Fig. 1. Nr6a1 expression level positively correlates with the trunk vertebral number and is regulated by known mediators of the trunk-to-tail transition.

A Nr6a1 is expressed broadly at embryonic day (E)8.5, with expression becoming progressively excluded from the posterior growth zone starting E9.5. By E10.5 Nr6a1 exhibits tissue-specific expression, followed by complete tissue clearance by E12.5. B Violin plot illustrates the Log₂ normalised count, which was derived from the raw counts from each cells divided by their size factors, of Nr6a1 in cells of the E6.5 to E8.5 mouse embryo, revealing robust expression within neuromesodermal progenitors (NMP), caudal mesoderm and caudolateral epiblast. Data derived from ref. [41]. C Expression level of Nr6a1 within the tailbud positively correlates with the number of trunk vertebrae that form later in development. Quantitative PCR analysis of Nr6a1 within tailbud tissue isolated from Gdf11 and miR-196 single and compound mutant embryos, represented as a fold change compared to wildtype (defined as 1). The number of biologically independent samples assessed: WT E9.5 n = 3, E10.5 n = 4; Gdf11^+/− E9.5 n = 3, E10.5 n = 3; miR-196a2^−/−;b^−/− E9.5 n = 3, E10.5 n = 4; Gdf11^+/−; miR-196a1^−/−;a2^−/−;b^−/− E9.5 n = 3, E10.5 n = 4; Gdf11^−/− E9.5 n = 3, E10.5 n = 2; Gdf11^−/−; miR-196a1^−/−;a2^−/−;b^−/− E9.5 n = 3, E10.5 n = 2; Error bar represents standard deviation. Source data are provided as a Source Data file. The number of additional thoraco-lumbar vertebrae observed across the allelic deletion series⁴⁴ is indicated. D Whole mount in situ hybridisation reveals that the quantitative increase of Nr6a1 in E10.5 Gdf11^−/− tailbud tissue relative to wildtype reflects a lack of timely clearance from the posterior growth zone. Consistent spatial changes were observed in 2 biologically independent samples/genotype. Red arrow indicates the neural tube.