THE ROLE OF THE PATERNAL GENOME IN THE DEVELOPMENT OF THE MOUSE GERM-LINE

The mouse germ line originates at 6.5 days post coitum (dpc) in the pr oximal epiblast, apparently in response to signals from the primitive endoderm or the extraembryonic mesoderm [1,2]. Some studies have impli ed a significant role for imprinted genes in germline development [3,4 ]. These genes, whose expression is determined by their parental origi n [5], serve complementary functions during mammalian development [6-9 ] and exert striking reciprocal phenotypic effects on androgenetic (AG : two paternal genomes) and parthenogenetic (GG/PG: two maternal genom es) cells [3,4,10], This may include a fundamental effect on germ cell development because PG but not AG cells can differentiate into viable gametes [3,4,11], suggesting that the maternal genome is obligatory f or development of the mammalian germ line. Here we show unequivocally that AG cells can differentiate into germ cells, and that in chimeras with normal cells they produce functional sperm. These studies establi sh that the paternal and maternal genomes can individually provide bot h the signal and the response required for the specification of germ c ells in mammals.