Research

Investigating a new mechanism for genome maintenance that processes DNA bridges during cytokinesis using C. elegans and cultured mammalian cells.

Faithful chromosome segregation requires the removal of all DNA bridges that physically link chromatids before the completion of cell division. Failure to do so can prevent cell division, thereby leading to polyploidization or can lead to the severing of chromosomes if the cell divides. These DNA bridges can originate from persistent recombination intermediates, local under-replication, and chromosome entanglement. While several redundant safeguard mechanisms to process these DNA bridges exist throughout the cell cycle (from G2 to anaphase), some bridges often persist into late mitosis. However, very little is known about how these persistent DNA bridges are resolved. Our working hypothesis is that the LEM-3 nuclease in Caenorhabiditis elegans and its human ortholog ANKLE1 are part of a 'last chance' mechanism that resolves these remaining DNA bridges just before the cell divides (Figure 1).

Building up on previous work from the Gartner lab (PMID: 29463814), we are investigating the mechanistic details of this pathway and how it is coordinated with cell cycle progression. That end, we are using C. elegans and human cells and a combination of cell biological, biochemical, genetic and proteomic approaches.

Studying such mechanisms is important as failure to process DNA bridges leads to aneuploidy, micronuclei formation and cytokinesis failure, which are phenotypes associated with cancer progression. Furthermore, a region of human chromosome 19p13.1, narrowed down to the ANKLE1 locus, has been associated with increased susceptibility to breast and ovarian cancer (PMID: 27601076). Finally, SNP in the ANKLE1 locus leading to reduced ANKLE1 expression have also been recently associated with increased risk of colorectal cancer (PMID: 31509622). Thus, our studies will therefore not only increase our understanding of the mechanisms by which cells maintain their genome integrity during mitosis but has also the potential to provide insight into the suspected role of ANKLE1 in the development of these cancers.

Investigating the mechanism by which mitochondrial genome integrity is maintained in response to oxidative stress.

Mitochondria, the well-known powerhouse of the cell, have their own genome of ~17kb, which codes for 22 tRNAs, 2 rRNA and 13 essential proteins of the electron transport chain. Because of its proximity to the electron transport chain, the mitochondrial genome is exposed to high levels of reactive oxygen species (ROS), resulting in high level of oxidative DNA damage and a mutational rate ~15-fold higher than the one of nuclear DNA.

Base Excision Repair (BER) is involved in the repair of various DNA damages affecting the nuclear genome, including oxidized bases. More recently, BER has been shown to be also involved in the repair of mitochondrial DNA oxidized bases. Interestingly, the same proteins participate in nuclear and mitochondrial BER. It remains however unclear how cells decide whether these proteins translocate to the mitochondria or to the nucleus.

Using C. elegans and human cells, our main goal is to discover the signaling pathway that leads to the translocation of BER proteins into mitochondria specifically in response to mitochondrial DNA damage.(Figure 2).