Simple generation of hairless mice for in vivo imaging Simple generation of hairless mice for <i>in vivo</i> imaging

The in vivo imaging of mice makes it possible to analyze disease progress non-invasively through reporter gene expression. As the removal of hair improves the accuracy of in vivo imaging, gene-modified mice with a reporter gene are often crossed with Hos:HR-1 mutant mice homozygous for the spontaneous Hrhr mutation that exhibit a hair loss phenotype. However, it is time consuming to produce mice carrying both the reporter gene and mutant Hrhr gene by mating. In addition, there is a risk that genetic background of the gene-modified mice would be altered by mating. To resolve these issues, we established a simple method to generate hairless mice maintaining the original genetic background by CRISPR technology. First, we constructed the pX330 vector, which targets exon 3 of Hr. This DNA vector (5 ng/µl) was microinjected into the pronuclei of C57BL/6J mice. Induced Hr gene mutations were found in many founders (76.1%) and these mutations were heritable. Next, we performed in vivo imaging using these gene-modified hairless mice. As expected, luminescent objects in their body were detected by in vivo imaging. This study clearly showed that hairless mice could be simply generated by the CRISPR/Cas9 system, and this method may be useful for in vivo imaging studies with various gene-modified mice.

<p>The <i>in vivo</i> imaging of mice makes it possible to analyze disease progress non-invasively through reporter gene expression. As the removal of hair improves the accuracy of <i>in vivo</i> imaging, gene-modified mice with a reporter gene are often crossed with Hos:HR-1 mutant mice homozygous for the spontaneous <i>Hr^hr</i> mutation that exhibit a hair loss phenotype. However, it is time consuming to produce mice carrying both the reporter gene and mutant <i>Hr^hr</i> gene by mating. In addition, there is a risk that genetic background of the gene-modified mice would be altered by mating. To resolve these issues, we established a simple method to generate hairless mice maintaining the original genetic background by CRISPR technology. First, we constructed the <i>pX330</i> vector, which targets exon 3 of <i>Hr</i>. This DNA vector (5 ng/<i>µ</i>l) was microinjected into the pronuclei of C57BL/6J mice. Induced <i>Hr</i> gene mutations were found in many founders (76.1%) and these mutations were heritable. Next, we performed <i>in vivo</i> imaging using these gene-modified hairless mice. As expected, luminescent objects in their body were detected by <i>in vivo</i> imaging. This study clearly showed that hairless mice could be simply generated by the CRISPR/Cas9 system, and this method may be useful for <i>in vivo</i> imaging studies with various gene-modified mice.</p>