piwi1/+ (or even more so, piwi1/piwi2) significantly partially suppresses the swollen apical tip of the testis phenotype seen in Tudor-SN0614/Tudor-SN1120 males. piwi1/piwi2 suppresses infertility seen in Tudor-SN0614/Tudor-SN1120 males. Tudor-SN0614/Tudor-SN1120 partially suppresses ovary defects in piwi1/piwi2 females.
piwi2/+ enhances the eye outgrowth phenotype phenotype of KrIf-1; approximately 7% of the progeny have an eye outgrowth phenotype in a cross of piwi2/+ females to KrIf-1/+ males. However, the reciprocal cross of KrIf-1/+ females to piwi2/+ males does not result in progeny with an eye outgrowth phenotype, indicating a maternal effect. In addition, the expression of the eye outgrowth phenotype depends on the presence of the piwi2 mutation in the progeny, indicating a zygotic effect.
Over expression of hhhs.PI in piwi2 homozygotes or heterozygotes stimulates somatic cell differentiation in ovarioles. hhhs.PI also restores germ stem cell divisions in these mutants. Rescued homozygotes often contain a full complement of germline cells. Moreover the germaria generate more egg chambers, per ovariole, similar to heterozygous controls. However fertility is not restored.