regenerative blastema opens the possibility of additional Lmx1b roles in the progression of digit tip regeneration, in addition to the indirect effect of mediating the formation of the nail. RNA-seq from dissected blastema from amputated digit tips; stage: 12 or 14 days post amputation (dpa); mouse genotype: Wildtype (2 biological replicates) or ΔLARM1/2 (3 biological replicates)