Unlocking the molecular and cellular mechanisms regulated by the ribonuclease Dis3L2 in Drosophila and human cell proliferation.

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Development of a single egg cell into a complex multicellular organism requires exquisite control of cell proliferation. Regulation of cell proliferation is not only important during development but also required in regeneration and repair of damaged tissues and also during wound healing. Co-ordination of tissue growth is also crucial to maintain the correct size and shape of different organs. Similarly, controlled proliferation is important in evolution where growth of certain areas of the body (e.g the brain) may be favoured by natural selection. However, uncontrolled cell proliferation is a hallmark of cancer with many genes involved in growth and proliferation implicated in cancer progression. Although the pathways involved in uncontrolled cell proliferation as occurs in cancer are well known, the pathways governing normal, co-ordinated cell proliferation have not been as well studied.Using human kidney cells as well as the fruit fly Drosophila we have recently discovered that cell proliferation can be regulated by a protein named Dis3L2. Depletion or removal of this protein results in excess proliferation. These results are relevant to human disease as DIS3L2 has been shown to be mutated in an overgrowth syndrome (Perlman syndrome) where affected children are larger than normal, have abnormal enlargement of organs (e.g. kidneys) and susceptibility to Wilms' tumour (a kidney cancer). In addition, up to 30% of sporadic Wilms' tumours have mutations in Dis3L2. Interestingly, Dis3L2 has also been implicated in body weight and height variation in indigenous Ethiopian sheep, suggesting selection in our domestic animals. Therefore, understanding the molecular mechanisms whereby Dis3L2 exerts its effects on tissue growth is likely to be relevant in normal growth as well as human overgrowth diseases.Dis3L2 is an enzyme known to "chew up" and destroy mRNA molecules which instruct the cell to make particular proteins. This enzyme is remarkable in that it has a similar structure and function in a wide range of organisms, from bacteria through to humans. Using state-of-the-art molecular methods in fruit flies, we have discovered that Dis3L2 targets a small subset of mRNAs, including an mRNA encoding a growth factor named 'imaginal disc growth factor 2' (idgf2). Idgf2 has been previously shown to cause proliferation of fruit fly cells via an unknown pathway. For human kidney cells in culture, we have discovered that depletion of DIS3L2 results in enhanced proliferation, and that this involves a well known cellular pathway. We do not yet know the mRNA targets of DIS3L2 which activate this proliferation pathway in humans. These results are novel in that no other research group as yet has unravelled the cellular mechanisms linking DIS3L2 with cell proliferation. The specific aims of this project are to understand the pathways and cellular mechanisms whereby Dis3L2 controls cell proliferation in Drosophila and in human kidney cells. We will use modern molecular and cell biological methods (such as CRISPR-Cas9 for gene editing) to dissect this proliferation pathway and identify key components. In fruit flies, we think that Dis3L2 directly targets idgf2 after it has been "tagged" for degradation by other cellular factors. We predict that Idgf2 then activates a specific cellular enhance cell proliferation. In humans, we predict that DIS3L2 targets another growth factor which in turn activates the same pathway to promote proliferation. We have the expertise, as well as the molecular and genetic tools to test these ideas. The knowledge gained during this project may facilitate treatments for cancer as well as help us to understand the ways that normal tissues grow and develop. This project will therefore provide valuable insights into a new way of regulating cell proliferation which can be used in the development of new therapeutics.