Identifying a transcriptional program that regulates compensatory proliferation

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DESCRIPTION (provided by applicant): All animals undergo damage as they develop and age, and many organisms have evolved mechanisms to respond to and repair this damage. One such mechanism is compensatory proliferation, in which cells that are dying due to damage will mitogenically signal surrounding cells to increase proliferation and replace lost cells. This process is heavily utilized in damaged precursor cell populations during development and stem cells during adult life. However, many post-mitotic cells appear unable to re-enter the cell cycle and proliferate in response to damage, which hinders regeneration of adult tissues; the reasons for this inability are not known. In the eye precursor tissue of the fruit fly Drosophila melanogaster, there is a population of post-mitotic, undifferentiated cells that are able to undergo compensatory proliferation. How these cells are able to overcome negative cell cycle regulation and re-enter the cell cycle is currently unknown. Elucidating the genes involved in this process is important for understanding how to stop and perhaps reverse many of the phenotypes associated with aging. For example, tissues often accumulate damage with age as their regenerative abilities decrease. If the genes required for compensatory proliferation can be stimulated in these tissues, regeneration may be induced. Furthermore, damage often leads to inflammation and hyperproliferation, which contribute to disease development. Therefore, blocking genes involved in compensatory proliferation may prevent the accumulation of excess tissue and disease progression. This proposal aims to identify the genes involved in compensatory proliferation in the Drosophila post-mitotic eye precursor population, with the hypothesis that a unique transcriptional program is necessary for this process since a requirement for transcriptional regulation has already been shown. I will test this hypothesis by characterizing the transcriptional profile in these cells using fluorescence-activated cell sorting (FACS) to isolate the compensatory proliferating population and RNA-seq to identify the transcriptome. Genes that are highly expressed in these cells and not in their non-proliferating counterparts are likely to be involved in compensatory proliferation. In addition to providing candidate genes that may be required during compensatory proliferation, the results from these RNA-seq experiments will provide a hypothetical molecular network for compensatory proliferation. The second complementary approach will utilize RNAi to identify transcription factors required for compensatory proliferation. We will identify these necessary genes by individually knocking down expression of all Drosophila transcription factors, the majority of which have vertebrate homologs; genes that are required for compensatory proliferation in developing eyes subjected to damage will produce rough, small adult eyes due to a decrease in the number of cells present. Any additional candidates from the RNA-seq experiments will also be tested using this assay. Further genetic and molecular analysis will be performed to characterize the interactions between multiple pathways. The results from these experiments will provide a comprehensive view of compensatory proliferation and will provide candidate genes that may be involved in regeneration and disease in vertebrates.