PROVIRAL INACTIVATION OF THE NPAT GENE OF MPV-20 MICE RESULTS IN EARLY EMBRYONIC ARREST

The Mpv 20 transgenic mouse strain Nas created by infection of embryos with a defective retrovirus, When Mpv 20 heterozygous animals were cr ossed, no homozygous neonatal mice or midgestation embryos were identi fied, When embryos from heterozygous crosses were cultured in vitro, a pproximately one quarter arrested as uncompacted eight-fell embryos, i ndicating that proviral insertion resulted in a recessive lethal defec t whose phenotype was manifest very early in development. Molecular cl oning of the Mpv 20 insertion site revealed that the provirus had disr upted the Npat gene, a gene of unknown function, resulting in the prod uction of a truncated Npat mRNA, Expression of the closely linked Aim gene was found to he unaffected by the provirus.