Figure 1.

Schematic representation of the gene trap retrovirus and the method for morphology-based screening. The gene trap retrovirus contains a SA and IRES upstream of the puromycin resistance and β-geo genes. Productive integration occurs in an intron of an expressed gene downstream of coding exons such that the puromycin resistance gene is spliced into the gene transcript. After selection with G418 and puromycin, the mutant clones were morphologically examined under a fluorescent microscope. The abnormal phenotype should be reverted to normal through Cre-mediated excision if the phenotype is due to the provirus insertion.