Larval brains of vib^RM1 mutants exhibit frequent polyploid cells but have normal frequences of anaphases, consistent with a defect in neuroblast cytokinesis.

In vib^RM1 males, early meotic telophases are completely normal and display regular actin rings and central spindles. The central spindle and the contractile ring remain normal also in most mutant mid-telophases. However, most late telophases from vib^RM1 mutants display actin rings that are not fully constricted. in approximately 11% f these late telophases, the actin rings are either discontinuous or absent and the central spindles less dense than in wild-type.

All early and mid-telophase neuroblasts from vib^RM1/Df(3R)Dl-BX12 larval brains exhibit regular central spindles and myosin rings. however, about one half of mutant neuroblasts in late telophase (approximately 48%) display poorly constricted rings.