Meeting Abstract
The CRAL-TRIO domain is a structural region common to proteins that transport hydrophobic tocopherols. In vertebrates (CRALBP) and Drosophila (PINTA) CRAL-TRIO domain containing proteins transport vitamin A-derived chromophores that are necessary for vision. Members of the CRAL-TRIO domain gene family have undergone lineage-specific duplications in insects, and an expansion in Lepidoptera. Lepidopterans have twice as many CRAL-TRIO domain genes compared to other insects. However, there is no lepidopteran ortholog of pinta. We aimed to 1) characterize the molecular evolution of the CRAL-TRIO domain gene family and to 2) identify a candidate gene for chromophore transport in butterflies. By searching a de novo transcriptome and reference genome, we found 43 CRAL-TRIO domain genes in a butterfly species, Heliconius melpomene. A phylogeny revealed two duplication events and an expansion of these genes in H. melpomene. 36 of the CRAL-TRIO domain genes were located in tandem on 3 chromosomes. We used 18 resequenced genomes from 4 subspecies to detect copy number variation of 32 CRAL-TRIO domain genes. We also performed differential expression analysis using RNA-Seq from the heads, antennae, legs and mouthparts of H. melpomene to identify a candidate CRAL-TRIO domain gene, Hme CTD31, upregulated in heads. RT-PCR confirmed that Hme CTD31 is expressed in the retina rather than the brain. Furthermore, immunohistochemistry showed that the Hme CTD31 protein is found in primary and secondary pigment cells. The CRAL-TRIO domain gene family is likely evolving by tandem duplications and a member of this family potentially functions in butterfly visual pigment transport.
