In vivo activity of ΦC31 integrase in somatic and germ cells. A: Embryos injected with the Sox10:egfp enhancer analysis vector and mCh donor plasmid, together with RNAs encoding Tol2 transposase and ΦC31o integrase, show mCh+ cells in the same tissues as the GFP+ cells seen with injection of the analysis vector alone. Fluorescently labeled cells are detected in tissues that are typically positive using the Sox10 enhancer, including the oligodendrocytes of the spinal cord (arrowheads) and glia associated with the lateral line nerve (arrow). B–D: Embryos carrying an integrated egfp transgene with an enhancer from the ACAN gene (C) were injected with the donor plasmid and ΦC31o RNA. Injected embryos display mCh+ cells overlapping the Aggrecan pattern of expression in the notochord at 1 dpf (B), demonstrating appropriate recombination in somatic cells. E–L: ΦC31o mediates recombination in germ cell precursors. Embryos carrying the integrated Sox10:egfp transgene were injected with the mCh targeting plasmid and ΦC31o RNA, and the resulting fish raised to adulthood. In the progeny of some injected fish, mCh expression (F) replaced the specific egfp expression pattern (G), indicative of RMCE in germ cells of the injected fish. Fish carrying an integrated transgene with an enhancer from TWIST1 were similarly injected with targeting plasmid and ΦC31o RNA; from one founder, embryos with mCh expression in the complete pattern were obtained (J), as well as progeny with the original egfp expression (K).