Study of the CTP Synthetase Filament Formation in Drosophila melanogaster

• Main Authors: Ebrima D. Cham, 陳亞德
• Other Authors: L. M. Pai
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/juaj9v

碩士 === 長庚大學 === 分子醫學全英語碩士學位學程 === 104 === CTP synthetase (CTPsyn) is an enzyme that plays a key role in nucleotide metabolism. Several studies have demonstrated that CTPsyn can form an evolutionarily conserved subcellular structure termed cytoophidium. CTPsyn is the rate limiting enzyme in the de novo CTP nucleotide biosynthesis. Hence, it is known this enzyme could be subjected to numerous regulatory mechanisms and strategies. This cytoophidium comprising of the nucleotide biosynthetic enzyme has been described in many organisms ranging from bacteria to mammals. When deprived of nutrients in yeast, CTPsyn forms filamentous structures. However, it still remains elusive whether these filaments are in the active form. As a result, the actual roles these structures play in the nucleotide CTP biosynthesis is until now widely unknown. There are two types of CTPsyn filaments found in Drosophila ovary. One type is the small rod shape cytoophidium in follicle cells, and the other type is the large curved cytoophidium in the germline cells. However, in some tissues such as wing disc or middle brain, CTPsyn filaments form only under stress induction. In our lab, we are currently working on understanding how the filamentous structure is formed by generating point mutations in CTPsyn. We are examining which amino acids are critical for cytoophidium formation. It is reported that point mutations at critical residues in the tetramer and dimer interfaces of CTPsyn have an effect on cytoophidium formation in Drosophila S2 cells. These results could indicate that CTPsyn multimers may be incorporated into cytoophidia. It is unclear whether CTPsyn monomers, dimers or tetramers are incorporated into cytoophidia in follicle cells where filament exist even though the nutrition is sufficient. We therefore decided to investigate the effect of mutations at the tetramer or dimer interfaces of CTPsyn on cytoophidium assembly in tissues with naturally existing filaments, and in tissues with inducible filaments. We also investigated residues involving feedback regulation and mutation in cancer patients.