Biogenic amines and their receptors regulate and modulate many physiological and behavioural processes in animals. In vertebrates, octopamine is only found in trace amounts and its function as a true neurotransmitter is unclear. In protostomes, however, octopamine can act as neurotransmitter, neuromodulator and neurohormone. In the honeybee, octopamine acts as a neuromodulator and is involved in learning and memory formation. The identification of potential octopamine receptors is decisive for an understanding of the cellular pathways involved in mediating the effects of octopamine. Here we report the cloning and functional characterization of the first octopamine receptor from the honeybee, Apis mellifera. The gene was isolated from a brain-specific cDNA library. It encodes a protein most closely related to octopamine receptors from Drosophila melanogaster and Lymnea stagnalis. Signalling properties of the cloned receptor were studied in transiently transfected human embryonic kidney (HEK) 293 cells. Nanomolar to micromolar concentrations of octopamine induced oscillatory increases in the intracellular Ca 2+ concentration. In contrast to octopamine, tyramine only elicited Ca 2+ responses at micromolar concentrations. The gene is abundantly expressed in many somata of the honeybee brain, suggesting that this octopamine receptor is involved in the processing of sensory inputs, antennal motor outputs and higher-order brain functions.

Sex determination in Hymenoptera is controlled by haplo-diploidy in which unfertilized eggs develop into fertile haploid males. A single sex determination locus with several complementary alleles was proposed for Hymenoptera [so-called complementary sex determination (CSD)]. Heterozygotes at the sex determination locus are normal, fertile females, whereas diploid zygotes that are homozygous develop into sterile males. This results in a strong heterozygote advantage, and the sex locus exhibits extreme polymorphism maintained by overdominant selection. We characterized the sex-determining region by genetic linkage and physical mapping analyses. Detailed linkage and physical mapping studies showed that the recombination rate is <44 kb/cM in the sex-determining region. Comparing genetic map distance along the linkage group III in three crosses revealed a large marker gap in the sex-determining region, suggesting that the recombination rate is high. We suggest that a “hotspot” for recombination has resulted here because of selection for combining favorable genotypes, and perhaps as a result of selection against deleterious mutations. The mapping data, based on long-range restriction mapping, suggest that the Q DNA-marker is within 20,000 bp of the sex locus, which should accelerate molecular analyses.

honeybee / Apis mellifera / PFGE / physical mapping Although the honeybee is not a basic genetic model organism so far, the complex behavioural repertoire, the male haploidy, the extremely high rate of recombination and recent QTL and mapping studies have shown that the honeybee is becoming a model organism for genomic studies of naturally occurring traits [5,7] and sex determination [1,6] KCl,7.5 mM NaCl, 7.5 mM Tris, 0.1 mM sperminc, 0.25 mM spermidine, 0.5 M sucrose, 0.5 % Triton X-100, pH 7.4) and centrifuged at 8 000 g (4 °C) for 10 min in a SS34 rotor (Sorvall™).The supernatant and the fat at the top were carefully removed while the tube was directly cooled on ice. The remaining fat was wiped immediately from the inner surface of the tube using a paper tissue. The pellet containing the nuclei was resuspended in an equal volume of 125 mM EDTA, pH 7.5 (of about 300 μL) and mixed with an equal volume of prewarmed (45 °C) 1.5 % low melting agarose (in 125 mM EDTA, pH 7.5). The suspension was pipetted into insert moulds and cooled at 4 °C for gelling. Agarose inserts were treated with Proteinase K (2 mg·mL -1 ) in NDS-buffer (0.5 M EDTA, 10 mM Tris, pH 9, 1 % Sarkosyl) for a minimum of 24 h at 50 °C.

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