His main research focus are TET enzymes, which play an important role in ES cell differentiation. Prof. Koh required a complete null Tet1 mouse line together with a reporter-exchange cassette for his research. It was not possible to achieve the full knockout by conditional targeting or by CRISPR-Cas9 deletion due to an unusually large exon 2 containing the ATG start codon with an alternative start codon in-frame at exon 4. The mouse line was generated using a knock-in strategy incorporating two reporters. The Koh group has since validated that the mouse line is Tet1 null with a consistent phenotype. Ozgene’s goGermline technology enabled Prof. Koh to obtain the key data quickly without any backcrossing or extensive validation of off-target effects.