My Ph.D. research project in the Bhagwati Gupta lab focuses on understanding the mechanism by which the Axin family of scaffolding proteins functions to regulate biological processes in multicellular eukaryotes. Towards this, I am using the nematode (worm) Caenorhabditis elegans as an animal model to investigate the role of one of the Axin homologs, PRY-1. Studies in various model systems and humans have shown that the Axin family of proteins plays crucial roles during cell proliferation, cell differentiation, and organ formation. Such a role of Axin depends on the negative regulation of the WNT signaling cascade. Consistent with these, alterations in Axin function are associated with developmental abnormalities and age-associated diseases such as axis duplication, neuroectodermal defect, and muscle degeneration. As a scaffolding protein, Axin family members bind to and recruit multiple protein partners that are both WNT dependent and independent. However, how Axin interacts with these factors to regulate molecular events is not well understood. While some Axin-interacting factors have been identified, many more remain to be discovered. My project deals with the identification and functional characterization of pry-1/Axin interactors in C. elegans. The key findings of my Ph.D. research are published in five peer-reviewed papers. Collectively, the results demonstrate that PRY-1 is necessary to regulate lipid metabolism, stress response, muscle health, and aging. I have shown that PRY-1 utilizes multiple pathways to control these diverse processes. Specifically, PRY-1 functions via the SREBP transcription factor homolog SBP-1 to regulate yolk lipoprotein expression to promote lipid synthesis. The analysis of pry-1’s role in aging and muscle health has revealed its interactions with the energy sensor AMPK homolog AAK-2, thereby affecting the function of the Insulin/IGF1 signaling (IIS) transcriptional regulator DAF-16/FOXO. Moreover, I have identified several mRNA genes and microRNAs that function downstream of PRY-1/Axin signaling to either suppress or enhance pry-1 mutant defects. All these novel interactors have mammalian homologs. Altogether, these findings form the basis to pursue future work to investigate the conserved mechanism of Axin signaling and hold the potential for effective intervention to delay aging and age-associated muscle deterioration. / Thesis / Doctor of Philosophy (PhD)

Evolutionary variations during vulval development in C. elegans and its related nematode species are well analyzed. The formation of C. elegans vulva involves many complex cell-cell interactions that are mediated through well conserved EGF/EGFR/RAS, LIN12/Notch and WNT signaling pathways. These pathways specify distinct cell fates of the six epidermal vulval precursor cells (VPCs), P(3-8).p. pry-1/Axin in C. elegans is identified as a part of destruction box complex that mediates (beta)-catenin degradation and is known to negatively regulate canonical Wnt signaling pathway during its development. I focused on the genetic analysis of pry-1 I Axin function in C. briggsae, sister species to C. elegans, to study inter-species comparisons of vulva formation. Three alleles, lin(sy5353), lin(sy5411) and lin(sy5270) were genetically mapped to LG I using standard genetic and in del mapping techniques. Interestingly, a unique simultaneous Multi vulva and Vulvaless (Muv-Vul) phenotype was observed during vulva formation in Cbr-pry-1 alleles, resulting from the varying induction potentials of the VPCs along the A/P axis, compared to Cel-pry-1 animals. In order to analyze these phenotypic differences between Cel-pry-1 and Cbr-pry-1 in greater detail, I dissected vulval development in sy5353 animals. VPC competence analysis was done through cell lineages and ablations studies, while the C. briggsae vulval cell fate markers were used for cell fate specification analysis. Cell ablations revealed that P7.p and P8.p in Cbr-pry-1 animals exhibited non-competence towards anchor cell signaling. Additionally, gonad-independent inductions was observed in P(3-8).p cells and they adopted 2° cell fate specifications. Using RNAi approach, Cbr-pry-1 interactions with other vulval pathway genes were dissected and it was observed that Cbr-lin-12 is involved in VPC competence of P7.p and Cbr-pop-1 exhibited different regulatory levels during vulval development compared to C. elegans. Thus, it can be inferred that the mechanisms of vulva formation in C. briggsae has evolved through changes in the competence of VPCs. / Thesis / Master of Science (MS)