Conservation and Sex-Specific Splicing of the <em>transformer</em> Gene in the Calliphorids <em>Cochliomyia hominivorax</em>, <em>Cochliomyia macellaria</em> and <em>Lucilia sericata</em>

<div><p>Transformer (TRA) promotes female development in several dipteran species including the Australian sheep blowfly <em>Lucilia cuprina</em>, the Mediterranean fruit fly, housefly and <em>Drosophila melanogaster</em>. <em>tra</em> transcripts are sex-specifically spliced such that only the female form encodes full length functional protein. The presence of six predicted TRA/TRA2 binding sites in the sex-specific female intron of the <em>L. cuprina</em> gene suggested that <em>tra</em> splicing is auto-regulated as in medfly and housefly. With the aim of identifying conserved motifs that may play a role in <em>tra</em> sex-specific splicing, here we have isolated and characterized the <em>tra</em> gene from three additional blowfly species, <em>L. sericata</em>, <em>Cochliomyia hominivorax</em> and <em>C. macellaria</em>. The blowfly adult male and female transcripts differ in the choice of splice donor site in the first intron, with males using a site downstream of the site used in females. The <em>tra</em> genes all contain a single TRA/TRA2 site in the male exon and a cluster of four to five sites in the male intron. However, overall the sex-specific intron sequences are poorly conserved in closely related blowflies. The most conserved regions are around the exon/intron junctions, the 3′ end of the intron and near the cluster of TRA/TRA2 sites. We propose a model for sex specific regulation of <em>tra</em> splicing that incorporates the conserved features identified in this study. In <em>L. sericata</em> embryos, the male <em>tra</em> transcript was first detected at around the time of cellular blastoderm formation. RNAi experiments showed that <em>tra</em> is required for female development in <em>L. sericata</em> and <em>C. macellaria</em>. The isolation of the <em>tra</em> gene from the New World screwworm fly <em>C. hominivorax</em>, a major livestock pest, will facilitate the development of a “male-only” strain for genetic control programs.</p>