Transcriptomic, proteomic and biochemical comparison of luminescent and non-luminescent Keroplatinae larvae (Diptera: Keroplatidae).

Bioluminescence (BL) in the Keroplatinae subfamily (Diptera: Keroplatidae) is found in Keroplatus, Neoceroplatus and Orfelia fultoni larvae. In O. fultoni, BL involves an oligomeric luciferase, a luciferin called keroplatin, which is associated with a substrate binding fraction (SBF), whose molecular identity and function remain uncertain. Non-luminescent web-constructing predatory larvae of Neoditomyia sp. (Keroplatinae) also contain keroplatin and SBF in their bodies, suggesting additional unknown roles for this compound in this subfamily. To identify gene products differentially expressed between luminescent and non-luminescent larvae, especially those associated with luciferase, SBF and keroplatin synthesis, here we compared the transcriptional and proteomic profiles of Neoditomyia sp., O. fultoni and Arachnocampa larvae and conducted biochemical assays. Similarly to O. fultoni, Neoditomyia sp. displays an abundance of hexamerin isoforms and transcripts associated with the tryptophan and kynurenine pathway, which is potentially involved with keroplatin synthesis and silk production. Despite displaying a similar electrophoretic pattern of Orfelia luciferase purified fractions, no luciferase activity was detected in Neoditomyia purified fractions. The SBF-enriched fractions from O. fultoni and Neoditomyia revealed a similar abundance of hexamerins, the presence of flavin-dependent reductases, keroplatin and riboflavin. The results indicate that the SBF consists of protein aggregates associated with riboflavin and keroplatin, which is used as luciferin in bioluminescent species and for other still unveiled physiological functions in non-luminescent species.