INVESTIGATING NEURODEVELOPMENTAL DEFECTS CAUSED BY LOSS OF NIEMANN-PICK TYPE C DISEASE GENE1 (NPC1)

Abstract

Previous studies have studied the neurodegenerative defects caused by Niemann-Pick Type C (NPC) Disease, but very little is known about the neurodevelopmental defects and the genetic mechanisms behind the disorder. Our research focuses on ncr-1, an ortholog of NPC associated gene NPC1, and how it leads to defects in ALM polarity and late endosomal puncta motility in C. elegans. It also focuses on the genetic interactions with ncr-1 to understand the mechanisms behind NPC. In chapter two, we investigate the genetic interactions with NCR-1 and their effect on ALM polarity, late endosomal and lysosomal puncta motility, and AVM guidance. We first demonstrate NCR-1 is necessary for proper ALM polarity and show it functions in the endolysosomal system. We then provide evidence that NCR-1 is needed for late endosomal puncta motility at the proximal end of the ALM neuron; however, we find it is not necessary for lysosomal puncta motility. We discover that increasing cholesterol concentrations in plate media rescues the ALM polarity and late endosomal puncta motility defects in ncr-1 mutants. We show that NCR-1 and SLT-1, a C. elegans ortholog of human SLIT, interact differently for ALM late endosome puncta motility and ALM polarization. Late endosome puncta motility analysis demonstrates NCR-1 prevents dysfunctional SLT-1 signaling; whereas polarization analysis demonstrates a working model that SLT-1 signaling suppresses NCR-1. We find that NCR-1 and NCR-2 function additively and synergistically, respectively, to EGL-19, a C. elegans ortholog of human CACNA1C, to promote proper ALM polarity under standard, high cholesterol, and chloroquine plate media conditions. Lastly, we found that NCR-1 does not affect AVM axon guidance on its own; however, we have a working model that SLT-1 signaling suppresses NCR-1 in the AVM under standard conditions. Additionally, high cholesterol represses/weakens SLT-1 signaling. Lastly, the loss of NCR-1 is not affected by chloroquine treatment but does affect SLT-1 and possibly other AVM guidance pathways.