it is not clear how the loss of TDP-43 results in cell dysfunction or cell loss. TDP-43 was first identified as a protein that binds to DNA, and it is now considered to regulate RNA metabolism. Using a method that identifies the mRNA binding to a specific protein, Hydroxychloroquine in vitro many RNAs that might be regulated by TDP-43 have been identified.[18, 19] These studies have shown that TDP-43 binds to long mRNA molecules with large introns and regulates the splicing and amounts of mRNA in several ways.[18, 19] Consequently, the depletion of TDP-43 might alter pre-mRNA metabolism. Indeed, the alteration of RNA profiles has been reported from cultured cells and model animals with depleted TDP-43. In ALS, alterations of mRNA expression profiles have been reported,[20-22] although the association between TDP-43 and these alterations of mRNA observed in ALS remain to be clarified. To our knowledge, POLDIP3 is the only gene in which the splicing is directly regulated by TDP-43 and is altered in spinal motor
neurons with ALS but not in brain with frontotemporal lobar degeneration.[23, 24] In addition, immunohisotochemical analysis indicated that several genes selleck inhibitor processed by TDP-43 express key molecules for function or survival of spinal motor neurons and show decreasing amounts of products. However, it is unclear how the function of TDP-43 correlates with the depletion of these products. Thus, the specific functions of TDP-43 have not been fully evaluated in vitro or in ALS patients. These disturbances of RNA metabolism might not be explained simply by the
loss of TDP-43 function on pre-mRNA. Therefore, some researchers have speculated that TDP-43 serves another function associated with RNA metabolism. TDP-43 forms foci in the nucleus and associates with several nuclear bodies, suggesting that TDP-43 plays a role in Cediranib (AZD2171) the functioning of nuclear bodies. Nuclear bodies are classified and identified by their unique protein components. In addition, most of these bodies are tightly associated with a unique RNA and regulate that particular RNA metabolism.[28, 29] In contrast to cytoplasmic organelles, nuclear bodies do not have a membranous structure that separates their contents from nucleoplasm. Thus, the components of nuclear bodies are frequently exchanged between the bodies and the nucleoplasm. The dynamism of the components is a unique characteristic of nuclear bodies. The protein components decrease their mobility in nuclear bodies as compared to that in nucleoplasm. Thus, the bodies are recognized based on the increased concentration of the component protein. The nucleolus and Cajal bodies are the most well-known nuclear bodies. The nucleolus is the center for maturation of rRNA, whereas Cajal bodies are sites for the maturation of U snRNAs and consist of coilin.