Consequences of Misregulated Ribonucleotide Reductase on Cell Growth, Proliferation, and Survival in the Drosophila Embryo

Abstract

The enzyme Ribonucleotide Reductase (RNR) catalyzes the rate-limiting step in the creation of deoxyribonucleoside triphosphates (dNTPs) by reducing ribonucleoside diphosphates (NDPs) [1]. Specifically, RNR converts ADP to dADP, GDP to dGDP, CDP to dCDP, and UDP to dUDP, which are then phosphorylated to make dNTPs [2]. The fidelity of DNA replication and genomic stability rely on these dNTPs and their presence in sufficient and correctly balanced amounts [1, 3]. Unbalanced, excessive, and deficient dNTP pools caused by misregulated RNR can have detrimental mutagenic effects, which can lead to diseases such as cancer [1, 4].

This thesis focuses on the effects of constitutively high concentrations of dNTPs due to misregulated RNR on the cell growth, proliferation, and survival in the Drosophila embryo by using RNR mutant D57N (RNR with a point mutation at the 57th position where an aspartate was replaced with an asparagine). We found that the mutant D57N embryos did not show an accumulation of DNA damage, nor did they have a significantly higher amount of nuclear fallout as compared to the wild type embryos. But, the D57N embryos did show much more cell death than the wild types. To resolve the tension created by the fact that D57N showed increased cell death but no DNA damage, we compared the activity of mitotic domain 11 and mitotic domain N to that in the WT embryos. The D57N embryo showed an excess of cells undergoing mitosis that were not within the boundaries of the domains established in the literature and wild type. Unclear as of yet, but it could be that the excess cells undergoing mitosis in the mitotic domains assay are the cells we see accumulated in the cell death assay. And lastly, though the mitotic domains patterning was not conserved, the Eve, Snail, and Twist patterns were conserved in the D57N mutant.