Beyond barriers: genetic control of lipid metabolism in C. elegans

Abstract

Biological life is defined and sustained by its boundaries. Cell boundaries are a complex, dynamic and active system of cell membranes and the extracellular matrix (ECM), composed of lipids, sugars and proteins. They are at the forefront of cell interaction and communication with their environment and must be constantly maintained and adjusted to resist environmental and dietary fluctuations. From regulation of membrane fluidity through fatty acid desaturation and incorporation to forward genetics screens for novel alleles that govern the development of the hermaphrodite four-cell tail tip, this thesis investigates mechanisms that govern cell boundary homeostasis and their systemic roles in organismal adaptation and development. The first section focuses on the inner boundaries and regulation of lipid homeostasis and membrane fluidity. Building on previously published work that described the first downstream “branch” of the membrane fluidity sensors AdipoR2/PAQR-2, confirming that AdipoR2/PAQR-2 can detect membrane rigidity and act through their interaction partners to upregulate the transcription of the fat-7 desaturase, promoting synthesis of fluidizing monounsaturated fatty acids (MUFAs). By using Caenorhabditis elegans and human cell models, we investigate the second downstream “branch” of the AdipoR2/PAQR-2 and demonstrate that AdipoR2/PAQR-2 acts by recruiting enzyme complexes responsible for fatty acid elongation and channeling of unsaturated fatty acids into phospholipids. The second section focuses on elucidating the most important role of polyunsaturated fatty acids (PUFAs) by screening for suppressor mutations in a PUFA deficient mutant strain. The screen revealed that mutations in the HIF-1 pathway can compensate PUFA deficiency by improving desaturase activity through accumulation of excess ferrous iron. Finally, we screened for hermaphrodite mutants with a tail end defective (Ted) phenotype, leveraging the phenotype found in paqr-2 mutants to identify novel genes and pathways involved in the regulation of cellular boundaries. The screen identified multiple genes involved in the maintenance and structure of the cuticle, adhesion systems, and membrane-associated pathways. We characterized the ptr-18 (patched-related) mutant showing multifaceted defects in the cuticle formation, membrane permeability, molting and developmental cycle, confirming a pivotal role for PTR-18 in the regulation of the apical ECM. Collectively, the research presented in this thesis deepens our understanding of cellular boundary dynamics. By bridging the gap between membrane homeostasis and ECM development, these findings ofer critical insight into the importance of cell boundary maintenance, providing a valuable model for research on metabolic interaction and adaptation to changing environments.