A humanised mouse cell

This image is by David Domínguez, a researcher from IMIM, and it shows a heterocarion, a fusion between a mouse and a human cell, dyed with three different colours. In the first image, in blue, we can see the DNA and the granular chromatin of the mouse nucleus, compared with the human. The second one, in green, shows the DNA which is replicating (both the murine and human), and in the last one we can visualise the cytoplasmic vesicles in red and the two nuclei in black.

The creation of heterocarions is used to study proteins that come in and out of the nucleus. In this case, mouse cells synchronised at the beginning of the cell cycle (G1 phase) were fused with human cells in S phase, during which DNA replication takes place. The mouse nucleus, in G1, does not have the factors needed for DNA duplication, but the human one, in S phase, does. After the fusion, these factors can travel from the human to the mouse nucleus, giving it the capacity to synthesize DNA, as we can see in the green image.