Fig. 2. Nr6a1 is required for trunk elongation and timely activation of sacro-caudal identity.

A Skeletal preparation of E18.5 embryos following conditional deletion of Nr6a1 revealed a dose-dependent reduction in the number of thoraco-lumbar elements. The number of biologically independent samples assessed: Nr6a1^+/+ n = 8; Nr6a1^+/− n = 10; Nr6a1^−/− n = 14. B In WT skeletons, removal of pelvic bones allowed visualisation of transverse process morphology characteristic of lumbar (L) and sacral (blue S) elements. In two representative TCre^ERT2;Nr6a1^flx/flx embryos, positioning of the normal sacral region is defined by the presence of rudimentary pelvic bones (blue S) and lumbar elements that have assumed sacral identity marked (red S). Red asterisk indicates lateral fusions between two adjacent elements. LHS = left-hand side; RHS = right-hand side. C Quantification of thoraco-lumbar and sacro-caudal vertebral number following conditional deletion of Nr6a1 alleles. Raw data is presented in the upper plots. Mean differences relative to wildtype (+/+) are presented in the lower plots as bootstrap sampling distributions. The mean difference for each genotype is depicted as a black dot and 95% confidence interval is indicated by the ends of the vertical error bar. D Whole mount in situ hybridisation for Hoxd11 in E10.5 embryos revealed a rostral shift in the anterior limit of expression in TCre^ERT2;Nr6a1^flx/flx embryos compared to control. Ectopic Hoxd11 expression in TCre^ERT2;Nr6a1^flx/flx embryos is marked with a red line in lateral view. In dorsal view, the normal anterior limit is marked with a red dotted line, with ectopic Hoxd11 expression restricted to the paraxial mesoderm. Consistent spatial changes were observed in 3 biologically independent samples/genotype.