Further analysis on the male-specific lethal mutations that affect dosage compensation in Drosophila melanogaster.

The male-specific lethal genes (msl) of D. melanogaster represent a set of genes whose functions are required for the specific X chromosome hypertranscription in males (dosage compensation). We have carried out the clonal analysis of one of those msl mutations: msl-3 b. Clones homozygous for msl-3 b are deleterious; this mutation presents cell autonomy and in the cases where msl clones appeared in sexually dimorphic regions (5th and 6th tergites) they do not show sexual transformation. Moreover, the lethal phase and the growth dynamics (measured by the protein content during larval growth) are the same for male larvae homozygous for one msl mutation (msl-1) or three msl mutations (msl-2 msl-1 mle), i.e. the msl mutations do not show additive effects. This paper considers the possible interactions between the msl genes that bring about dosage compensation.