Alternative splicing of a single transcription factor drives selfish reproductive behavior in honeybee workers ( Apis mellifera )

Abstract

In eusocial insects the production of daughters is generally restricted to mated queens, and unmated workers are functionally sterile. The evolution of this worker sterility has been plausibly explained by kin selection theory [Hamilton W (1964) J Theor Biol 7:1-52], and many traits have evolved to prevent conflict over reproduction among the females in an insect colony. In honeybees (Apis mellifera), worker reproduction is regulated by the queen, brood pheromones, and worker policing. However, workers of the Cape honeybee, Apis mellifera capensis, can evade this control and establish themselves as social parasites by activating their ovaries, parthenogenetically producing diploid female offspring (thelytoky) and producing queen-like amounts of queen pheromones. All these traits have been shown to be strongly influenced by a single locus on chromosome 13 [Lattorff HMG, et al. (2007) Biol Lett 3:292-295]. We screened this region for candidate genes and found that alternative splicing of a gene homologous to the gemini transcription factor of Drosophila controls worker sterility. Knocking out the critical exon in a series of RNAi experiments resulted in rapid worker ovary activation-one of the traits characteristic of the social parasites. This genetic switch may be controlled by a short intronic splice enhancer motif of nine nucleotides attached to the alternative splice site. The lack of this motif in parasitic Cape honeybee clones suggests that the removal of nine nucleotides from the altruistic worker genome may be sufficient to turn a honeybee from an altruistic worker into a parasite.caste determination | cuticular protein 2-family | gene expression T he evolution of a sterile worker caste in eusocial hymenoptera has been plausibly explained by inclusive fitness theory (1). Generally, workers refrain from reproduction as a result of intracolonial reproductive hierarchies. Ovary activation in honeybee workers (Apis mellifera) is inhibited by the pheromones from the queen and the brood (2). In addition, the multiple mating of the queen and the coexistence of many half-sibling subfamilies in the colony facilitates worker policing, where workers remove eggs laid by other workers (3), leading to <1% of worker-laid offspring (4).These mechanisms often fail, however, to control worker reproduction of the Cape honeybee (Apis mellifera capensis). In this subspecies, laying workers can function as social parasites invading foreign colonies, killing the resident queen and establishing themselves as pseudoqueens (5-7). The proximate mechanisms for this parasitic life history strategy are well understood (8). Parasitic pseudoqueen workers produce a queen-like pheromonal bouquet indicating the presence of a queen to the host workers (9-13). Moreover, the diploid offspring of the parasitizing workers produce brood pheromones, suggesting the presence of a laying queen to the host workers and preventing these workers from activating their ovaries. Finally, the diploid eggs laid by the parasitic workers are not policed as pr...

Molecular signatures of plastic phenotypes in two eusocial insect species with simple societies

“…3E). This result may limit the role of DNA methylation in regulating phenotype-associated gene expression or alternative splicing in our species, and contrasts with what has been described in the honey bee (26,(35)(36)(37)(38)(39).…”

RNA interference knockdown of DNA methyl-transferase 3 affects gene alternative splicing in the honey bee

“…AS has been shown to play fundamental roles in sex determination, development, behavior, and disease, and in worker honey bees, sterility, which is a hallmark of eusociality (1,34,35). Recently, DNA methylation has been detected in the genomes of other important social insects including several ants and termites (36,37) and has been implicated in caste differentiation and behavioral maturation (8,38).…”

Negligible uptake and transfer of diet-derived pollen microRNAs in adult honey bees

“…In agreement, oral administration of dsRNA appears to be effective at regulation of gene expression in honey bees. [69][70][71][72][73][74][75][76] In addition, high dose injection of dsRNAs into the hemocoel has been used for delivery and inhibition of target genes in multiple tissues in this species [77][78][79][80][81][82][83][84][85][86] independent of the site of injection, demonstrating that these molecules can be efficiently taken up by disparate tissues once in the open circulatory system. Our results, in conjunction with the previous studies using dsRNA in other insect species, suggest that uptake of longer dsRNAs may be more efficient than shorter miRNAs.…”