Figure 3. Evolution and functional role of Mlpt/Tal/Pri in arthropods. Several arthropods display an ortholog of Mlpt/Tal/Pri (original alignments and phylogenetic trees from Galindo et al., 2007 and Savard et al., 2006). In the short-germ embryo of the beetle Tribolium castaneum, mlpt was shown to be expressed in the legs and trachea, where it acts as a gap gene during embryogenesis (Savard et al., 2006). In the long-germ embryo of the fly Drosophila melanogaster, Mlpt/Tal/Pri was shown to be involved in several processes, which are displayed in red (Chanut-Delalande et al., 2014; Galindo et al., 2007; Kondo et al., 2007, 2010; Pueyo and Couso, 2008, 2011). Notch, Svb and EcR are the known regulators of Mlpt/Tal/Pri (Chanut-Delalande et al., 2014). Three unknown aspects of the evolution of Mlpt/Tal/Pri are highlighted in blue. These include the origin of the gene in arthropods, its ancestral function, and the loss of gap gene function after the split between the common ancestor of Coleoptera and Diptera. It is also possible that the gap gene function of Mlpt/Tal/Pri was independently acquired in Coleoptera.