Monday, 5 May 2008

How Cells Communicate in Cell Division

Intricate network of regulatory functions explained Monday, 05 May 2008 A new study reveals how cells communicate to activate the cell division machinery. The finding made in the fruit fly may provide clues to address problems such as the proliferation of malignant cells and tumour growth in humans. The study was performed by researchers at the Institute for Research in Biomedicine (IRB Barcelona) on the fruit fly, Drosophila melanogaster, and unveils how distinct signalling pathways operate between neighbouring cells in order to activate the cell proliferation machinery that results in the organized growth of the fly wing. The signalling pathways involved in this process are also conserved in humans, and when altered in diverse tissues give rise to the appearance of different types of cancer, including cancer of the colon and skin, and leukaemia. The study has been undertaken in the Cell and Development Biology Laboratory headed by ICREA Research Professor Marco Milán, at IRB Barcelona, and has been released in and advanced online format by the EMBO Journal. The researchers have shown that the Notch and Wnt/Wingless signalling pathways exert control over the cell division machinery through two gene effectors, the proto-oncogene dMyc and the micro-RNA bantam. Regulated by Notch and Wnt/Wingless, these two genes instruct another gene, E2F, to activate the cell division machinery. “All the components were already known but we have clarified the order in the signalling cascade and the interaction between the molecular elements that regulate proliferation for the correct development of the wing”, explained Dr. Héctor Herranz, first author of the article. “Diseases like cancer cannot be understood without taking into account how the distinct molecular elements are integrated,” Prof. Milán said. Notch and Wnt/Wingless play a key role in embryo development, cell growth (proliferation) and the transformation of cells into specialized types (differentiation). The interesting feature is that these two pathways are highly conserved in humans and when mutations arise tumours appear. The fruit fly wing is a vital experimental model to find future biomedical applications. Prof. Milán goes on to say that “...this finding could provide clues about how to repress the cell proliferation signals in cancer”. The context is relevant Furthermore, the research has elucidated the relationship between Notch and Wnt/Wingless in the control of proliferation and the development of the fly wing. In fact, Notch has a repressor function, that is to say, when it is activated the cell division machinery is arrested. Only when Wnt/Wingless starts to work is Notch silenced, thereby triggering the cascade of genes that allow proliferation. “Notch works in this context as a tumour suppressor while Wnt/Wingless acts as an oncogene, that is, by cancelling the action of Notch it allows the cell division machinery to operate,” Prof. Milán explains. But the fundamental point for the researchers is that Notch and Wnt/Wingless can interchange their roles depending on the context in which they are operating because the true executors of the action are the genes that these proteins regulate, in this case dMyc and bantam. Researchers ask how, for example, in function of the tissue that is affected, Notch can serve as a “tumour suppressor” or as an oncogene. The conclusions drawn from this study, point to effectors being regulated by this pathway. “We have highlighted the importance of the context in which these signalling pathways work and that knowledge about the underlying regulatory elements is crucial to understand how a certain function is performed”, explains Dr. Herranz. According to Prof. Milán, diseases like cancer cannot be understood without taking into account how the distinct elements are integrated: that is to say, crosstalk between neighbouring cells, effector genes and cell cycle machinery. “Now we must look for similarities in vertebrates and humans to see whether these elements work in the same way in diseases”, he concludes. Reference: A Wingless and Notch double-repression mechanism regulates G1-S transition in the Drosophila wing. Héctor Herranz, Lidia Pérez, Francisco A. Martín, and Marco Milán The EMBO Journal, advance online publication 1 May 2008; doi: 10.1038/emboj.2008.84 ......... ZenMaster

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