TAR DNA-binding protein (TDP-43) is an evolutionarily conserved heterogeneous nuclear ribonucleoprotein (hnRNP) involved in RNA processing, whose abnormal cellular distribution and post-translational modification are key markers of certain neurodegenerative diseases, such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration. We generated human cell lines expressing tagged forms of wild-type and mutant TDP-43 and observed that TDP-43 controls its own expression through a negative feedback loop. The RNA-binding properties of TDP-43 are essential for the autoregulatory activity through binding to 3 0 UTR sequences in its own mRNA. Our analysis indicated that the C-terminal region of TDP-43, which mediates TDP-43-hnRNP interactions, is also required for self-regulation. TDP-43 binding to its 3 0 UTR does not significantly change the pre-mRNA splicing pattern but promotes RNA instability. Moreover, blocking exosome-mediated degradation partially recovers TDP-43 levels. Our findings demonstrate that cellular TDP-43 levels are under tight control and it is likely that disease-associated TDP-43 aggregates disrupt TDP-43 self-regulation, thus contributing to pathogenesis.

One of the fundamental issues in RNA splicing research is represented by understanding how the spliceosome can successfully define exons and introns in a huge variety of pre-mRNA molecules with nucleotide-precision. Since its first description, researchers in this field have identified and characterized many fundamental elements and players capable of affecting the splicing process, both in a negative and positive manner. Indeed, it can be argued that today we know a great deal about the forces that make an exon, an exon and an intron, an intron. As will be discussed in this review, these decisions are a result of a complex combinatorial control resulting from many different factors/influences. Most importantly, these influences act across several levels of complexity starting from the relatively simple interaction between two consensus 5' and 3' splice sites to much more complex factors: such as the interplay between silencer or enhancer sequences, transcriptional processivity, genomic milieu, nucleosome positioning, and histone modifications at the chromatin level. Depending on local contexts, all these factors will act either antagonistically or synergistically to decide the exon/intron fate of any given RNA sequence. At present, however, what we still lack is a precise understanding of how all these processes add up to help the spliceosome reach a decision. Therefore, it is expected that future challenges in splicing research will be the careful characterization of all these influences to improve our ability to predict splicing choices in different organisms or in specific contexts.

TDP‐43 has recently been described as the major component of the inclusions found in the brain of patients with a variety of neurodegenerative diseases, such as frontotemporal lobar degeneration and amyotrophic lateral sclerosis. TDP‐43 is a ubiquitous protein whose specific functions are probably crucial to establishing its pathogenic role. Apart from its involvement in transcription, splicing and mRNA stability, TDP‐43 has also been described as a Drosha‐associated protein. However, our knowledge of the role of TDP‐43 in the microRNA (miRNA) synthesis pathway is limited to the association mentioned above. Here we report for the first time which changes occur in the total miRNA population following TDP‐43 knockdown in culture cells. In particular, we have observed that let‐7b and miR‐663 expression levels are down‐ and upregulated, respectively. Interestingly, both miRNAs are capable of binding directly to TDP‐43 in different positions: within the miRNA sequence itself (let‐7b) or in the hairpin precursor (miR‐663). Using microarray data and real‐time PCR we have also identified several candidate transcripts whose expression levels are selectively affected by these TDP‐43–miRNA interactions.

Background: TDP-43 is the principal protein component of cellular inclusion in ALS and FTLD. Results: Tandem repetitions of TDP-43 residues 331-369 induce cellular aggregates that recruit endogenous TDP-43. Conclusion: Our results establish a cell-based TDP-43 aggregation model. Significance: This model will be useful to investigate TDP-43 aggregation and develop strategies/effectors able to prevent/ reduce this phenomenon.

In recent times, high-throughput screening analyses have broadly defined the RNA cellular targets of TDP-43, a nuclear factor involved in neurodegeneration. A common outcome of all these studies is that changing the expression levels of this protein can alter the expression of several hundred RNAs within cells. What still remains to be clarified is which changes represent direct cellular targets of TDP-43 or just secondary variations due to the general role played by this protein in RNA metabolism. Using an HTS-based splicing junction analysis we identified at least six bona fide splicing events that are consistent with being controlled by TDP-43. Validation of the data, both in neuronal and non-neuronal cell lines demonstrated that TDP-43 substantially alters the levels of isoform expression in four genes potentially important for neuropathology: MADD/IG20, STAG2, FNIP1 and BRD8. For MADD/IG20 and STAG2, these changes could also be confirmed at the protein level. These alterations were also observed in a cellular model that successfully mimics TDP-43 loss of function effects following its aggregation. Most importantly, our study demonstrates that cell cycle alterations induced by TDP-43 knockdown can be recovered by restoring the STAG2, an important component of the cohesin complex, normal splicing profile.