During mitosis cells must segregate the replicated copies of their genome to their daughter cells with extremely high fidelity. Segregation errors lead to an abnormal chromosome number (aneuploidy), which typically results in disease or death. A number of mechanisms are employed by cells to ensure that mitosis is error-free, and one of the most important of these is the spindle checkpoint. This checkpoint acts as a mitotic surveillance system, and monitors the interaction between chromosomes and the mitotic spindle. Only when all chromosomes are attached to spindle microtubules in a bi-polar manner, with each pair of sister-chromatids attached to opposite spindle poles, is anaphase allowed to proceed. Through our studies we aim to understand what checkpoint components sense at kinetochores (is it simply lack of attachment or also lack of tension?), and how the checkpoint (Mad and Bub) proteins act to inhibit Cdc20-APC/C activity and thereby delay the onset of anaphase.
The Mad and Bub proteins are essential in vertebrates: in their absence every mitosis is too short and massive chromosome segregation errors occur, leading to apoptosis. Abnormal expression, or mutation, of Mad and Bub proteins can give rise to aneuploidy and are implicated in cancer progression.
We now focus on the fungal pathogen Cryptococcus neoformans in our studies of mitosis and spindle checkpoint mechanism. Amongst other exciting projects, we currently work on:
a) structure-function analysis of the Mad and Bub proteins in Cryptococcus.
b) identification of the key substrates of the Mps1, Bub1, Polo and Aurora kinases.
c) identification and analysis of checkpoint silencing mechanisms. How does protein phosphatase (PP1 and PP2A) activity aid anaphase onset once the checkpoint is satisfied?
d) further developing synthetic biology approaches to induce and regulate artificial checkpoint arrest in Cryptococcal cells. See:
Generation of a Spindle Checkpoint Arrest from Synthetic Signaling Assemblies
e) analysing ploidy control and aneuploidy in Cryptococcus neoformans. Studying the consequences of prolonged mitotic arrest in this fungal pathogen.