Expressão dos genes feminizantes fem e vitelogenina durante as fases de desenvolvimento da abelha sem ferrão Melipona interrupta (Hymenoptera: Apidae)

Abstract

In Hymenoptera, sex is determined by haplodiploidy, where males are haploid, not from eggs fertilized, and females are diploid, arising from fertilized eggs. The occurrence of diploid males, derived from fertilized eggs, has proposed that sex determination in this order is not governed by the fertilization process, but is regulated by a single genetic locus that promotes the initial signal for sex determination, the sex determination locus (SDL), which consists of five predicted genes, among which is the gene fem. The fem is the second gene in the regulatory cascade in Apis and plays a role in sex determination by differential activity of proteins from their sex-specific transcripts. After the sexual destiny is determined, female bees will differ in reproductive castes (queens) or non-reproductive (workers). In the species of Melipona, caste differentiation is through genetic-food system, which postulates that this process would result from the combination of two genes (xa and xb), which each have two alleles, where the double heterozygous results in queen phenotype and homozygosity for one or both results in the phenotype of workers. Recent studies of caste-specific gene expression show that vitellogenin is involved in the regulation of genes involved in differentiation of the queen caste and division of labor among workers. The present study was aimed to analyse the relative expression levels of the fem and vitellogenin genes through at different stages of development, sex and caste in Melipona interrupta. The fem gene is expressed in all developmental stages analyzed, and in both sexes and castes. The greatest expression of fem, observed in the larval stages, confirms the data that the variant female is involved in sex determination and also suggests an additional function related to the castes differentiation. The variation of the relative expression of fem between the pupal and adult stages was not statistically significant, suggesting that the fem is not regulated at the transcriptional level. As well as fem, vitellogenin transcripts were detected in all stages of development analyzed, and in both sexes and castes. The expression of vitellogenin can be regulated differently between castes, since we observed contrasting expression patterns between them. The expression of vitellogenin in queens may be related to their reproductive role, while workers may be related to its function in polyethism age, and males in the acquisition of alternative functions. Significant differences in relative expression of vitellogenin between the sexes and castes were observed throughout pupal development, suggesting that this gene may be involved in caste differentiation.