Gradients of signaling proteins are essential for inducing tissue morphogenesis. However, mechanisms of gradient formation remain controversial. Here we characterized the distribution of fluorescently-tagged signaling proteins, FGF and FGFR, expressed at physiological levels from the genomic knock-in alleles in Drosophila. FGF produced in the larval wing imaginal-disc moves to the air-sac-primordium (ASP) through FGFR-containing cytonemes that extend from the ASP to contact the wing-disc source. The number of FGF-receiving cytonemes extended by ASP cells decreases gradually with increasing distance from the source, generating a recipient-specific FGF gradient. Acting as a morphogen in the ASP, FGF activates concentration-dependent gene expression, inducing pointed-P1 at higher and cut at lower levels. The transcription-factors Pointed-P1 and Cut antagonize each other and differentially regulate formation of FGFR-containing cytonemes, creating regions with higher-to-lower numbers of FGF-receiving cytonemes. These results reveal a robust mechanism where morphogens self-generate precise tissue-specific gradient contours through feedback regulation of cytoneme-mediated dispersion.

Bnl controls tracheal development in Drosophila, but it is unclear how this fibroblast growth factor is prepared for tissue-specific dispersal. Sohr et al. find that Furin1 cleaves Bnl in the Golgi, which polarizes its sorting to the basal surface of the source cells and determines its range of cytoneme-mediated intercellular dispersion, signaling, and branching morphogenesis.

Honey bee health is mainly affected by Varroa destructor, viruses, Nosema spp., pesticide residues and poor nutrition. Interactions between these proposed factors may be responsible for the colony losses reported worldwide in recent years. In the present study, the effects of a honey bee virus, Israeli acute paralysis virus (IAPV), on the foraging behaviors and homing ability of European honey bees (Apis mellifera L.) were investigated based on proboscis extension response (PER) assays and radio frequency identification (RFID) systems. The pollen forager honey bees originated from colonies that had no detectable level of honey bee viruses and were manually inoculated with IAPV to induce the viral infection. The results showed that IAPV-inoculated honey bees were more responsive to low sucrose solutions compared to that of non-infected foragers. After two days of infection, around 107 copies of IAPV were detected in the heads of these honey bees. The homing ability of IAPV-infected foragers was depressed significantly in comparison to the homing ability of uninfected foragers. The data provided evidence that IAPV infection in the heads may enable the virus to disorder foraging roles of honey bees and to interfere with brain functions that are responsible for learning, navigation, and orientation in the honey bees, thus, making honey bees have a lower response threshold to sucrose and lose their way back to the hive.

Ovarian activity not only influences fertility, but is also involved with the regulation of division of labour between reproductive and behavioural castes of female honey bees. In order to identify candidate genes associated with ovarian activity, we compared the gene expression patterns between inactivated and activated ovaries of queens and workers by means of high-throughput RNA-sequencing technology. A total of 1615 differentially expressed genes (DEGs) was detected between ovaries of virgin and mated queens, and more than 5300 DEGs were detected between inactivated and activated worker ovaries. Intersection analysis of DEGs amongst five libraries revealed that a similar set of genes (824) participated in the ovary activation of both queens and workers. A large number of these DEGs were predominantly related to cellular, cell and cell part, binding, biological regulation and metabolic processes. In addition, over 1000 DEGs were linked to more than 230 components of Kyoto Encyclopedia of Genes and Genomes pathways, including 25 signalling pathways. The reliability of the RNA-sequencing results was confirmed by means of quantitative real-time PCR. Our results provide new insights into the molecular mechanisms involved in ovary activation and reproductive division of labour.

Nosema ceranae Fries et al., 1996, a microsporidian parasite recently transferred from Asian honey bees Apis cerana F., 1793, to European honey bees Apis mellifera L., 1758, has been suspected as one of the major culprits of the worldwide honey bee colony losses. Spore load is a commonly used criterion to describe the intensity of Nosema infection. In this study, by providing Nosema-infected bees with sterilized pollen, we confirmed that pollen feeding increased the spore loads of honey bees by several times either in the presence or absence of a queen. By changing the amount of pollen consumed by bees in cages, we showed that spore loads increased with an increase in pollen consumption. Nosema infections decrease honey bee longevity and transcription of vitellogenin, either with or without pollen feeding. However, the reduction of pollen consumption had a greater impact on honey bee longevity and vitellogenin level than the increase of spore counts caused by pollen feeding. These results indicate that spore loads may not be used alone as a direct indicator of the severity of N. ceranae infection in honey bees.