Cell Division & Genomic Stability

ABOUT

Our group was formed almost 30 years ago by Claudio Sunkel who carried out an extensive gene discovery program aimed to understand the fundamental mechanisms that ensure the fidelity of chromosome segregation during cell division. Using Drosophila, we identified, a number of conserved and essential genes required for the regulation of mitotic progression including the first POLO–like kinase. Subsequently, the group was involved in the genetic characterization of proteins involved in chromosome structure and of components of the Spindle Assembly Checkpoint that monitors Kinetochore-Microtubule interactions. We are currently organized into two lines of research, each headed by independently funded PIs:

 

Claudio Sunkel (Co-PI Pedro Resende and Antonio Pombinho) - Aneuploidy and tumorigenesis/drug screening.

We are developing tumor models in Drosophila caused by deregulation of chromosome segregation. We want to understand the molecular events that take place in tumor formation and relate those to conserved pathways in human cancer cells. This project aims to study the impact of aneuploidy in adult stem cell behavior and determine its relationship with tumorigenesis. Furthermore, this research line aims to carry out a drug discovery program that is using human tissue culture cells to identify compounds that interfere with the Spindle Assembly Checkpoint (SAC). The objective is to develop compounds that could target SAC-competent tumor cells. 

 

Carlos Conde – Uncovering the molecular mechanisms that control and monitor the interaction of chromosomes with spindle microtubules

The fidelity of chromosome segregation relies on the attachment of sister kinetochores to microtubules of opposite spindle poles and on the Spindle Assembly Checkpoint (SAC), a biochemical pathway that prevents anaphase onset until the former state is achieved. Mitotic kinases are key regulators of both processes, which are frequently deregulated in malignant cells. Our team combines Drosophila genetics, human cultured cells, high-resolution imaging and biochemical approaches to provide a detailed understanding of the mechanisms orchestrating kinetochore-microtubules interactions and SAC signaling.  We aim to unveil the molecular and mechanical switches that fine-tune the action of key mitotic kinases at kinetochores and how these are relayed to microtubule attachment regulation and translated into biochemical signals that control SAC activity. Our findings generate critical knowledge to understand how dividing cells prevent aneuploidy.

 

RESEARCH

Claudio Sunkel

Our main objective has been to identify and characterize the molecular mechanisms involved in faithful chromosome segregation during mitosis. Our major contribution to the field was the cloning and characterization of the Polo-like kinase family of mitotic regulators. We demonstrated that Polo is required for centrosome organization and function, for regulation of the spindle and in kinetochore assembly. Later we identified and characterized the CLASP family of microtubule regulators and demonstrated their role in mitosis. More recently, we have devoted our attention to the Spindle Assembly Checkpoint that monitors microtubule-kinetochore attachment and chromosome segregation. We characterized the role of Mad2, BubR1, Bub3 and Mps1 in this process and integrated our results into a molecular pathway that also involves Aurora B and Polo. We have studied the molecules involved in mitotic chromosome structure and analyzed the role of condensins showing for the first time their essential role in sister chromatid resolution prior to anaphase onset.  We also localized for the first time the cohesion subunit DRAD21 to the centromere of mitotic chromosomes.

 

Carlos Conde

Our research in the field of mitosis has been focused on SAC signalling and its regulation by mitotic kinases. My team undertook a comprehensive dissection of the hierarchical framework controlling SAC function in Drosophila and found that Polo kinase lies upstream of the pathway promoting Mps1 activation at unattached kinetochores. Our findings also showed that active Mps1 promotes BubR1 phosphorylation to generate the 3F3/2 phosphoepitope at tensionless kinetochores. Furthermore, we were able to uncouple for the first time, 3F3/2 levels from inter-kinetochore tension, which helped us to show that the molecular outcome of 3F3/2 formation is to promote the association of Cdc20 with BubR1 to allow proper kinetochore recruitment of Cdc20 and MCC assembly required for a sustained SAC response.

Drosophila cell undergoing final stages of mitosis after DNA (Blue) separation in telophase showing the spindle microtubule (green) and the microtubule associated protein (Red) at the central spindle and also ate the spindle poles. MAST was the founding member of the CLASP protein family of microtubule regulators conserved in all eukaryotes.