ABSTRACT
The South African clawed frog, Xenopus laevis, has been used as a model system for the research of developmental biology for many decades. Undoubtedly, the large size of the amphibian oocytes makes for easy manipulation of individual cells. Upon fertilization, rapid development of these large (~1 mm diameter) cells allows for easy visualization of cleavage events and vertebrate development. Furthermore, these animals require low maintenance, are inexpensive and easy to care for, and most importantly give rise to large numbers of oocytes and eggs. While using the X. laevis model system clearly has its advantages, there are shortcomings, notably the animal’s long breeding cycle and tetraploidy. In fact, these disadvantages have in the past made loss-of-function studies such as gene knockouts difficult and complicated. With the discovery that the X. laevis oocyte can translate microinjected mRNA (Gurdon and Lane, 1971), came the advent of overexpression studies, and early forms of loss-of-function methods such as the use of antisense RNA or dominant negative mRNA. These techniques, however, have their caveats as well; a high concentration of antisense RNA is necessary for this approach to work accordingly and the outcome is often transient (Dirks et al., 2003) and non-specific (Zhou et al., 2002).
