Characterization of mechanisms regulating de-differentiation and the re-acquisition of stem cell identity

Characterization of mechanisms regulating de-differentiation and the re-acquisition of stem cell identity

Funding Type: 
New Faculty I
Grant Number: 
RN1-00544-B
Award Value: 
$382,773
Disease Focus: 
Aging
Stem Cell Use: 
Embryonic Stem Cell
Status: 
Active
Public Abstract: 
Stem cells are the building blocks during development of organisms as varied as plants and humans. In addition, adult or “tissue” stem cells provide for the maintenance and regeneration of tissues, such as blood and skin throughout the lifetime of an individual. The ability of stem cells to contribute to these processes depends on their unique ability to divide and generate both new stem cells (self-renewal) as well as specialized cell types (differentiation). In some tissues, cells that have already begun to specialize can revert or “de-differentiate” and assume stem cell properties, including the ability to self-renew. De-differentiation of specialized cells could provide a “reservoir” of cells that could act to replace stem cells lost due to wounding or aging. This proposal seeks to uncover the mechanisms that are utilized to regulate the process of de-differentiation and to compare these to the mechanisms that endow stem cells with the ability to self-renew. A thorough understanding of the factors that regulate self-renewal programs will be essential for the expansion and long-term maintenance of adult stem cells in culture, a necessary step towards the successful use of stem cells in regenerative medicine and tissue replacement therapies. Furthermore, understanding the mechanisms by which partially differentiated cells can reacquire self-renewal potential and how these programs are utilized during the normal course of tissue maintenance and repair could provide powerful strategies for regenerative medicine by stimulating inherent self-repair programs normally present within tissues and organs.
Statement of Benefit to California: 
We plan to identify and characterize genes and proteins that are involved in regulating the ability of specialized cell types to revert back into a more immature cell that can act like a stem cell. Information revealed by these experiments will likely prove useful in understanding both how tissues can be maintained during aging and/or repaired after damage. Subsequently, this knowledge could be developed into powerful strategies for regenerative medicine by stimulating inherent self-repair programs normally present within tissues and organs. In addition, these experiments may provide some insight into how some tumors may be initiated, leading to cancer. Lastly, in the course of these studies, we will be generating ES cell-like cells from spermatogonial stem cells. Although we will initially work with mouse tissues, our ultimate goal would be to adapt these techniques to human spermatogonial stem cells, which would then be used as a source for generating human ES cells. We would make these cells readily available to other investigators and companies in hopes of accelerating the pace of discovery.
Progress Report: 

Year 1

Stem cells are the building blocks during development of organisms as varied as plants and humans. In addition, adult or “tissue” stem cells provide for the maintenance and regeneration of tissues, such as blood and skin throughout the lifetime of an individual. The ability of stem cells to contribute to these processes depends on their unique ability to divide and generate both new stem cells (self-renewal) as well as specialized cell types (differentiation). In some tissues, cells that have already begun to specialize can revert or “de-differentiate” and assume stem cell properties, including the ability to self-renew. De-differentiation of specialized cells could provide a “reservoir” of cells that could act to replace stem cells lost due to wounding or aging. This proposal seeks to uncover the mechanisms that are utilized to regulate the process of de-differentiation and to compare these to the mechanisms that endow stem cells with the ability to self-renew using the fruit fly Drosophila melanogaster as well as pluripotent human cells. In the most recent funding period, we have found that the multiple sex combs (msx) gene in fruit flies encodes a protein that is important for balancing the number of proteins that control DNA packaging. Our research has shown that when a subset of these proteins is present in excess, it causes a low level DNA damage response. In return, it appears that another group of proteins that regulate self-renewal and differentiation are recruited away from their ‘normal’ job and used for DNA repair. As many chemotherapeutic agents and anti-cancer strategies involved using DNA damage to kill proliferating cells, our data suggest that not only will stem cell be susceptible to killing, but the normal differentiation programs might also be affected. Because the function of this gene is conserved in human cells, we speculate that understanding the function of this gene will provide insight In addition, we have continued to characterize the role of human Igf-II mRNA binding protein 1 (hIMP1) in pluripotent human cells and during early neural differentiation. Our primary progress in the current funding period was to identify genome-wide RNA targets for hIMP1, hIMP2, and LIN28 (a protein that associates with IMP proteins). Lastly, we have published a manuscript that shows that specialized stem cell microenvironments (also known as ‘niches’) are able to sustain similar numbers of stem cells, despite damage. This compensatory behavior is important because it suggests that the niche is an important component in sustaining stem cells after tissue damage or during wound repair. We will now use this observation as the basis for a screen to identify additional genes and pathways that regulate maintenance and regeneration of stem cell niches in more complex mammalian tissues.

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