Glioblastoma (GB) is the most common and most aggressive brain tumor of primary central nervous system in humans. Treatment is unsuccessful due to the tumor's resistance to chemotherapy, radiotherapy and incomplete surgical removal. GB displays extensive cellular heterogeneity which represents a major obstacle for effective treatment. Cancer cells in a tumor are surrounded by a complex tumor microenvironment (TMO). Intercellular interactions within the TMO drive tumor progression. Glioblastoma stem cells (GMC) are resistant to therapy and protected in a special microenvironment - a niche. They coexist in the niche with non-cancerous stromal cells such as mesenchymal stem cells (MMC). We studied the impact of MMC on the proliferation and invasion of GMC in the zebrafish embryonic brain. We injected GMC and mixtures of GMC and MMC into the embryonic brain, which allowed us to compare tumors. The program ImageJ was used to quantify the relative difference of area and length of monoculture and coculture tumors in the brain in vivo. We developed and optimized a method of preparing zebrafish brain tissue sections, with injected labeled human cells, for immunohistochemistry. We used stem cell markers and markers of cancer cell invasion for interaction analysis. We found that GMC and MMC form mixed tumors in the zebrafish brain. We have shown that the presence of MMC does not alter proliferation, does not trigger differentiation, and does not alter invasion of GMC in the zebrafish brain. The presence of GMC increased the growth and invasion of MMC.
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