KUSAKABE, R; TOCHINAI, S; KURATANI, S; RIKEN Center for Developmental Biology, Japan; Grad. Sch. of Sci., Dept. of Biol.Sci., Hokkaido Univ., Japan; RIKEN Center for Developmental Biology, Japan: Analysis of Expression of Foreign Genes Introduced into Embryos of the Lamprey, Lampetra japonica: a New Technique to Analyze Evolutionary Changes in Gene Regulation.

The lamprey occupies a crucial position of phylogeny for the study of vertebrate evolution. To investigate the cross-species compatibility of 5� upstream regulatory regions, we introduced exogenous gene constructs into fertilized eggs of the Japanese lamprey, Lampetra japonica. Eggs were injected with gene constructs in which coding sequences of reporter genes such as LacZ or GFP had been connected to either virus promoters or 5′ regulatory regions of gnathostome actin genes. Reporter gene expression was recorded from two days of incubation for more than a month. Expression patterns were highly mosaic and differed among individuals. Strikingly, GFP was expressed specifically in striated muscle in lamprey embryos when driven by 5� upstream regions of medaka Olyzias latipes muscle actin genes. This implies that a part of muscle-specific gene regulatory mechanism may have existed in the common ancester of vertebrates. Tissue-restricted expression of these reporter genes has been also achieved by applying electric pulses immediately after microinjection of gene constructs into the targeted tissue of the embryo. Some of the labeled cells were traced throughout their migration and differentiation. These techniques potentially facilitate detailed cell lineage analyses of lamprey embryos. Another important application would be to introduce developmental genes of the lamprey or other animals into lamprey embryos, which would provide us with information on evolutionary changes in functions of genes or gene cascades.