7. Except for studies where gene function has been inhibited by the expression of dominant negative mutations (29-31) or maternal mRNAs where degraded following injection with oligonucleotides (12-15), it has been difficult to inhibit the function of genes in the early embryo specifically. In the future, we also hope to combine transgenesis with antisense (32-34) and ribozyme (35-37) technologies in order to deplete specific gene products from Xenopus embryos.
The advantages of the frog system are numerous, but one major disadvantage is that it has not been exploited at the genetic level. The method for transgenesis we have developed can be adopted for an insertional mutagenesis scheme. Since Xenopus laevis is pseudotetraploid and has a long generation time, we suggest using Xenopus tropicalis, which is diploid and has a generation time of around 46 mo (38). For similar reasons, Xenopus tropicalis will also be the species of choice for doing targeted mutations.
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