Insertion at nucleotide 2R:6046076 (release 5 coordinates), within a region common to the 5' UTR of all three mlt isoforms.
Individualisation complexes assembled around spermatid nuclear bundles are intact in mltEY02157/mlt4210 testes, but progressed individualisation complexes (those no longer co-localising with the nuclear bundle) are often disrupted, having one or more investment cones out of register. Sleeves of F-actin associated with highly condensed spermatid bundles at the most basal end of the testis tubule are sometimes seen.
Mutants show male sterility, with highly elongated, immobile, blebbed sperm tails and altered individualisation complexes. Individualisation complexes form normally but degrade as they proceed caudally along the cyst.
Mutation is revertible on introduction of P{Δ2-3}.
Although the P{lacW}mlt4210 insertion maps within both 5'UTR of the CG12214 annotation and an intron of KCNQ (nested genes, CG12214 is entirely within a large intron of KCNQ), complementation analysis indicates that the "mlt" mutant phenotype caused by this insertion (spermatid individualisation defects) is due to an effect on CG12214 and not on KCNQ.