Evolution of dosage compensation in diptera: The gene maleless implements dosage compensation in Drosophila (Brachycera suborder) but its homolog in sciara (Nematocera suborder) appears to play no role in dosage compensation

In Drosophila melanogaster and in Sciara a ocellaris dosage compensation oc curs by hypertranscription of the single male X chromosome. This article re ports the cloning and characterization in S. ocellaris of the gene homologo us to maleless (mle) of D. melanogaster which implements dosage compensatio n. The Sciara mle gene produces a single transcript, encoding a helicase, w hich is present in both male and female larvae and adults and in testes and ovaries. Both Sciara and Drosophila MLE proteins are highly conserved. The affinity-purified antibody to D. melanogaster MLE recognizes the S. ocella ris MLE protein. In contrast to Drosophila polytene chromosomes, where MLE is preferentially associated with the male X chromosome, in Sciara MLE is f ound associated with all chromosomes. Anti-MLE staining of Drosophila postb lastoderm male embryos revealed a single nuclear dot, whereas Sciara male a nd female embryos present multiple intranuclear staining spots. This expres sion pattern in Sciara is also observed before blastoderm stage, when dosag e compensation is not yet set up. The affinity-purified antibodies against D. melanogaster MSL1, MSL3, and MOF proteins involved in dosage compensatio n also revealed no differences in the staining pattern between the X chromo some and the autosomes in both Sciara males and females. These results lead us to propose that different proteins in Drosophila and Sciara would imple ment dosage compensation.