Centriolar satellites are acentriolar assemblies of centrosomal proteins (June 2019)
Click here to access the original paper in the EMBO Journal by Valentina Quarantotti et al. Jia-Xuan (aka Jimmy) Chen from the Miller lab (and now at IMB, Meinz) was instrumental to our data analysis.
Centriolar satellites are cytoplasmic membraneless granules implicated in centrosome and primary cilia function. Although several satellite components have been identified previously, a comprehensive survey of satellite content was lacking. We performed proteomic profiling of satellites and revealed over 200 satellite-associating proteins including structural and regulatory components. Our data reveals a substantial overlap with the centrosome proteome both in normal and acentriolar cells. In fact, we have identified over half of all known centrosomal proteins in these structures.
Specificity of RNAi, LNA and CRISPRi as loss-of-function methods in transcriptional analysis (July 2018)
Click here to access the original paper in Nucleic Acid Research by Lovorka Stojic and Aaron Lun et al. This work has resulted from our longstanding collaboration with the Marioni and Odom labs at CRUK CI.
Disease-associated mutations in CEP120 destabilize the protein and impair ciliogenesis (May 2018)
Ciliopathies are a group of genetic disorders caused by a failure to form functional cilia. Due to a lack of structural information it is currently poorly understood how ciliopathic mutations affect protein functionality to give rise to the underlying disease. Using X-ray crystallography the van Breugel lab showed that the ciliopathy-associated centriolar protein CEP120 contains three C2 domains. The point mutations V194A and A199P, which cause Joubert syndrome (JS) and Jeune asphyxiating thoracic dystrophy (JATD), respectively, both reduce the thermo-stability of the second C2 domain by targeting residues that point towards its hydrophobic core. By genome engineering cells to contain these exact mutations, Nimesh found that both mutations caused a reduction in CEP120 protein levels. Although the mutant versions of CEP120 still supported centriole duplication, they compromised the recruitment of distal centriole markers and cilia formation. Our results provide insights into the disease mechanism of two ciliopathic mutations in CEP120, identify putative binding partners of CEP120 C2B and suggest a complex genotype-phenotype relation of the CEP120 ciliopathy alleles.
New molecular insights into why neural stem cells are sensitive to Zika infection (July 2017)
Click here to access the original paper in Science by Pavithra Chavali, Lovorka Stojic et al.
It takes the coordinated action of many genes to grow a healthy human brain with much of the responsibility lying with stem cells of the developing nervous system. Inherited mutations in genes that lead to loss of these cells cause a rare human genetic condition that manifests in small brain or microcephaly. The recent Zika virus outbreak in Brazil coincided with a massive increase in babies born with microcephaly, but why Zika virus preferentially targets the brain stem cell population has remained a mystery.
In this new study we find that similarly to their rodent counterparts human brain stem cells rely on a gene product called Musashi-1 to supply the large numbers of neurons required for normal brain growth. Indeed, children who carry a mutated form of Musashi-1 have a form of inherited microcephaly. Understandably, brain stem cells produce large quantities of Musashi-1 to sustain their normal developmental program. However, when it comes to infection by Zika virus, we have discovered that Musashi-1 turns into the Achilles’ heel of this cell population. In fact, Zika virus replicates much faster in cells that contain Musashi-1 than in those lacking this gene product. Rapid viral replication leads to virus overload of cells, often culminating in their death. Zika therefore preferentially kills cells with high Musashi-1 levels, which in the human embryo correspond to neural stem cells. This is bad enough, but the story has an additional twist.
We have also found that Musashi-1 protein binds the genome of the Zika virus, and the virus essentially prevents Musashi-1 from performing its normal cellular roles. As a result, even if a brain stem cell does not die of the infection, by using Musashi-1 for its own purpose, the virus will interfere with the normal developmental program of these cells, leading to a reduction in neurons produced and microcephaly.
Holding it all together at the centrosome-spindle pole interface
Click here to access the original paper in Nature Communications by Pavithra Chavali et al.
For organisms to survive, their cells need to be continuously replenished through cell divisions. It is crucial that cells pass on a complete set of genes every time they divide. This is achieved by the faithful replication of our chromosomes, followed by their equal segregation between daughter cells. Chromosomes are anchored to and distributed by the mitotic spindle, a symmetric bipolar structure, composed of protein fibres called microtubules. The poles of the spindle are formed by centrosomes, specialised organelles that produce microtubules. It is therefore vital that cells contain precisely two centrosomes when undergoing cell division, or else the bipolar nature of the mitotic spindle is compromised.
Interestingly, cancer cells have been shown to harbour multiple centrosomes. Therefore they require a special mechanism called centrosome clustering by which multiple centrosomes form two clusters, each of which associates with a spindle pole. This adaptation makes sure that cancer cells divide and survive despite having extra centrosomes. In the recent years, several screens have identified key genes that play a role in centrosome clustering, making them attractive therapeutic targets.
We report that CEP215, a core centrosomal protein, interacts with HSET, a motor protein implicated in centrosome clustering. By mapping the binding interface in these proteins, we were able to show that this complex was required to tether centrosomes at spindle poles in normal cells. In addition, disruption of the CEP215-HSET protein complex precluded centrosome clustering and cancer cell survival. We have therefore identified a centrosomal protein complex that aids centrosome clustering and also help to anchor centrosomes at spindle poles in normal cell divisions. During evolution centrosomes have adopted a tight association with spindle poles; this very ability appears to be exploited for centrosome clustering by cancer cells containing supernumerary centrosomes.
This research will contribute to the understanding of how cells cluster extra centrosomes and guide the development of potential drugs that target this function of HSET.
The project was funded by Cancer Research UK.