Salam, Sangeena et al. (2015) International Worm Meeting "Dopamine Modulation of Electrotactic Swimming Behavior in C. elegans."

Gupta, Bhagwati P, Mishra, Ram K, Selvaganapathy, P Ravi, Salam, Sangeena

[International Worm Meeting, 2015]

Dopamine (DA) is an important neuromodulator which is involved in controlling movement and psychological functions such as cognition and reward processing. Alteration in DA levels is associated with various neurological disorders and behavioral changes. The C. elegans nervous system consists of 302 neurons including eight dopamine neurons which has conserved dopamine pathways. DA modulate a range of behaviors such as egg laying, feeding and locomotion. In an electrotaxis behavior assay, the worms show movement towards cathode in low external DC electric filed. However, the mechanism of how DA signaling modulates electrotactic swimming is elusive. To investigate the role of DA signaling in electrotaxis behavior, we employed a novel microfluidic platform that facilitates on demand control of worm movement using electric fields. In this study we demonstrate how DA modulates the electrotactic swimming speed in a microfluidics channel. The DA deficient mutant cat-2 which encodes a tyrosine hydroxylase has a wild type like electrotactic swimming speed. DA transporter mutant dat-1 has a slow electrotactic swimming. DA deficient mutant bas-1 and cat-1 encode for aromatic amino acid decarboxylase and vesicular monoamine transporter respectively and these mutants showed a faster electrotactic speed which is partially rescued by the exogenous DA treatment. The D2 like receptor mutant dop-3 showed a faster speed suggesting that dop-3 is the primary receptor in mediating slow movement.Interestingly, we found that a prolonged exposure to electric field resulted in a gradual decline in the swimming speed such that animals were 40% slower at the end of 10 minute compared to their initial speed. This change is also mediated by the DOP-3 receptor since dop-3 mutants continue to swim at the initial speed and do not slow down. Further support to this conclusion comes from the analysis of animals treated with Heloperidol (D2 antagonist) and SKF (D1 agonist). Heloperidol either alone or in combination with SKF suppressed slowness in speed of wild type animals in the 10 min long assay. Overall, our work demonstrates that D2 receptor-mediated neuronal signaling is required to restrict muscle activity not only during the initial phase of electrotaxis swimming but also for the entire duration of the assay.

Salam, Sangeena et al. (2011) International Worm Meeting "Microfluidics approach to study neurodegeneration in a Caenorhabditis elegans Parkinson's disease model."

Selvaganapathy, P Ravi, Gupta, Bhagwati P, Rezai, Pouya, Salam, Sangeena

[International Worm Meeting, 2011]

C. elegans is an established model organism to understand the biology of neurodegenerative diseases and identify potential therapeutic targets. Parkinson's disease (PD) is one such disease that affects millions of people worldwide. A major cause of PD is the loss of dopaminergic (DA) neurons in the substantia niagra, a region of the brain that controls balance and movement. While genetic changes contribute to the development of PD, several chemical compounds, such as 6-hydroxy dopamine (6-OHDA) and methyl phenyl tetrahydropyridine (MPTP), have also been found to induce PD-like symptoms in humans by degeneration of DA neurons. C. elegans is sensitive to 6-OHDA and MPTP and exhibits movement defects. Toxin-induced worm PD models have been valuable in understanding the mechanism of neuronal degeneration and screening for potential neuroprotective compounds. Movement assays in worms typically involves observing phenotypes on plates and counting animals manually. In some cases neuronal defects are visualized by fluorescent markers such as DAT-1::GFP. This manual process is slow, subjective and measurable parameters of behavior are limited. Also, it is difficult to account for experimental conditions that lead to variations between batches. Considering these limitations, we are taking a microfluidics approach to study neurodegeneration in worms exposed to 6-OHDA, MPTP and other neurotoxins. Microfluidics offers many advantages over conventional methods of worm handling. Our lab had previously shown that a low voltage DC electric field inside a microfluidic channel stimulates worms to move towards the cathode (termed electrotaxis) (Rezai et al., 2010). We found that the electrotactic response is instantaneous, extremely sensitive, robust and benign. Although the mechanism of electrotaxis remains to be determined, it appears to be mediated by certain amphid sensory neurons. We have found that neurotoxin-treated worms are defective in electrotactic behavior. They move with variable speed with intermittent pauses and abnormal body bends. Characterization of movement defects has revealed that our assay is much more sensitive than standard plate-based drug assays and requires low drug concentrations and short exposure times (typically few hours). Using the channel, we also tested the effect of neuroprotective compounds such as Acetaminophen and found that it efficiently suppresses 6-OHDA and MPTP toxicity. Currently, we are attempting to automate the entire process of drug exposure and phenotypic analysis. The progress on these fronts will be presented.

Guasp, Ryan et al. (2019) International Worm Meeting "Trans-tissue signals from developing embryos instruct distant neurons to throw out their trash."

Guasp, Ryan, Salam, Sangeena, Harinath, Girish, Wang, Guoqiang, Driscoll, Monica, Melentijevic, Ilija

[International Worm Meeting, 2019]

The maintenance of proteostasis is critical for cell and organism function. We have reported that, in addition to internal protein quality control functions of chaperone action, proteasome-mediated degradation, and autophagy, certain C. elegans cells have the capacity to select, package and throw out their trash (Melentijevic et al., 2017). Large membrane-bound vesicles that contain protein aggregates and damaged organelles can be extruded by touch receptor neurons into the neighboring hypodermis, which attempts exopher degradation. The frequency of exopher production can be greatly exacerbated by internal proteo-stresses or by factors that disrupt mitochondrial quality. We have shown that in hermaphrodites, exophers produced by multiple neurons are generated in a distinct bi-modal pattern during adult life. We observe an initial peak in exopher production on adult day 2-3, followed by relatively low levels until around adult days 9-11 when a second peak can occur. The young adult exopher peak appears at about the time of a reconfiguration of proteostasis strategies (Ben-Zvi et al., 2009), and thus might reflect a developmental trash-elimination period in which deleterious materials accumulated during early life are collected and thrown away at one designated moment to clean house. What triggers this "trash day" is unclear. We have found that genetic and pharmacological interventions that disrupt embryogenesis can abrogate the early adult peak of exopher production. FuDR can inhibit the early peak; disruption of sperm maturation using the auxin-inducible spe-44 degron system blocks virtually all early exopher production; and genetic mutants in glp-4 and gld-1 that lack oocytes have very few early exophers. Similarly, the small-molecule drug C22, which causes embryonic lethality via increasing eggshell permeability (Weicksel et al., 2016) prevents early exopher generation. These data suggest signals associated with housing developing embryos act to ultimately increase neuronal exopher production in distant cells. Male C. elegans display a temporal and spatial distribution of exopher production distinct from hermaphrodites. In hermaphrodite touch neurons the highest rate of exopher production is from ALMR neurons with almost no production in the PLM neurons. This pattern is reversed in males. Furthermore, exophers in males increase progressively with age rather than occurring with the temporal peak pattern characteristic of hermaphrodites. These data suggest that signals associated with housing fertilized embryos modulate exopher production in hermaphrodites. We will discuss these studies with regard to understanding the molecular nature of the trans-tissue signaling.