LarvaSPA, A Method for Mounting Drosophila Larva for Long-Term Time-Lapse Imaging

In vivo optogenetic manipulations of endogenous proteins reveal spatiotemporal roles of microtubule and kinesin in dendrite patterning

During animal development, the spatiotemporal properties of molecular events largely determine the biological outcomes. Conventional gene analysis methods lack the spatiotemporal resolution for precise dissection of developmental mechanisms. Although optogenetic tools exist for manipulating designer proteins in cultured cells, few have been successfully applied to endogenous proteins in live animals. Here, we report OptoTrap, a light-inducible clustering system for manipulating endogenous proteins of diverse sizes, subcellular locations, and functions in Drosophila. This system turns on fast, is reversible in minutes or hours, and contains variants optimized for neurons and epithelial cells. By using OptoTrap to disrupt microtubules and inhibit kinesin-1 in neurons, we show that microtubules support the growth of highly dynamic dendrites and that kinesin-1 is required for patterning of low- and high-order dendritic branches in differential spatiotemporal domains. OptoTrap allows for precise manipulation of endogenous proteins in a spatiotemporal manner and thus holds promise for studying developmental mechanisms in a wide range of cell types and developmental stages.

Protocol for Imaging the Same Class IV Neurons at Different Stages of Development

In this protocol, we focused on analyzing internal branches of Drosophila class IV neurons. These neurons are characterized by their highly branched axons and dendrites and intricately tile the larval body. As Drosophila larvae progress through developmental stages, the dendritic arbors of Class IV neurons undergo notable transformations. As Drosophila larvae develop, their Class IV dendritic arbors grow. In the initial 24 h after egg laying (AEL), the dendrites are smaller than segments. During the subsequent 24 h of the first instar larval stage, dendritic arbors outpace segment growth, achieving tiling. After 48 h, arbors and segments grow concurrently. Epidermal cells near Class IV dendrites expand in proportion to segment growth. This observation suggested that Class IV cells might grow via branch dilation-uniformly elongating branches, akin to Class I cells [1,2]. To understand whether the class IV complex arbor structure is formed by dilation or simply from growing tips, we developed this protocol to introduce a systematic approach for quantitatively assessing the growth dynamics of internal branches. Key features • This protocol employs imaging the same neuron over different development times • Drosophila embryo and larvae genotype is ;;ppkCD4-tdGFP, which explicitly tags class IV neurons • This protocol for the preparation of agar pads to mount and image Drosophila larvae is adapted from Monica Driscoll's method • Neurons are imaged without the use of anesthetics and for a short duration of time • This technique involves the use of a spinning disk confocal microscope.

Light-induced trapping of endogenous proteins reveals spatiotemporal roles of microtubule and kinesin-1 in dendrite patterning of Drosophila sensory neurons

Animal development involves numerous molecular events, whose spatiotemporal properties largely determine the biological outcomes. Conventional methods for studying gene function lack the necessary spatiotemporal resolution for precise dissection of developmental mechanisms. Optogenetic approaches are powerful alternatives, but most existing tools rely on exogenous designer proteins that produce narrow outputs and cannot be applied to diverse or endogenous proteins. To address this limitation, we developed OptoTrap, a light-inducible protein trapping system that allows manipulation of endogenous proteins tagged with GFP or split GFP. This system turns on fast and is reversible in minutes or hours. We generated OptoTrap variants optimized for neurons and epithelial cells and demonstrate effective trapping of endogenous proteins of diverse sizes, subcellular locations, and functions. Furthermore, OptoTrap allowed us to instantly disrupt microtubules and inhibit the kinesin-1 motor in specific dendritic branches of Drosophila sensory neurons. Using OptoTrap, we obtained direct evidence that microtubules support the growth of highly dynamic dendrites. Similarly, targeted manipulation of Kinesin heavy chain revealed differential spatiotemporal requirements of kinesin-1 in the patterning of low- and high-order dendritic branches, suggesting that different cargos are needed for the growth of these branches. OptoTrap allows for precise manipulation of endogenous proteins in a spatiotemporal manner and thus holds great promise for studying developmental mechanisms in a wide range of cell types and developmental stages.

The Drosophila chemokine-like Orion bridges phosphatidylserine and Draper in phagocytosis of neurons

Phagocytic clearance of degenerating neurons is triggered by "eat-me" signals exposed on the neuronal surface. The conserved neuronal eat-me signal phosphatidylserine (PS) and the engulfment receptor Draper (Drpr) mediate phagocytosis of degenerating neurons in Drosophila. However, how PS is recognized by Drpr-expressing phagocytes in vivo remains poorly understood. Using multiple models of dendrite degeneration, we show that the Drosophila chemokine-like protein Orion can bind to PS and is responsible for detecting PS exposure on neurons; it is supplied cell-non-autonomously to coat PS-exposing dendrites and to mediate interactions between PS and Drpr, thus enabling phagocytosis. As a result, the accumulation of Orion on neurons and on phagocytes produces opposite outcomes by potentiating and suppressing phagocytosis, respectively. Moreover, the Orion dosage is a key determinant of the sensitivity of phagocytes to PS exposed on neurons. Lastly, mutagenesis analyses show that the sequence motifs shared between Orion and human immunomodulatory proteins are important for Orion function. Thus, our results uncover a missing link in PS-mediated phagocytosis in Drosophila and imply conserved mechanisms of phagocytosis of neurons.

A photo-switchable assay system for dendrite degeneration and repair in Drosophila melanogaster

Neurodegeneration arising from aging, injury, or diseases has devastating health consequences. Whereas neuronal survival and axon degeneration have been studied extensively, much less is known about how neurodegeneration affects dendrites, in part due to the limited assay systems available. To develop an assay for dendrite degeneration and repair, we used photo-switchable caspase-3 (caspase-Light-Oxygen-Voltage-sensing [caspase-LOV]) in peripheral class 4 dendrite arborization (c4da) neurons to induce graded neurodegeneration by adjusting illumination duration during development and adulthood in Drosophila melanogaster. We found that both developing and mature c4da neurons were able to survive while sustaining mild neurodegeneration induced by moderate caspase-LOV activation. Further, we observed active dendrite addition and dendrite regeneration in developing and mature c4da neurons, respectively. Using this assay, we found that the mouse Wallerian degeneration slow (Wld^S) protein can protect c4da neurons from caspase-LOV-induced dendrite degeneration and cell death. Furthermore, our data show that Wld^S can reduce dendrite elimination without affecting dendrite addition. In summary, we successfully established a photo-switchable assay system in both developing and mature neurons and used Wld^S as a test case to study the mechanisms underlying dendrite regeneration and repair.

Tumor Allotransplantation in Drosophila melanogaster with a Programmable Auto-Nanoliter Injector

This protocol describes the allotransplantation of tumors in Drosophila melanogaster using an auto-nanoliter injection apparatus. With the use of an autoinjector apparatus, trained operators can achieve more efficient and consistent transplantation results compared to those obtained using a manual injector. Here, we cover topics in a chronological fashion: from the crossing of Drosophila lines, to the induction and dissection of the primary tumor, transplantation of the primary tumor into a new adult host and continued generational transplantation of the tumor for extended studies. As a demonstration, here we use Notch intracellular domain (NICD) overexpression induced salivary gland imaginal ring tumors for generational transplantation. These tumors can first be reliably induced in a transition-zone microenvironment within larval salivary gland imaginal rings, then allografted and cultured in vivo to study continued tumor growth, evolution, and metastasis. This allotransplantation method can be useful in potential drug screening programs, as well as for studying tumor-host interactions.