Characterization of the Role of Mcm10 in DNA Replication in Drosophila melanogaster

Abstract

Replication of the genome and proper formation, and packaging, of chromatin are processes essential to eukaryotic life. Maintenance of epigenetic chromatin states is essential for faithfully reproducing the transcriptional state of the cell; likewise, replication of DNA with high fidelity is crucial for accurate passage of genetic information from a cell to its progeny. Defects in DNA replication and improper regulation of the chromatin states can result in genome instability which can manifest as disease, or death of the organism. There are a plethora of factors involved in the process of DNA replication in eukaryotes, and recent studies have shed light on one of the factors called mini-chromosome maintenance 10 (Mcm10) as an essential DNA replication factor. First discovered in S. cerevisiae, Mcm10 is an abundant nuclear protein that has been implicated in the activation of the Pre-RC, interacts with members of the elongation machinery such as Pol[alpha], and has recently been shown to be required in the formation of heterochromatin in both yeast and Drosophila. Previous analysis of two Drosophila Mcm10 mutant alleles demonstrated that Mcm10 not only plays a role in DNA replication, but also has a role in heterochromatic silencing and chromosome condensation. With Drosophila melanogaster as a model we further investigated the roles of Mcm10 by using a collection of over 20 missense mutations generated via a Tilling approach. Mitotic index data generated using brain cells of these mutant strains showed no delays in progression through M-phase of the cell cycle. Interestingly though, several aberrant chromosomal phenotypes such as condensation defects, aneuploidy, anaphase bridge defects, separated sister chromatids and chromosome breaks, were observed in varying frequencies suggesting that Mcm10 is involved in maintaining genomic stability. Additionally, the Mcm10 mutant strains showed defects in endoreplication and packaging of DNA within the nuclei of salivary glands. By understanding the various roles of Mcm10 we can help elucidate the biological functions of this well conserved protein as well as provide information on the domains of the protein required for its different biological functions.