04.04.2013 Views

Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

7.3 Tumour Expression Correlation Results<br />

how each <strong>of</strong> these genes behaved in different settings: stem cell component<br />

<strong>of</strong> the tumour (GNS cells), primary tumour and lower grade gliomas, given<br />

they differ significantly from one another under a biological perspective. In<br />

fact, the tissues in the primary tumours comprise a heterogeneous mixture<br />

<strong>of</strong> cell types, whilst our GNS culture system has been designed to maintain<br />

the very specific stem cell component <strong>of</strong> the tumour in culture. Thus, we did<br />

not expect a perfect agreement between tissue and cell based results. Fur-<br />

thermore, assessing the behaviour <strong>of</strong> these same genes in lower grade gliomas<br />

could give us insights into the key players that determine the severity <strong>of</strong> the<br />

disease. Considering that our GNS cell lines have all been classified as primary<br />

GBMs, the differences observed from the lower grade glioma datasets will be<br />

especially meaningful in telling us how the same genes behave in the two dif-<br />

ferent categories (if we approximate that a significant percentage <strong>of</strong> the lower<br />

grade gliomas transform into higher grade gliomas such as GBMs).<br />

Panels a and c <strong>of</strong> figure 7.4 compare the GBM data in the TCGA dataset to<br />

the non-neoplastic brain tissue data in the TCGA dataset (altogether referred<br />

to as dataset GBM in Methods), for the core up-regulated (a) and core down-<br />

regulated (c) genes. Panels b and d, on the other hand, compare the GBM<br />

(grade IV glioma) data to the grade III glioma data in the combined Phillips<br />

and Freije datasets (altogether referred to as dataset HGG in Methods), for<br />

the core up-regulated (b) and core down-regulated (d) genes. From this figure<br />

we observe that there is a clear trend for the core up-regulated genes to be<br />

more highly expressed in glioblastoma tumours than in non-neoplastic brain<br />

tissue (Fig 7.4a; p = 0.02, randomisation test) and an opposite trend for the<br />

core down-regulated genes (Fig 7.4c; p = 3x10 -5 ). This means that, out <strong>of</strong> all<br />

the core differentially expressed genes that we measured with Tag-seq, a signif-<br />

icant part <strong>of</strong> the ones we found to be more highly expressed in GNS cell lines<br />

with respect to NS cell lines are also more highly expressed in primary GBM<br />

with respect to non-neoplastic brain tissue (histogram bars in the direction <strong>of</strong><br />

positive average log2(FC) identify these genes in panel a <strong>of</strong> figure 7.4).<br />

Similarly, a significant part <strong>of</strong> the core differentially expressed genes that we<br />

found to be down-regulated in our GNS cell lines with respect to our NS cell<br />

lines, are also down-regulated in primary GBM with respect to non-neoplastic<br />

brain tissue (histogram bars in the direction <strong>of</strong> negative average log2(FC) iden-<br />

tify these genes in panel c <strong>of</strong> figure 7.4). The colour <strong>of</strong> the histogram bars<br />

represents the level <strong>of</strong> significance <strong>of</strong> the comparison with black indicating a<br />

p-value0.01.<br />

171

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!