Deletion of Pax1 scoliosis-associated regulatory elements lead to a female-biased tail abnormality

Adolescent idiopathic scoliosis (AIS) is sexually dimorphic, with increased incidence in females. A GWAS identified a female-specific AIS susceptibility locus near the PAX1 gene. Here, we used mouse enhancer assays, three mouse enhancer knockouts and subsequent phenotypic analyses to characterize this region, finding it to cause a sexually dimorphic kinky tail phenotype. Using mouse enhancer assays, we characterized a sequence, PEC7, that overlaps the AIS-associated variant to be active in the tail tip and intervertebral disc.[RS1] Removals of PEC7 and a known sclerotome enhancer nearby (Xe1), and deletion of both sequences led to a kinky phenotype only in the Xe1 and combined (Xe1+PEC7) knockouts, with only the latter showing a female sex dimorphic phenotype. Extensive phenotypic characterization of these mouse lines implicated several differentially expressed genes and estrogen signaling in the sex dimorphic bias. In summary, our work functionally characterizes an AIS-associated locus and dissects the mechanism for its sexual dimorphism.