Using sperm as a vehicle for delivering exogenous DNA into an egg is an interesting potential application for ICSI in the field of animal transgenesis and biotechnology. The ability of sperm to take up and bind exogenous DNA and then transfer it into an egg during fertilization was first described 30 years ago (Brackett et al. 1971) and was rediscovered in 1989 (Lavitrano et al. 1989). Studies have shown that mouse epididymal sperm can take up 1.5-4 x 106 DNA molecules (average 5 kB). The mechanism of DNA uptake and binding of sperm relies on an ionic interaction that takes place in the subacrosomal segment of the sperm head between DNA and a group of positively charged sperm membrane proteins. Sperm-bound DNA is rapidly internalized into nuclei in 60-65% of sperm (Lavitrano et al. 1992; Francolini et al. 1993; Zani et al. 1995). While the usefulness of this method applied to sperm to be used for transgenesis by IVF remains controversial, exogenous DNA can be delivered successfully into an oocyte by coinjec-tion with sperm, suggesting an adaptable method of transgenesis (Perry et al. 1999). Clearly, further studies in this area are required to refine and improve these methods in order to establish them as a viable and reliable tool for deriving transgenic mice.
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