(A) Annotation of mouse lncRNA Playrr (D030025E07Rik). e926 contains the TSS and exon 1 of Playrr and a conserved Pitx2 binding motif (asterisk). CRISPR/Cas9 mutation of e926/Playrr (PlayrrΔ926, 1420bp dashed line; PlayrrEx1sj, red and blue letters). Exon 1 (upper case), intron 1 (lower case), relative guide RNA (gRNA, light blue) and PAM motif (pink) were used to produce PlayrrEx1sj. (B) Whole mount ISH showing right-specific Playrr in WT HH21 chicken and E10.5 mouse embryos vs. bilateral Playrr expression in Pitx2-null mouse DM. (C) qRT-PCR expression in PlayrrΔ926 and PlayrrEx1sj mutants (n=3) relative to WT (n=3) of Playrr (left) and Pitx2 (right) at E10.5 or E14.5, respectively, error bars ± S.E.M. (D) Mutual antagonism of Playrr and Pitx2 expression. Scale bars in (B) 100μm. See also Figure S1 and S4.