###image### ###groupLeadInfo###

###office_address### ###buildings######office_roomnumber### ###office_phone### ###email### ###url### ###leadCvLink###

Administrative Assistant

Nadine Iberl
Biozentrum, Room 709
Phone: +41 61 207 20 66
Fax: +41 61 207 20 78
Email: nadine.iberl-at-unibas.ch

A STIL truncation (Val1219X) resists proteasomal degradation at mitotic exit.

Monitoring STIL expression for a whole cell cycle.

Research group Erich Nigg

Control of chromosome segregation and centrosome duplication in human cells

Fig. 1: A dividing human cell was stained with antibodies against tubulin (green) and a kinetochore marker (red); condensed chromosomes are visualized by staining with DAPI (4',6-diamidino-2-phenylindole; blue). Size bar: 5 ?m.

Cell proliferation depends on passage of cells through a series of biochemical reactions that are collectively termed 'cell cycle'. This fundamental process is indispensable for the development of an entire organism from a single cell (fertilized egg), as well as the constant renewal of most cells throughout adult life. Key events during cell cycle progression include the duplication of the chromosomes (the genome) and their subsequent segregation to two nascent daughter cells. Chromosome segregation occurs during a cell cycle phase known as 'mitosis', a highly dynamic and spectacular stage of the cell cycle (Figure 1). The main goal of our research is to elucidate the mechanisms that regulate mitosis in time and space and thereby ensure the error-free segregation of chromosomes. A better understanding of mitosis will hopefully illuminate the origins of the chromosome aberrations (aneuploidies) that give rise to birth defects and constitute hallmarks of aggressive human tumors.

Central to mitosis is the spindle apparatus, a complex and highly dynamic microtubule-based structure that captures chromosomes through specialized protein structures termed kinetochores (Figure 2). Hence, we study the composition, regulation and dynamics of the mitotic spindle and kinetochores. In addition, we aim at elucidating the function of a surveillance mechanism - the spindle assembly checkpoint - that monitors the complete attachment of all mitotic chromosomes to the spindle.

At the two poles of the spindle apparatus are tiny organelles known as 'centrosomes' (Figure 3). The biogenesis, duplication and function of centrosomes (and their constituent centrioles) constitute a second major research focus of our laboratory. Centrosomes function to organize microtubule arrays in most animal cells and are present as only one or two copies per cell, depending on cell cycle stage. At the core of each centrosome are two microtubule-based cylindrical structures called 'centrioles', embedded in a matrix of pericentriolar proteins. Deregulation of the centrosome/centriole duplication cycle is believed to constitute a major cause of chromosome mis-segregation during the development of human cancers. Furthermore, certain brain diseases (notably microcephaly) and some forms of dwarfism have been causally linked to mutations in specific centrosomal proteins. Importantly, centrioles function also as basal bodies for the formation of cilia and flagella in quiescent cells, and mutations in genes coding for centriole/basal body proteins contribute to a multitude of diseases and syndromes (ciliopathies) that reflect the absence or malfunction of the basal-body/ciliary apparatus.

Fig. 2: A cultured human cell was stained with antibodies against two kinetochore components, Mad1 (green) and Mad2 (red); DNA was stained by the dye DAPI (4',6-diamidino-2-phenylindole; blue). Also visible is the nuclear envelope (stained by anti-Mad1 antibodies, green). Size bar: 5 ?m.

Our laboratory combines reverse genetics (e.g. RNA interference), immunocytochemistry (including structured illumination super-resolution microscopy) and multiple biochemical techniques (notably mass spectrometry) to unravel the molecular mechanisms that ensure correct centrosome duplication and chromosome segregation in human cells. Many of our studies focus on phosphorylation (a reversible protein modification controlled by kinases and phosphatases). Studying mostly human cells in culture, we have used mass spectrometry to establish inventories of proteins and phosphorylation sites in the spindle apparatus, the kinetochore and the centrosome. More recently, we focus on the wiring of key regulatory circuits, as defined by kinases, phosphatases, and selected substrates. We anticipate that our work will lead to a better understanding of the regulation of chromosome segregation and centrosome duplication in normal cells, as well as provide insights into the deregulation of these processes in disease.

In the recent past, we have discovered and characterized several novel spindle components and proteins implicated in centriole duplication. Of particular interest is our discovery of Plk4 as a key regulator of centriole biogenesis and the demonstration that a ternary complex of Ska proteins (Ska1, 2 and 3) plays a major role in stabilizing the attachment of spindle microtubules to kinetochores. Ongoing work concerns the function and regulation of several cell cycle-regulatory kinases, including Polo-like kinases (notably Plk1 and Plk4), Aurora kinases and spindle checkpoint kinases (Mps1 and Bub1).

Fig. 3: Centrosomes organize microtubule arrays. A cultured human cell was co-stained with antibodies against the protein kinase Plk4, a key regulator of centriole duplication (green), and antibodies against the cytoskeletal component tubulin (red). Size bar: 5 ?m.

One major challenge in contemporary biological and biomedical research concerns the development of technologies that will permit the acquisition of quantitative information about the abundance, localization and dynamics of proteins and protein modifications under physiological conditions. We anticipate that such technologies will become increasingly important not only in systems biology but in life science research altogether. Hence, we have optimized mass-spectrometry based procedures (selected reaction monitoring) that allow us to monitor, in quantitative terms, the abundance of key components involved in both centrosome duplication and chromosome segregation. In parallel, we have begun to use somatic gene targeting approaches that should allow us to visualize and quantify a subset of these very same components in time and space.

The cell cycle field holds considerable promise for the development of novel therapeutic approaches. In particular, it appears legitimate to hope that new information on the mechanisms that govern chromosome segregation and cell division will contribute to the design of novel strategies to thwart cancer growth. This has been widely recognized not only in Academia, but also in the Pharmaceutical and Biotechnology industry, providing ample opportunities for collaboration and translational research.