RESUMO
Social life is prone to invasion by microorganisms, and binding of ferric ions by transferrin is an efficient strategy to restrict their access to iron. In this study, we isolated cDNA and genomic clones encoding an Apis mellifera transferrin (AmTRF) gene. It has an open reading frame (ORF) of 2136 bp spread over nine exons. The deduced protein sequence comprises 686 amino acid residues plus a 26 residues signal sequence, giving a predicted molecular mass of 76 kDa. Comparison of the deduced AmTRF amino acid sequence with known insect transferrins revealed significant similarity extending over the entire sequence. It clusters with monoferric transferrins, with which it shares putative iron-binding residues in the N-terminal lobe. In a functional analysis of AmTRF expression in honey bee development, we monitored its expression profile in the larval and pupal stages. The negative regulation of AmTRF by ecdysteroids deduced from the developmental expression profile was confirmed by experimental treatment of spinning-stage honey bee larvae with 20-hydroxyecdysone, and of fourth instar-larvae with juvenile hormone. A juvenile hormone application to spinning-stage larvae, in contrast, had only a minor effect on AmTRF transcript levels. This is the first study implicating ecdysteroids in the developmental regulation of transferrin expression in an insect species.
Assuntos
Abelhas/genética , Ecdisteroides/fisiologia , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Genes de Insetos/genética , Hormônios Juvenis/fisiologia , Transferrina/genética , Sequência de Aminoácidos , Animais , Sequência de Bases , Abelhas/crescimento & desenvolvimento , Abelhas/metabolismo , Northern Blotting , DNA Complementar/genética , Regulação para Baixo , Ecdisterona/farmacologia , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Hormônios Juvenis/farmacologia , Larva/crescimento & desenvolvimento , Larva/metabolismo , Dados de Sequência Molecular , Filogenia , Pupa/crescimento & desenvolvimento , Pupa/metabolismo , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Transferrina/biossínteseRESUMO
Evidence from field wasps and bumblebees appoints the endocrine system as a mediator between dominance status and ovarian activity in primitively social Hymenoptera. In this comparative study on ecdysteroid titers in the highly social honey bee, Apis mellifera, and a stingless bee, Melipona quadrifasciata, we focussed on the relationship between the ecdysteroid titer, social conditions (presence or absence of the queen), and ovary activity. In contrast to bumblebees, ecdysteroid titers in honey bee and stingless bee workers were either not altered, or dropped to even lower levels after the queen was removed. We also did not detect differences between virgin queens and mated, egg laying queens. These results suggest that ecdysteroids may have lost most of their reproductive functions - yet gained functions in larval caste differentiation - as higher levels of social organization were attained in the evolution of social insects. The observation that ecdysteroid titers are transiently elevated in young workers adds a new, yet functionally still speculative facet to hormonal regulation in insect societies.