Deficiency in parvalbumin, but not in calbindin D-28k upregulates mitochondrial volume and decreases smooth endoplasmic reticulum surface selectively in a peripheral, subplasmalemmal region in the soma of Purkinje cells

The Ca(2+)-binding proteins parvalbumin (PV) and calbindin D-28k (CB) are key players in the intracellular Ca(2+)-buffering in specific cells including neurons and have profound effects on spatiotemporal aspects of Ca(2+) transients. The previously observed increase in mitochondrial volume density in fast-twitch muscle of PV-/- mice is viewed as a specific compensation mechanism to maintain Ca(2+) homeostasis. Since cerebellar Purkinje cells (PC) are characterized by high expression levels of the Ca(2+) buffers PV and CB, the question was raised, whether homeostatic mechanisms are induced in PC lacking these buffers. Mitochondrial volume density, i.e. relative mitochondrial mass was increased by 40% in the soma of PV-/- PC. Upregulation of mitochondrial volume density was not homogenous throughout the soma, but was selectively restricted to a peripheral region of 1.5 microm width underneath the plasma membrane. Accompanied was a decreased surface of subplasmalemmal smooth endoplasmic reticulum (sPL-sER) in a shell of 0.5 microm thickness underneath the plasma membrane. These alterations were specific for the absence of the "slow-onset" buffer PV, since in CB-/- mice neither changes in peripheral mitochondria nor in sPL-sER were observed. This implicates that the morphological alterations are aimed to specifically substitute the function of the slow buffer PV. We propose a novel concept that homeostatic mechanisms of components involved in Ca(2+) homeostasis do not always occur at the level of similar or closely related molecules. Rather the cell attempts to restore spatiotemporal aspects of Ca(2+) signals prevailing in the undisturbed (wildtype) situation by subtly fine tuning existing components involved in the regulation of Ca(2+) fluxes.

Transcriptional dysregulation during myeloid transformation in AML

The current paradigm on leukemogenesis indicates that leukemias are propagated by leukemic stem cells. The genomic events and pathways involved in the transformation of hematopoietic precursors into leukemic stem cells are increasingly understood. This concept is based on genomic mutations or functional dysregulation of transcription factors in malignant cells of patients with acute myeloid leukemia (AML). Loss of the CCAAT/enhancer binding protein-alpha (CEBPA) function in myeloid cells in vitro and in vivo leads to a differentiation block, similar to that observed in blasts from AML patients. CEBPA alterations in specific subgroups of AML comprise genomic mutations leading to dominant-negative mutant proteins, transcriptional suppression by leukemic fusion proteins, translational inhibition by activated RNA-binding proteins, and functional inhibition by phosphorylation or increased proteasomal-dependent degradation. The PU.1 gene can be mutated or its expression or function can be blocked by leukemogenic fusion proteins in AML. Point mutations in the RUNX1/AML1 gene are also observed in specific subtypes of AML, in addition to RUNX1 being the most frequent target for chromosomal translocation in AML. These data are persuasive evidence that impaired function of particular transcription factors contributes directly to the development of human AML, and restoring their function represents a promising target for novel therapeutic strategies in AML.

Insulin-like growth factor type-1 receptor down-regulation associated with dwarfism in Holstein calves

Perturbations in endocrine functions can impact normal growth. Endocrine traits were studied in three dwarf calves exhibiting retarded but proportionate growth and four phenotypically normal half-siblings, sired by the same bull, and four unrelated control calves. Plasma 3,5,3'-triiodothyronine and thyroxine concentrations in dwarfs and half-siblings were in the physiological range and responded normally to injected thyroid-releasing hormone. Plasma glucagon concentrations were different (dwarfs, controls>half-siblings; P<0.05). Plasma growth hormone (GH), insulin-like growth factor-1 (IGF-1) and insulin concentrations in the three groups during an 8-h period were similar, but integrated GH concentrations (areas under concentration curves) were different (dwarfs>controls, P<0.02; half-siblings>controls, P=0.08). Responses of GH to xylazine and to a GH-releasing-factor analogue were similar in dwarfs and half-siblings. Relative gene expression of IGF-1, IGF-2, GH receptor (GHR), insulin receptor, IGF-1 type-1 and -2 receptors (IGF-1R, IGF-2R), and IGF binding proteins were measured in liver and anconeus muscle. GHR mRNA levels were different in liver (dwarfs

