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Daniel Kilpatrick, Ph.D.Academic Role: Associate Professor
Faculty Appointment(s) In:
Other Affiliation(s):
Transcriptional Control of Neurogenesis
Figure 1. Regulation of E2F and Rb family members during neuronal differentiation of PC12 cells (top). Functional effects of E2F4 induction on the initiation and maintenance of PC12 cell differentiation (bottom). We have begun to explore this question by examining the role of a family of transcription factors termed E2Fs. These factors play a critical role during the cell cycle by regulating the expression of genes required for DNA synthesis and cycle progression. Further, they are thought to be important for growth arrest and differentiation, although proof of such a role has been lacking. We have now shown that this family of factors is differentially regulated during neuronal differentiation, both in cell lines and in vivo (Persengiev, 1997). In particular, E2F4 is highly upregulated while other E2Fs are generally downregulated (Figure 1.) Further, using a tetracycline-regulation system, we have demonstrated that E2F4 actively promotes both the establishment as well as the maintenance of the neuronal phenotype (Persengiev, 1998)(Figure 1.) We are exploring how this factor functions to promote neuronal differentiation, including its protein interactions during this process, as well as studying its functional role in vivo using transgenic mice. Regulation of the Neurotrophin Receptor, TrkA, in Neurons and Neuroblastoma CellsDuring neuronal development, neurotrophic factors have a pivotal role in the organization of the nervous system by selecting which neurons will survive and terminally differentiate. These effects are mediated by specific neurotrophin receptors termed Trks. One of these, TrkA, serves as the receptor for nerve growth factor and is required for normal development of the peripheral nervous system as well as the function of central forebrain neurons. We are interested in understanding how the TrkA gene is regulated for several reasons. For one, based on its intimate involvement in terminal differentiation of peripheral neurons, TrkA regulation should shed light on the mechanisms controlling this final phase of neuronal differentiation. Further, TrkA expression is positively correlated with a favorable prognosis in neuroblastoma, a mainly childhood form of cancer originating within the sympathoadrenal system that is typically malignant. This correlation may reflect an active role for TrkA in promoting tumor growth arrest and/or may be an indication of a more differentiated state of the tumor cells. In either case, elucidating the determinants of TrkA expression in neuroblastoma cells may ultimately lead to a more intelligent design of chemotherapeutic strategies for converting high-stage, TrkA-negative tumors into more favorable ones. We have demonstrated that variable expression of the TrkA gene is controlled primarily at the level of gene transcription. Based on this, we have begun to characterize the human TrkA promoter in neuroblastoma cell lines exhibiting high and low expression of this gene as well as in non-expressing cell lines. This has led to the identification of a 140-bp promoter segment adjacent to the initiation region that is important for cell-specific promoter regulation and elevated activity in high-expressing cell lines (Chang, 1998) (Figure 2). This region also binds to multiple DNA binding complexes whose abundances in different neuroblastoma cell lines directly correlate with relative TrkA promoter activity (Chang, 1998). Further dissection of this region using in vitro DNA binding and functional analyses is now underway, with the ultimate goal to identify the transcription factors responsible for variable TrkA expression in neuroblastoma cells.  Figure 2. Consensus binding sites for known transcription factors within the proximal promoter region of the human TrkA gene. We also plan to characterize TrkA promoter regulation within peripheral and central neurons using transgenic mice. Since TrkA expression in sympathetic neurons is associated with terminal differentiation, its regulation should provide important insight into transcriptional mechanisms controlling this critical phase of neuronal development. In addition, recent studies have indicated that TrkA expression is decreased in cholinergic forebrain neurons of patients with Alzheimer's disease. Due to the important role of TrkA signalling in the normal functioning of these neurons, this has led to the suggestion that maintenance of TrkA expression in Alzheimer's patients could slow the progression of this neurodegenerative disease. Thus, understanding what determines TrkA expression and its possible upregulation in these neurons could lead to novel pharmacological treatments.
Office: S4-139
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Neurogenesis consists of a complex series of developmental events that are determined in great part by the actions of specific transcription factors. A critical juncture in the development of neurons is the onset of terminal differentiation, which coincides with, and is intimately linked to, cell cycle exit of dividing neuroblasts. Little is known about the transcriptional mechanisms operating at this interface between growth arrest and terminal neuronal differentiation. Such mechanisms are likely to be important not only for the onset of terminal differentiation, but also for maintenance of its irreversibility or uni-directional nature. Thus, our interest is in understanding the transcription factors and mechanisms that link growth arrest to terminal differentiation and, in particular, those involved in maintenance of the differentiated state of neurons. This question is relevant not only to neuronal development, but to tumorigenesis within the nervous system as well.
55 Lake Avenue North Worcester, MA 01655