Dietary dopamine causes ovary activation in queenless Apis mellifera workers

Groups of young honey bee workers were fed a diet containing dopamine while confined in small cages at 34 °C and 80% RH in absence of a queen for 8 to 13 days. The bees in eight pairs of cages, each pair containing an equal number of workers, received a pollen-rich diet supplemented with dopamine (10 $\mu$g/g of diet) (DOP groups), or not supplemented (controls). The rate of consumption of the diet was monitored continuously during the confinement period, after which the workers were dissected to assess follicle development in the ovaries. The results showed a significantly higher proportion ($P = 0.004$) of workers with activated ovaries in the DOP groups than in control groups. The number of bees surviving confinement was significantly higher in the control groups than in the DOP groups ($P \leq 0.01$), possibly reflecting a deleterious effect of dopamine. The surviving bees from both groups consumed equivalent amounts of diet ($P = 0.687$), showing that ovary activation was not due to differential diet consumption. The results suggest a role of dopamine in the chain of events mediating changes in the reproductive status of orphan honey bee workers

microRNA transcriptome from activated ovaries of Apis mellifera workers

Póster presentado en el Sixth International symposium on Molecular Insect Science, celebrado en Amsterdam entre el 2 y 5 de octubre de 2011.When driven to extremes, continuous phenotypic variation can be broken giving rise to distinct dimorphic adaptive phenotypes, as is the case in the castes of highly social insects. In these, dimorphism is built around reproductive potential, such as in the honey bee, Apis mellifera, the best studied organism in this group. Queen ovaries are large and consist of 150-200 ovarioles, whereas those of workers are small, with only few ovarioles. Even though practically sterile while a queen is present in the colony, workers can activate their ovaries and lay male-producing eggs when queenless. The factors driving this change in the state of ovary activity in workers are still poorly understood. With microRNAs knowingly involved in fine tuning genomic responses in both developmental processes as well as systemic responses to environmental change we herein investigated the miRNA transcriptome in workers undergoing ovary activation. By means of Illumina deep-sequencing of size selected (<200 nt) transcripts we obtained 35 million reads. Read length ranged from 10 to 40 nt, the majority having 19 to 24 nt. About 90% of the reads could be mapped to the honey bee genome.Furthermore, 168 of the 331 miRNAs known for Apis mellifera were represented in our dataset, some highly expressed, as for instance the miRNAs 306, 317, 184, 1-2, 1-1, 276, 71, 14, 2-3 and 2-2. Independently of the expression rates and based on literature information, the identified miRNAs are described as linked to hormonal signaling cascades (miR-14, miR-34, let-7), germ cell or ovary development (miR-7, miR-278, miR-92b, miR-989, miR-318, miR-100, let-7), embryogenesis (miR-184, miR-989, miR-1-1), cell death suppression (miR-14, miR-263-b, miR-11, miR-2-2), cell growth (miR-318, miR-315, miR-8, miR-1-2), and caste differentiation (miR-9a, miR-9b). These biological processes are consistent with the molecular changes required to the ovary activation and miRNAs emerged as regulators of the reproductive status.Peer Reviewe

miR92b and miR-9a the novel candidates as regulators of the positive reproductive status in honeybees

Póster presentado en el Sixth International symposium on Molecular Insect Science, celebrado en Amsterdam entre el 2 y 5 de octubre de 2011.In a queenright colony of Apis mellifera the workers do not reproduce. However, the workers can activate their ovaries in response to the absence of the queen. However the genetic cascade behind this process is not fully understood. In view of miRNA multiple roles in gene regulation of a variety of developmental and reproductive processes, we investigated their occurrence by analyzing 35 million reads (Illumina) of a small RNA library from active ovaries of queenless A. mellifera workers. A set of 168 miRNA previously identified in honeybees were found. Using qPCR we compared the expression of let-7, miR-184, miR-92b and miR-9a (among the most differentially represented in the library and linked to reproductive and caste differentiation processes) in active and inactive worker ovaries. The miR-184 presented consistently highest expression levels in both samples. Despite its described function in Drosophila egg formation, our data suggest that miR-184 is also important in general ovary physiology.In addition, miR-184 showed the most stable expression rates in all analyzed samples and was used as internal control to normalize the expression of other miRNAs. The involvement of let-7 in reproduction, hormonal signaling and developmental timing is known for several metazoans. Since let-7 and miR-184 showed to be expressed at similar levels in both ovary types, we postulate they govern ovary basal metabolism independent of the activation status. The expression of miR-92b and miR-9a were significantly higher in active than inactive ovaries (p <0.05). These miRNAs are related to cell cycle control in embryonic stem cells and caste differentiation, respectively. Considering that egg laying workers behave as a queen as well as their active ovaries mimics the function of a queen ovary, our results add two novel candidates as regulators of the molecular cascade leading to maintaining the positive reproductive status in honeybee female castes.Peer Reviewe