A 2.8 kb segment including exons 1, 2 and part of exon 3 was replaced with a neo cassette via homologous recombination. Northern blot analysis confirmed the absence of RNA expression in homozygotes. A subsequent publication demonstrated that the neo cassette also replaced the first exon of the neighboring gene, Mettl23, located on the opposite strand. RT-PCR confirmed absence of Mettl23 mRNA in homozygous embryos. (J:90288, J:137989)