Abstract
BackgroundHexamerins are hemocyanin-derived proteins that have lost the ability to bind copper ions and transport oxygen; instead, they became storage proteins. The current study aimed to broaden our knowledge on the hexamerin genes found in the honey bee genome by exploring their structural characteristics, expression profiles, evolution, and functions in the life cycle of workers, drones and queens.ResultsThe hexamerin genes of the honey bee (hex 70a, hex 70b, hex 70c and hex 110) diverge considerably in structure, so that the overall amino acid identity shared among their deduced protein subunits varies from 30 to 42%. Bioinformatics search for motifs in the respective upstream control regions (UCRs) revealed six overrepresented motifs including a potential binding site for Ultraspiracle (Usp), a target of juvenile hormone (JH). The expression of these genes was induced by topical application of JH on worker larvae. The four genes are highly transcribed by the larval fat body, although with significant differences in transcript levels, but only hex 110 and hex 70a are re-induced in the adult fat body in a caste- and sex-specific fashion, workers showing the highest expression. Transcripts for hex 110, hex 70a and hex70b were detected in developing ovaries and testes, and hex 110 was highly transcribed in the ovaries of egg-laying queens. A phylogenetic analysis revealed that HEX 110 is located at the most basal position among the holometabola hexamerins, and like HEX 70a and HEX 70c, it shares potential orthology relationship with hexamerins from other hymenopteran species.ConclusionsStriking differences were found in the structure and developmental expression of the four hexamerin genes in the honey bee. The presence of a potential binding site for Usp in the respective 5' UCRs, and the results of experiments on JH level manipulation in vivo support the hypothesis of regulation by JH. Transcript levels and patterns in the fat body and gonads suggest that, in addition to their primary role in supplying amino acids for metamorphosis, hexamerins serve as storage proteins for gonad development, egg production, and to support foraging activity. A phylogenetic analysis including the four deduced hexamerins and related proteins revealed a complex pattern of evolution, with independent radiation in insect orders.
Highlights
Hexamerins are hemocyanin-derived proteins that have lost the ability to bind copper ions and transport oxygen; instead, they became storage proteins
The sequencing of hex 110 was extended to the entire coding sequence (CDS) and part of the 5' and 3' untranslated region (UTR)
The hex 70a, hex 70b and hex 70c sequences are tandemly arrayed in GroupUn.53, whereas hex 110 is separately positioned in Group 11.32
Summary
Hexamerins are hemocyanin-derived proteins that have lost the ability to bind copper ions and transport oxygen; instead, they became storage proteins. Hexamerins essentially participate in the dynamics of amino acid storage and exploitation that occurs during insect development. These six-subunit proteins are primarily synthesized by the larval fat body and are massively stored in hemolymph as an amino acid source for. The highly eusocial honey bee hatches as a larva after a 72 h embryonic stage, and develops through a series of molts that define the five larval instars. This is a period of feeding, and the larva gains weight while it is continuously fed by worker bees. Duration of development from egg to adult eclosion differs considerably among queens, workers and drones, spanning 16, 21 and 24 days, respectively [17] with some differences among A. mellifera subspecies
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