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Wnt signalling belongs to conserved pathways and mediates cell fate decision, development, regeneration and adult tissue homeostasis. Disruption or misregulation of Wnt signalling pathway often leads to disease. Wnt proteins are hydrophobic glycoproteins which need a special receptor for transport from Golgi Apparatus to cell surface, which is called MIG-14 in Caenorhabditis elegans and Wntless (Wls) in mammals. In this study, I focus on understanding mechanisms that regulate MTM-6 protein activity. MTM-6, a lipid phosphatase associated with endosomal membrane, has been recently identified as a regulator of MIG-14/Wls trafficking in Caenorhabditis elegans. Silencing of mtm-6 leads to misregulation of some Wnt-directed processes, such as migration of Q neuroblasts progeny. This study reports identification of novel mtm-6 genetic interactors that have been found to influence migration of Q neuroblasts progeny through Wnt signalling. New knowledge about mtm-6 genetic interactions bring us near to understanding of Wnt signalling regulation. Keywords: Caenorhabditis elegans, MTM-6, SEL-5, Wntless, Wnt, endosomes, phosphoinositides, retromer

Wnt signalling is indispensible for proper development of organisms and maintaining of adult tissue homeostasis. Its disruption often leads to disease. In nematode Caenorhabditis elegans, Wnt signalling governs vast array of developmental processes, among others also migration of the Q neuroblasts and their descendants. The sole Wnt acting in this process, EGL-20, triggers the canonical β-catenin Wnt signal transduction pathway in QL but not in QR which leads to QL remaining in the posterior while the QR migrates anteriorly. This represents a useful tool for studying Wnt signalling. Recently, mutation of gene cup-4 was found to disrupt migration of the QL neuroblast in a small proportion of the mutant population. cup-4 encodes a ligand-gated ion channel family homologue and it was shown to participate in endocytosis by coelomocytes, specialized phagocytic cells in the C. elegans body cavity. Here, I present the results of my effort to determine the place of CUP-4 action in Wnt signalling and to elucidate the mechanism of its function. I found that CUP-4 acts upstream of PRY- 1/Axin, which is involved in signal transduction in signal receiving cells, and most probably downstream of adaptin AP2, which is important for recycling of Wnt cargo receptor Wntless (Wls) in Wnt producing cell. cup-4 also...