LOW-LEVELS OF CHIMERISM IN RABBIT FETUSES PRODUCED FROM PREIMPLANTATION EMBRYOS MICROINJECTED WITH FETAL GONADAL CELLS

The potential pluripotency of rabbit fetal germ cells has been investi gated by using them to make chimeric embryos. Genial cells, isolated f rom enzyme-dispersed male and female transgenic fetal rabbit gonads of 18-22 days gestation, were microinjected in groups of about 10 into 6 40 nontransgenic rabbit embryos between the two-cell and expanded blas tocyst stages. Injections were made with primary isolations of genial cells, within 48 hr of their collection. The injected embryos were tra nsferred, with or without non-injected control embryos, into 49 recipi ent rabbits. Tissues from 159 resulting fetuses, implantation sites, a nd a few liveborn young were examined by PCR analysis for the two tran sgenes used (alpha-1 antitrypsin or luciferase). The overall pregnancy rate (about 80%) was not affected by the stage of development of the embryo injected, nor by co-transfer of control embryos. The survival r ate of injected embryos (18% overall, 23.6% in pregnant recipients) wa s almost identical to that of 243 control embryos. Chimerism was detec table in tissues produced from 4 of 159 (2.5%) of the injected embryos , all four of which had been injected at the 8- to 16-cell stage, This low rate of success indicates that, although passage of rabbit genial cells is not an absolute requirement for pluripotency, further invest igation should pay particular attention to improving culture condition s with a view to deriving EG cell lines, (C) 1996 Wiley-Liss, Inc.