From the authors

Abstract

<h3>ABSTRACT</h3> Together with <i>sickle</i> (<i>skl</i>), the <i>Drosophila</i> paralogs <i>reaper</i> (<i>rpr</i>), <i>head involution defective</i> (<i>hid</i>), and <i>grim</i> (RHG) control a critical switch in the induction of programmed cell death. RHG homologs have been identified in other dipteran and lepidopteran species but not beyond. Revisiting this issue with a “taxon hopping” BLAST search strategy in current genome and transcriptome resources, I detected high confidence RHG homologs in Coleoptera (beetles), Hymenoptera (bees+wasps), Hemiptera (true bugs), termites, and cockroaches. Analyses of gene structure and protein sequence conservation revealed a shared ancestral splicing pattern and highly conserved amino acid residues at both the N- and C-terminal ends that identify <i>hid</i> as the most ancestrally organized RHG gene family member in <i>Drosophila</i>. hid-like RHG homologs were also detected in mosquitoes, redefining their <i>michelob_x</i> (<i>mx</i>) genes as an expansion of derived RHG homologs. Only singleton homologs were detected in the large majority of other insect clades. Lepidopteran RHG homologs, however, stand out by producing an evolutionarily derived splice isoform, identified in previous work, in addition to the newly detected <i>hid</i>-like isoform. Exceptional sequence diversification of select RHG homologs at the family- and genus-level explain their elusiveness in important insect genome model species like the red flour beetle <i>Tribolium castaneum</i> and the pea aphid <i>Acyrthosiphon pisum</i>. Combined, these findings expand the minimal age of the RHG gene family by about 100 million years and open new avenues for molecular cell death studies in insects.