Targeting Dosage Compensation to the X Chromosome of Drosophila Males

RNA has attracted increasing attention from biologistsbecause of its versatile talents in biological processes.RNA's capabilities are not confined just within traditional models, as messenger RNA or scaffolds of a ribosome, but have been extended to catalysis and regulationof diverse biological functions, supporting a primordial"RNA world hypothesis." One of RNA's fascinatingroles is regulation of gene expression as an RNP (ribonucleoprotein) complex. Examples include dosage compensation in Drosophila by roX RNAs, Xist/Tsix RNAs inmammalian female X-inactivation, and siRNAs/miRNAsin posttranscriptional gene regulation in various organisms. roX RNAs are required for correct targeting ofdosage compensation complexes to the Drosophila Xchromosome (Meller and Rattner 2002). We previouslyproposed that targeting occurs by spreading in cis frommultiple, discrete initiation sites (Kelley et al. 1999; Parket al. 2002; Oh et al. 2003). Here we emphasize thatspreading cannot be the sole mechanism for targeting ofdosage compensation and suggest that the MSL (Male-Specific Lethal) complex has evolved multiple ways torecognize genes on the X (Oh et al. 2004)...