Brose, Lotti et al. (2021) International Worm Meeting "Exploring neuron death in a C. elegans model of Alzheimer's disease"

Pierce, Jon, Brose, Lotti

[International Worm Meeting, 2021]

Alzheimer's disease (AD) is the leading cause of dementia worldwide and has been characterized pathologically as gross loss of neurons and neuronal connections in areas of the brain that control memory and executive function. Genetic variations in a number of genes, including amyloid precursor protein (APP) and apolipoprotein E (APOE), have been shown to influence both age of onset and severity of AD. Both an additional copy and gain-of-function mutants in APP can cause earlier onset of AD, while the e4 allele of APOE (APOE4) hastens and exacerbates AD compared to its other alleles (APOE2 and APOE3). How these genes influence neuronal health in AD has yet to be determined. Our lab has developed a C. elegans model of AD that expresses both APP and APOE4. These worms exhibit specific, age-dependent neurodegeneration and cell death that can be readily observed using fluorescent microscopy. Combined with behavioral observations, we determined that expression of APOE4, but not APOE3, leads to death of the command egg laying neuron, HSN, by middle age. Further, genetic manipulation and time-lapse microscopy suggests neurons are not dying via apoptosis. We are currently exploring additional cell death pathways, as discovering the underlying neurodegeneration mechanisms may help identify novel therapeutic targets.

Kelly Howell et al. (2002) East Coast Worm Meeting "Expression and localization of UNC-13 proteins in C. elegans"

Kristen Servent, Kelly Howell, Judith Lytle, Lynn Schwarting, Rebecca E Kohn

[East Coast Worm Meeting, 2002]

We are analyzing the expression patterns of different forms of UNC-13 proteins. unc-13 mutants are severely uncoordinated and are resistant to acetylcholinesterase inhibitors. The most abundant protein product expressed from this gene, UNC-13 LR, localizes to synapses (Kohn, 2000). UNC-13 interacts with other presynaptic proteins and affects vesicle priming (Richmond, 2001). While some mammalian homologues are found in the nervous system (Brose, 1995), the human homologue is expressed in kidneys (Song, 1999). The C. elegans unc-13 gene is predicted to express several different protein products including UNC-13 LR, UNC-13 LMR, and UNC-13 MR. L represents the left region of the protein, M represents the middle, and R represents the right. Mutations in the unc-13 L region of the gene alter expression of some protein products and result in uncoordinated movement. A large deletion in the unc-13 R region, which would eliminate all protein products, results in lethality (Kohn, 2000). We are developing antibodies to determine the localization of the different forms of UNC-13 proteins to explore the possibility that these proteins have different functions. Specifically, we are making antibodies that recognize the UNC-13 M and UNC-13 R regions. We are interested in determining whether all forms of the protein are found in neurons, and where proteins are localized within neurons. Knowledge of the localization patterns of the proteins will enable us to explore possible functions of these proteins.

Zallen JA et al. (1998) West Coast Worm Meeting "THE CONSERVED IMMUNOGLOBULIN SUPERFAMILY MEMBER SAX-3/ROBO DIRECTS MULTIPLE ASPECTS OF AXON GUIDANCE"

Zallen JA, Bargmann CI

[West Coast Worm Meeting, 1998]

The function of the nervous system depends on a precise network of connections among neurons. During development, axons navigate to their targets using conserved guidance cues and receptors. Mutations in the sax-3 gene lead to widespread misrouting of axons throughout the C. elegans nervous system. sax-3 encodes a predicted transmembrane protein with immunoglobulin-like domains and fibronectin type-3 repeats that is closely related to Drosophila Robo (Zallen et al., 1998; Kidd et al., 1998). In addition, there are also vertebrate Robo homologs (K. Brose and M.Tessier-Lavigne, personal communication), suggesting that these genes participate in a conserved guidance mechanism. In one model, SAX-3/Robo may function as a receptor in the growth cone for choosing among available substrates in the environment. sax-3 mutants exhibit defects in the guidance of pioneer axons that travel independently, as well as axons that travel together in axon bundles. For example, sax-3 mutants are defective in the guidance of many axons that travel in the nerve ring, the largest axon bundle in C. elegans. To determine where SAX-3/Robo functions to guide nerve ring axons, we examined sax-3 mosaic animals. Mosaic analysis demonstrates that SAX-3/Robo can function non-autonomously in the nerve ring. In sax-3 mosaic animals, neighboring axons have similar phenotypes regardless of whether they express sax-3, suggesting that axon guidance in the nerve ring is directed by a subset of SAX-3-expressing cells. These results are consistent with SAX-3/Robo acting in pioneer neurons, or alternatively as a ligand for a nonautonomous cell interaction. Experiments are in progress to distinguish between these models. The guidance information mediated by SAX-3/Robo acts in concert with other guidance systems in C. elegans. For example, some axons that are affected by mutations in sax-3 are similarly affected by mutations that disrupt signaling mediated by the netrin pathway (Ishii et al., 1992; Chanet al., 1996). Double mutant analysis demonstrates that SAX-3/Robo acts in parallel with the UNC-6/netrin and UNC-40/DCC guidance system to recrui amphid sensory axons to the ventral midline from their laterally positioned cell bodies. We are currently investigating in vivo interactions between sax-3 and other guidance genes to understand how growing axons integrate guidance information from multiple sources to achieve their precise trajectories.