A genetically encoded biosensor for visualising hypoxia responses in vivo

2017. Tvisha Misra (et al.). Biology Open 6 (2), 296-304

Article

Cells experience different oxygen concentrations depending on location, organismal developmental stage, and physiological or pathological conditions. Responses to reduced oxygen levels (hypoxia) rely on the conserved hypoxia-inducible factor 1 (HIF-1). Understanding the developmental and tissue-specific responses to changing oxygen levels has been limited by the lack of adequate tools for monitoring HIF-1 in vivo. To visualise and analyse HIF-1 dynamics in Drosophila, we used a hypoxia biosensor consisting of GFP fused to the oxygen-dependent degradation domain (ODD) of the HIF-1 homologue Sima. GFP-ODD responds to changing oxygen levels and to genetic manipulations of the hypoxia pathway, reflecting oxygen-dependent regulation of HIF-1 at the single-cell level. Ratiometric imaging of GFP-ODD and a red-fluorescent reference protein reveals tissue-specific differences in the cellular hypoxic status at ambient normoxia. Strikingly, cells in the larval brain show distinct hypoxic states that correlate with the distribution and relative densities of respiratory tubes. We present a set of genetic and image analysis tools that enable new approaches to map hypoxic microenvironments, to probe effects of perturbations on hypoxic signalling, and to identify new regulators of the hypoxia response.

Synaptic circuitry of identified neurons in the antennal lobe of Drosophila melanogaster

2016. Jürgen Rybak (et al.). Journal of Comparative Neurology 524 (9), 1920-1956

Article

In Drosophila melanogaster olfactory sensory neurons (OSNs) establish synapses with projection neurons (PNs) and local interneurons within antennal lobe (AL) glomeruli. Substantial knowledge regarding this circuitry has been obtained by functional studies, whereas ultrastructural evidence of synaptic contacts is scarce. To fill this gap, we studied serial sections of three glomeruli using electron microscopy. Ectopic expression of a membrane-bound peroxidase allowed us to map synaptic sites along PN dendrites. Our data prove for the first time that each of the three major types of AL neurons is both pre- and postsynaptic to the other two types, as previously indicated by functional studies. PN dendrites carry a large proportion of output synapses, with approximately one output per every three input synapses. Detailed reconstructions of PN dendrites showed that these synapses are distributed unevenly, with input and output sites partially segregated along a proximal-distal gradient and the thinnest branches carrying solely input synapses. Moreover, our data indicate synapse clustering, as we found evidence of dendritic tiling of PN dendrites. PN output synapses exhibited T-shaped presynaptic densities, mostly arranged as tetrads. In contrast, output synapses from putative OSNs showed elongated presynaptic densities in which the T-bar platform was supported by several pedestals and contacted as many as 20 postsynaptic profiles. We also discovered synaptic contacts between the putative OSNs. The average synaptic density in the glomerular neuropil was about two synapses/mu m(3). These results are discussed with regard to current models of olfactory glomerular microcircuits across species. J. Comp. Neurol. 524:1920-1956, 2016.

Do the Genes of the Innate Immune Response Contribute to Neuroprotection in Drosophila?

2015. Rafael Cantera, Rosa Barrio. Journal of Innate Immunity 7 (1), 3-10

Article

A profound debate exists on the relationship between neurodegeneration and the innate immune response in humans. Although it is clear that such a relation exists, the causes and consequences of this complex association remain to be determined in detail. Drosophila is being used to investigate the mechanisms involved in neurodegeneration, and all genomic studies on this issue have generated gene catalogues enriched in genes of the innate immune response. We review the data reported in these publications and propose that the abundance of immune genes in studies of neurodegeneration reflects at least two phenomena: (i) some proteins have functions in both immune and nervous systems, and (ii) immune genes might also be of neuroprotective value in Drosophila. This review opens this debate in Drosophila, which could thus be used as an instrumental model to elucidate this question.

Rafael Cantera

Publications

A genetically encoded biosensor for visualising hypoxia responses in vivo

Synaptic circuitry of identified neurons in the antennal lobe of Drosophila melanogaster

Do the Genes of the Innate Immune Response Contribute to Neuroprotection in Drosophila?