Analyzing network formation during brain tumour initiation

High grade gliomas (HGGs) represent a complex and devastating disease and are posing an unmet clinical need. These tumours resist multi-modal therapies and survival times are only 14 months on average1. Recent studies show that glioma cells make neural network-like
connections with one another, and with host tissue2-4.

Tumour cells have been shown to be connected by long cellular processes called tumour microtubes. Tumour microtubes (TM) are crucial for the invasion and proliferation of glioma cells and connect single tumour cells to a functional communicating network, greatly enhancing its growth and drug-resistance.

The Sieger lab have developed a novel model to analyse glioma initiation stages in the larval zebrafish and were able to show that brain tumour initiating cells hijack mechanisms which are usually employed to direct microglial processes towards highly active neurons and injuries in the brain5. This aberrant role of microglia results in the active promotion of proliferation of early tumour cells. Interestingly, it is now clear that microglia play several roles in the formation of neural networks in the healthy brain, e.g. by promoting axonal growth, synapse formation and circuit function6-9. Measurements of Ca2+ transients revealed active signalling activity in these early tumour cells, implying functionality of these early networks. Importantly, we found that interfering with microglia activity resulted in impaired tumour microtube outgrowth as well as decreased Ca2+ signalling within the network.

My project will focus on the cellular networks built during HGGs formation. The principal long-term aims are:

1. To visually identify and characterise brain TMs in vivo using state-of-the-art microscopy;
2. To delineate the tumoral calcium networks established during the first phases of tumour formation, using calcium live imaging;
3. To investigate the role of microglia in the calcium signalling patterns of TM-positive fish, and their influence on tumour cells transcriptome.

The tumour initiation model I will use is based on overexpression of human oncogene AKT1 in zebrafish larvae, as this has previously shown to lead to glioma formation. The oncogene expression is linked to fluorescent labelling to allow for easy identification in vivo. Calcium imaging will be based on an already established mutagenic zebrafish line expressing the beta-actin:GCamp6f calcium reporter.


References:
1. Wen, P. Y. & Kesari, S. Malignant gliomas in adults. N. Engl. J. Med. 359, 492-507 (2008).
2. Osswald, M. et al. Brain tumour cells interconnect to a functional and resistant network. Nature 528, 93-98 (2015).
3. Venkatesh, H. S. et al. Electrical and synaptic integration of glioma into neural circuits. Nature 573, 1-27 (2019).
4. Venkataramani, V. et al. Glutamatergic synaptic input to glioma cells drives brain tumour progression. Nature 3, 147 (2019).
5. Chia, K., Keatinge, M., Mazzolini, J. & Sieger, D. Brain tumours repurpose endogenous neuron to microglia signalling mechanisms to promote their own proliferation. Elife 8, 19 (2019).
6. Miyamoto, A. et al. Microglia contact induces synapse formation in developing somatosensory cortex. Nature Communications 1-12 (2019).
7. Cunningham, C. L., Martinez-Cerdeno, V. & Noctor, S. C. Microglia Regulate the Number of Neural Precursor Cells in the Developing Cerebral Cortex. Journal of Neuroscience 33, 4216-4233 (2013).
8. Ueno, M. & Yamashita, T. Bidirectional tuning of microglia in the developing brain: from neurogenesis to neural circuit formation. Current Opinion in Neurobiology 27, 8- 15 (2014).
9. Mosser, C.-A., Baptista, S., Arnoux, I. & Audinat, E. Microglia in CNS development: Shaping the brain for the future. Progress in Neurobiology 149-150, 1-20 (2017).