Untangling the wiring of the Drosophila visual system: developmental principles and molecular strategies.

The assembly of neural circuits relies on the accurate establishment of connections between synaptic partners. Precise wiring results from responses that neurons elicit to environmental cues and cell-cell contact events during development. A common design principle in both invertebrate and vertebrate adult nervous systems is the orderly array of columnar and layered synaptic units of certain neuropils. This similarity is particularly striking in the visual system, both at the structural and cell-type levels. Given the powerful genetic approaches and tools available in Drosophila, the fly visual system has been extensively used to probe how specific wiring patterns are achieved during development. In this review, we cover the developmental principles and molecular strategies that govern the assembly of columnar units (lamina cartridges and medulla columns), the formation of layers, afferent specific layer selection, and synaptogenesis in Drosophila. The mechanisms include: sequential developmental steps that ensure coordinated assembly of synaptic partners; anterograde and autocrine signaling; interactions between cell-surface molecules, or secreted molecules and their receptors that take place among neurons; and glia signaling to neurons.

The Cytoplasmic LIM Domain Protein Espinas Contributes to Photoreceptor Layer Selection in the Visual System.

During circuit assembly it is essential that neurons connect with their specific synaptic partners. To facilitate this process, a common strategy in many organisms is the organization of brain regions, including the fly visual system, in layers and columns. The atypical-cadherin Flamingo (Fmi) and the receptor Golden Goal (Gogo) were proposed to regulate both the temporary and final layer selection of the R8 photoreceptor, through the cytoplasmic domain of Gogo. Our data suggests that Fmi intracellular signaling is also relevant for R8 final layer selection. The LIM-domain cytoplasmic molecule Espinas (Esn) binds Fmi, and they cooperatively control dendritic self-avoidance in sensory neurons. We observed defects in R8 layer selection in esn mutants with axons overshooting the final target layer, and we demonstrated that the LIM domain is necessary for layer selection. fmi knockdown in photoreceptors results in most R8 axons stalling at the temporary layer, however, we also detected R8 axons projecting past the final-target layer, and showed that fmi and esn genetically interact. Based on the previously described physical and genetic interactions between Fmi/Esn and the findings presented here, we propose that Esn signals downstream of Fmi to stabilize R8 axons in their final target layer.

Bryostatin activates HIV-1 latent expression in human astrocytes through a PKC and NF-ĸB-dependent mechanism.

Multiple studies have shown that HIV-1 patients may develop virus reservoirs that impede eradication; these reservoirs include the central nervous system (CNS). Despite an undetectable viral load in patients treated with potent antiretrovirals, current therapy is unable to purge the virus from these latent reservoirs. To broaden the inhibitory range and effectiveness of current antiretrovirals, the potential of bryostatin was investigated as a latent HIV-1 activator. We used primary astrocytes, NHA cells, and astrocytoma cells U-87. Infected cells with HIV-1(NL4.3) were treated with bryostatin alone or in combination with different inhibitors. HIV-1 production was quantified by using ELISA. Transcriptional activity was measured using luciferase reporter gene assays by using lipofectin. We performed cotransfection experiments of the LTR promoter with the active NF-κB member p65/relA. To confirm the NF-κB role, Western blot and confocal microscopy were performed. Bryostatin reactivates latent viral infection in the NHA and U87 cells via activation of protein kinase C (PKC)-alpha and -delta, because the PKC inhibitors rottlerin and GF109203X abrogated the bryostatin effect. No alteration in cell proliferation was found. Moreover, bryostatin strongly stimulated LTR transcription by activating the transcription factor NF-κB. Bryostatin could be a beneficial adjunct to the treatment of HIV-1 brain infection.

A new chimeric protein represses HIV-1 LTR-mediated expression by DNA methylase.

Once the human immunodeficiency virus (HIV) genome is inserted into the host genome, the virus cannot be removed, which results in latency periods and makes it difficult to eradicate. The majority of strategies to eradicate HIV have been based on preventing virus latency, thereby enabling antiretroviral drugs to act against HIV replication. Another innovative strategy is permanently silencing the integrated virus to prevent the spread of infection. Epigenetic processes are natural mechanisms that can silence viral replication. We describe a new chimeric protein (IN3b) that consists of a HIV-1 integrase domain, which recognises the HIV long terminal repeat (LTR) and the catalytic domain of DNA methyltransferase DNMT3b. Our objective was to silence HIV replication by the specific delivery of the catalytic methyltransferase domain to the LTR promoter to induce its methylation. We found that our IN3b chimeric protein was expressed in the nucleus and decreased LTR-associated HIV genome expression and HIV replication. Therefore, the IN3b chimeric protein may be an effective tool against HIV replication and maybe used in a new line of research to induce or maintain HIV latency.