Gene Transfer in Living Organisms
Oocytes and eggs of Xenopus laevis are valuable tools for testing the activity of biological macromolecules. Oocytes have been injected with protein (reviewed by Lane 1981), RNA (Gurdon et al. 1974; Woodland and Wilt 1980a), and DNA (reviewed by Gurdon and Melton 1981) molecules. The unfertilized egg has been particularly useful in studying the replication of injected DNA (Harland and Laskey 1980; Hines and Benbow 1982). mRNA (Woodland and Wilt 1980b) and genomic DNA (Gurdon and Brown 1977) injected into fertilized eggs is maintained in the active state for a while, but seems to disappear in later developmental stages. Only with the advent of DNA cloning techniques has it become possible to inject defined protein-coding genes into the fertilized frog egg and to study their fate throughout development. To this end, cloned genes coding for the rabbit β-globin gene (Rusconi and Schaffner 1981) and for sea urchin histone genes (Bending 1981) were used in our laboratory. Both kinds of gene were replicated as extrachromosomal circles within developing Xenopus embryos, and were correctly transcribed around blastula-gastrula stage. Whereas most injected DNA was degraded after gastrula stage, a low number of rabbit β-globin genes became stably associated with the Xenopus genome and persisted throughout metamorphosis. In the present chapter we take a closer look at the state of such injected DNA sequences.
KeywordsXenopus Laevis Globin Gene Thymidine Kinase Promoter HpaII Site SV40 Enhancer
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