Gtl2lacZ, an insertional mutation on mouse chromosome 12 with parental origin-dependent phenotype

We have produced a transgenic mouse line, Gtl2lacZ (Gene trap locus 2), that carries an insertional mutation with a dominant modified pattern of inheritance:heterozygous Gtl2lacZ mice that inherited the transgene from the father show a proportionate dwarfism phenotype, whereas the penetrance and expressivity of the phenotype is strongly reduced in Gtl2lacZ mice that inherited the transgene from the mother. On a mixed genetic background this pattern of inheritance was reversible upon transmission of the transgene through the germ line of the opposite sex. On a predominantly 129/Sv genetic background, however, transgene passage through the female germ line modified the transgene effect, such that the penetrance of the mutation was drastically reduced and the phenotype was no longer obvious after subsequent male germ line transmission. Expression of the transgene, however, was neither affected by genetic background nor by parental legacy. Gtl2lacZ maps to mouse Chromosome 12 in a region that displays imprinting effects associated with maternal and paternal disomy. Our results suggest that the transgene insertion in Gtl2lacZ mice affects an endogenous gene(s) required for fetal and postnatal growth and that this gene(s) is predominantly paternally expressed.