mus309N1/mus309D2 mus312D1/mus312Z1973 double mutant larvae have small brains, lack imaginal discs and have a reduced number of salivary gland imaginal ring cells. The nuclei of the remaining salivary gland imaginal ring cells appear larger than normal. Mitotic neuroblasts in these larvae show extreme genome instability; no mitotic nuclei with completely intact chromosomes are detected and approximately one-third show polyploidy.
The addition of spn-Aunspecified suppresses the the chromosome breakage and polyploidy phenotypes seen in mitotic neuroblasts of mus309N1/mus309D2 mus312D1/mus312Z1973 larvae, and also suppresses the defects in the salivary gland imaginal ring cells seen in the mus309N1/mus309D2 mus312D1/mus312Z1973 double mutants. However, addition of spn-Aunspecified does not suppress the pupal lethality, small brains and lack of imaginal discs seen in the mus309N1/mus309D2 mus312D1/mus312Z1973 double mutants.
mus312D1/mus312Z1973, mus309D2/mus309N1 double mutants are inviable, dying after pupariation. Third-instar larvae have melanotic tumors and lack larval imaginal discs. Larval brains of double mutants are greatly reduced in size.