Maki Asano , MD, PhD
Assistant Research Professor

My laboratory studies cell cycle regulation. This fundamental biological process is vital for homeostasis and development of every organism. Failure to accurately regulate the cell cycle leads to serious consequences including cancer, birth defects or fetal death.

To elucidate the mechanisms underlying cell cycle control, we use a combination of molecular biology, genetics, biochemistry and cell biology. As a model system, we use the fruit fly, Drosophila melanogaster. The cell cycle machinery is broadly conserved among eukaryotes, and so our experiments using the genetically tractable fruit fly will offer insight into the workings of the human cell cycle.

Research interests and projects

Biological function of ORC1

We have been working on ORC1 (Origin Recognition Complex subunit 1), identified an essential protein for the initiation of DNA replication in yeast. Over-expression of ORC1 can induce ectopic DNA replication in some cell types in flies demonstrating that the level of this protein can limit the initiation of DNA synthesis.

Projects regarding this aspect are:

Loss-of-function analysis of ORC1. We prepared an orc1- mutant by homologous recombination. We are currently using this mutant to investigate the role of ORC1 in different types of DNA replication (proliferative, endo-replication, and gene amplification). We also are looking into the phenotypes outside of DNA replication such as in position effect variegation (PEV), development and differentiation.

Identify functional domains of ORC1. To identify the functional domain(s) for each role played by ORC1, we will express ORC1 derivatives bearing various deletion or point mutation in the orc1-mutant background and examine which part(s) of ORC1 is required to compensate each of the orc1- phenotypes.

Identify ORC1-associated proteins. ORC1 presumably associates with many different partners during DNA replication, PEV, etc. To identify these partners, we will affinity purify ORC1-associated proteins, by expressing a tagged version of ORC1 in vivo. We will look for tissue-specific and developmental-stage-specific partners of ORC1.

Cell cycle-regulated degradation of ORC1

Unlike ORC1 in budding yeast, we showed that ORC1 levels in Drosophila fluctuate during cell cycle progression. Subsequent work from the Stillman lab demonstrated that the level of human ORC1 also fluctuates throughout the cell cycle. Drosophila ORC1 is degraded by the Anaphase Promoting Complex (APC) via a novel motif that we named the ORC1 destruction box (O-box).

Projects regarding this aspect are:

Characterization of the O-box. We are currently better defining the O-box to understand why it is specifically targeted by Fzr/Cdh1 and not Fzy/Cdc20. We will also investigate whether phosphorylation plays a role in O-box-mediated degradation.

Identify new O-box proteins. Better definition of the O-box will also allow us to identify new APC targets using the O-box as a tool. Investigating these proteins will deepen our understanding of cell cycle regulation.

Role of Cdc6

Recently, we have begun to investigate the activity of Cdc6, another essential replication protein.

Regulation of Cdc6 in vivo. We are studying both the transcriptional and post-translational regulation of Cdc6 during cell cycle progression and development, with a particular focus on the role of regulated proteolysis.

Gain-of-function analysis. We have over-expressed Cdc6 in various cell types at different stages of development and are currently analyzing the resulting organismal and cellular phenotypes.

Loss-of-function analysis. We will produce a cdc6-mutant by homologous recombination and characterize the resulting phenotypes.