UTX expression is essential for embryonic development. (A) Schematic representation of the UTX conditional allele (UTXFD) and the conversion to the frameshifted KO allele (UTXFDC) after excision of exon 3 with Cre recombinase. (B) Western blot of littermate lysates from one UTXFDC/Y × UTXFDC/wt intercross showed efficient knockout of UTX. (C) UTX KO had no influence on the global level of the tri-methylated histone 3 lysine 27 residue (H3K27me3) relative to the histone 3 (H3) level in embryos derived from an UTXFDC/Y × UTXFDC/wt intercross. (D) Embryos isolated at different stages from UTXFDC/Y × UTXFDC/wt intercrosses. At E9.5 and E10.5, female UTXFDC/FDC embryos show growth retardation, cardiac malformations (arrowhead), and neural tube closure defects (arrow) and die between E11.5 and E13.5. A fraction of UTXFDC/Y male embryos exhibit cranioschisis at all analyzed stages. Scale bar, 1 mm.