Structure of the adult central complex in Drosophila: organization of distinct neuronal subsets

Astrocyte-like glia associated with the embryonic development of the central complex in the grasshopper Schistocerca gregaria

In this study we employed the expression of the astrocyte-specific enzyme glutamine synthetase, in addition to the glia-specific marker Repo, to characterize glia cell types associated with the embryonic development of the central complex in the grasshopper Schistocerca gregaria. Double labeling experiments reveal that all glutamine synthetase-positive cells associated with the central complex are also Repo-positive and horseradish peroxidase-negative, confirming they are glia. Early in embryogenesis, prior to development of the central complex, glia form a continuous population extending from the pars intercerebralis into the region of the commissural fascicles. Subsequently, these glia redisperse to envelop each of the modules of the central complex. No glial somata are found within the central complex neuropils themselves. Since glutamine synthetase is expressed cortically in glia, it allows their processes as well as their soma locations to be visualized. Single cell reconstructions reveal one population of glia as directing extensive ensheathing processes around central complex neuropils such as the central body, while another population projects columnar-like arborizations within the central body. Such arborizations are only seen in central complex modules after their neuroarchitecture has been established suggesting that the glial arborizations project onto a prior scaffold of neurons or tracheae.

Flybrain neuron database: a comprehensive database system of the Drosophila brain neurons

The long history of neuroscience has accumulated information about numerous types of neurons in the brain of various organisms. Because such neurons have been reported in diverse publications without controlled format, it is not easy to keep track of all the known neurons in a particular nervous system. To address this issue we constructed an online database called Flybrain Neuron Database (Flybrain NDB), which serves as a platform to collect and provide information about all the types of neurons published so far in the brain of Drosophila melanogaster. Projection patterns of the identified neurons in diverse areas of the brain were recorded in a unified format, with text-based descriptions as well as images and movies wherever possible. In some cases projection sites and the distribution of the post- and presynaptic sites were determined with greater detail than described in the original publication. Information about the labeling patterns of various antibodies and expression driver strains to visualize identified neurons are provided as a separate sub-database. We also implemented a novel visualization tool with which users can interactively examine three-dimensional reconstruction of the confocal serial section images with desired viewing angles and cross sections. Comprehensive collection and versatile search function of the anatomical information reported in diverse publications make it possible to analyze possible connectivity between different brain regions. We analyzed the preferential connectivity among optic lobe layers and the plausible olfactory sensory map in the lateral horn to show the usefulness of such a database.

Learning and memory in Drosophila: behavior, genetics, and neural systems

The rich behavioral repertoire that Drosophila use to navigate in their natural environment suggests that flies can use memories to inform decisions. Development of paradigms to examine memories that restrict behavioral choice was essential in furthering our understanding of the genetics and neural systems of memory formation in the fly. Olfactory, visual, and place memory paradigms have proven influential in determining principles for the mechanisms of memory formation. Several parts of the nervous system have been shown to be important for different types of memories, including the mushroom bodies and the central complex. Thus far, about 40 genes have been linked to normal olfactory short-term memory. A subset of these genes have also been tested for a role in visual and place memory. Some genes have a common function in memory formation, specificity of action comes from where in the nervous system these genes act. Alternatively, some genes have a more restricted role in different types of memories.

Drosophila type II neuroblast lineages keep Prospero levels low to generate large clones that contribute to the adult brain central complex

Tissue homeostasis depends on the ability of stem cells to properly regulate self-renewal versus differentiation. Drosophila neural stem cells (neuroblasts) are a model system to study self-renewal and differentiation. Recent work has identified two types of larval neuroblasts that have different self-renewal/differentiation properties. Type I neuroblasts bud off a series of small basal daughter cells (ganglion mother cells) that each generate two neurons. Type II neuroblasts bud off small basal daughter cells called intermediate progenitors (INPs), with each INP generating 6 to 12 neurons. Type I neuroblasts and INPs have nuclear Asense and cytoplasmic Prospero, whereas type II neuroblasts lack both these transcription factors. Here we test whether Prospero distinguishes type I/II neuroblast identity or proliferation profile, using several newly characterized Gal4 lines. We misexpress prospero using the 19H09-Gal4 line (expressed in type II neuroblasts but no adjacent type I neuroblasts) or 9D11-Gal4 line (expressed in INPs but not type II neuroblasts). We find that differential prospero expression does not distinguish type I and type II neuroblast identities, but Prospero regulates proliferation in both type I and type II neuroblast lineages. In addition, we use 9D11 lineage tracing to show that type II lineages generate both small-field and large-field neurons within the adult central complex, a brain region required for locomotion, flight, and visual pattern memory.