Molecular Structure of the <i>Lmo</i> Locus

<div><p>(A) A genomic map of the <i>Lmo</i> locus. Three different first exons can be utilized, forming the basis for three alternative transcripts. Exon RA-1 is separated from the alternative start sites RB-1 and RC-1 by a large (∼30 kb) intron. <i>EP1306, EP1383,</i> and <i>pdrm</i> carry insertions 25, 73, and 91 bp, respectively, upstream of the exon RA-1 transcriptional start site. Arrows within the EP elements refer to the orientation of the insertion and the expected direction of inducible expression via UAS sites contained within the EP element. <i>Bx</i> alleles are insertions of natural transposons into the 3′ UTR of the <i>Lmo</i> gene that have been shown to stabilize <i>Lmo</i> transcript (<a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0020408#pbio-0020408-Shoresh1" target="_blank">Shoresh et al. 1998</a>). Protein-coding exons are shaded.</p> <p>(B) Expression of the <i>Lmo</i> RA transcript is enriched in <i>Drosophila</i> heads, and is reduced in the <i>EP1306</i> mutant. RNA was isolated from heads and bodies; after cDNA synthesis, quantitative RT-PCR was performed using primers specific to the RA transcript of <i>Lmo</i> in addition to primers to a reference transcript, the ribosomal protein <i>rp49</i>. Relative abundance is expressed as fold increase over control <i>(EP1631)</i> body mRNA. No detectable amplification was seen in RNase-treated controls (data not shown). Error bars represent standard error of the mean. Asterisk denotes significant difference from control (Student's paired <i>t</i>-test assuming equal variance; <i>p <</i> 0.001, <i>n</i> = 3).</p>