A linear fragment of the pRK3lacZ plasmid (RSVlacZ) and circular DNA o
f pCMVlacZ were injected into rabbit zygotes. The embryos were culture
d for 24-72 h and analyzed with chromogenic X-gal substrate for bacter
ial beta-galactosidase. The expression of RSVlacZ DNA was revealed in
6-16-cell embryos, The expression of pCMVlacZ plasmid was low in 2-bla
stomere embryos, and high in 4-16-cell embryos. In both cases, no beta
-galactosidase activity was observed in one-cell embryos. The results
obtained indirectly suggest selective and stepwise gene activation in
the course of rabbit embryo development.