Body wall muscles in Msp300^3prime homozygous third instar larvae frequently show nuclei clustering together or in contact with each other, instead of the typically even spaced in controls.

The striated muscle in Msp-300^3prime mutant third instar larvae exhibits aggregation of the myonuclei and aberrant nuclear shape, as well as variable nuclear size. In contrast to wild to wild type, where the nuclei are tightly associated with the myofibril compartment, Msp-300^3prime mutant myonuclei are dissociated from the core acto-myosin compartment and float above it. The sarcomeric organisation of the muscles is retained.

Muscles from third instar larvae homozygous mutant for Msp-300^3prime show clustering of the mitochondria and endoplasmic reticulum.

Homozygous klar^Δ1-18 mutant larvae exhibit a 70% reduction in their motility compared to wild type.

Adult flies homozygous mutant for Msp-300^3prime are unable to fly.

Msp-300^3prime homozygotes are semi-lethal (approximately 20% of expected homozygotes survive). They do not display any obvious phenotype and move normally. Over time, the movements become slower and the larvae die before entering the second instar. There is no detectable difference in the arrangement or the movement of the body wall muscles of wild-type and mutant individuals when observing the larvae in polarised light.

Msp-300^3prime homozygous flies, in which the KASH domain coding part of the Msp-300 locus is deleted, exhibit normal eyes.

Msp-300^3prime homozygous females lay normal eggs.

Msp-300^3prime germline clones lay normal eggs, with no observable defects in nuclear position or nuclear architecture in the egg chambers.