Airway remodelling in children with cystic fibrosis

BACKGROUND: The relationship between airway structural changes and inflammation is unclear in early cystic fibrosis (CF) lung disease. A study was undertaken to determine changes in airway remodelling in children with CF compared with appropriate disease and healthy controls. METHODS: Bronchoalveolar lavage and endobronchial biopsy were performed in a cross-sectional study of 43 children with CF (aged 0.3-16.8 years), 7 children with primary ciliary dyskinesia (PCD), 26 with chronic respiratory symptoms (CRS) investigated for recurrent infection and/or cough and 7 control children with no lower airway symptoms. Inflammatory cells, cytokines, proteases and matrix constituents were measured in bronchoalveolar lavage fluid (BALF). Reticular basement membrane (RBM) thickness was measured on biopsy specimens using light microscopy. RESULTS: Increased concentrations of elastin, glycosaminoglycans and collagen were found in BALF from children with CF compared with the CRS group and controls, each correlating positively with age, neutrophil count and proteases (elastase activity and matrix metalloproteinase-9 (MMP-9) concentration). There were significant negative correlations between certain of these and pulmonary function (forced expiratory volume in 1 s) in the CF group (elastin: r = -0.45, p<0.05; MMP-9:TIMP-1 ratio: r = -0.47, p<0.05). Median RBM thickness was greater in the CF group than in the controls (5.9 microm vs 4.0 microm, p<0.01) and correlated positively with levels of transforming growth factor-beta(1) (TGF-beta(1); r = 0.53, p = 0.01), although not with other inflammatory markers or pulmonary function. CONCLUSIONS: This study provides evidence for two forms of airway remodelling in children with CF: (1) matrix breakdown, related to inflammation, proteolysis and impaired pulmonary function, and (2) RBM thickening, related to TGF-beta(1) concentration but independent of other markers of inflammation.

The etiology of liver damage imparts cytokines transforming growth factor beta1 or interleukin-13 as driving forces in fibrogenesis

It is unknown whether transforming growth factor beta1 (TGF-beta1) signaling uniformly participates in fibrogenic chronic liver diseases, irrespective of the underlying origin, or if other cytokines such as interleukin (IL)-13 share in fibrogenesis (e.g., due to regulatory effects on type I pro-collagen expression). TGF-beta1 signaling events were scored in 396 liver tissue samples from patients with diverse chronic liver diseases, including hepatitis B virus (HBV), hepatitis C virus (HCV), Schistosoma japonicum infection, and steatosis/steatohepatitis. Phospho-Smad2 staining correlated significantly with fibrotic stage in patients with HBV infection (n = 112, P < 0.001) and steatosis/steatohepatitis (n = 120, P < 0.01), but not in patients with HCV infection (n = 77, P > 0.05). In tissue with HBx protein expression, phospho-Smad2 was detectable, suggesting a functional link between viral protein expression and TGF-beta1 signaling. For IL-13, immunostaining correlated with fibrotic stage in patients with HCV infection and steatosis/steatohepatitis. IL-13 protein was more abundant in liver tissue lysates from three HCV patients compared with controls, as were IL-13 serum levels in 68 patients with chronic HCV infection compared with 20 healthy volunteers (72.87 +/- 26.38 versus 45.41 +/- 3.73, P < 0.001). Immunohistochemistry results suggest that IL-13-mediated liver fibrogenesis may take place in the absence of phospho-signal transducer and activator of transcription protein 6 signaling. In a subgroup of patients with advanced liver fibrosis (stage > or =3), neither TGF-beta nor IL-13 signaling was detectable. Conclusion: Depending on the cause of liver damage, a predominance of TGF-beta or IL-13 signaling is found. TGF-beta1 predominance is detected in HBV-related liver fibrogenesis and IL-13 predominance in chronic HCV infection. In some instances, the underlying fibrogenic mediator remains enigmatic.

Chronic rejection in lung allografts: immunohistological analysis of fibrogenesis

In ongoing chronic rejection after lung transplantation, alveolar interstitial fibrosis develops. However, little is known about the mechanisms involved. In order to investigate these mechanisms, expression of extracellular matrix molecules (ECM) (undulin, decorin, tenascin, laminin, and fibronectin) and cytokines [transforming growth factor (TGF)-beta 1, TGF-beta 3, platelet-derived growth factor (PDGF), and PDGF receptor] were semiquantitatively evaluated in chronically rejected lung allografts, using standard immunohistochemical techniques. Additionally, the presence of macrophages was analysed. The present study demonstrates an increased infiltration of macrophages with a concomitant upregulation of cytokines (TGF-beta 1, TGF-beta 3, and PDGF) and an increased deposition of ECM in chronic lung rejection. These cytokines have an important role in the stimulation of fibroblasts which are a major source of ECM. Upregulated expression of ECM in the alveolar interstitial space leads to alveolar malfunction by thickening of the wall and, thus, is one of the causative factors of respiratory dysfunction in chronic lung graft rejection.

Plasma membrane-associated annexin A6 reduces Ca2+ entry by stabilizing the cortical actin cytoskeleton

The annexins are a family of Ca(2+)- and phospholipid-binding proteins, which interact with membranes upon increase of [Ca(2+)](i) or during cytoplasmic acidification. The transient nature of the membrane binding of annexins complicates the study of their influence on intracellular processes. To address the function of annexins at the plasma membrane (PM), we fused fluorescent protein-tagged annexins A6, A1, and A2 with H- and K-Ras membrane anchors. Stable PM localization of membrane-anchored annexin A6 significantly decreased the store-operated Ca(2+) entry (SOCE), but did not influence the rates of Ca(2+) extrusion. This attenuation was specific for annexin A6 because PM-anchored annexins A1 and A2 did not alter SOCE. Membrane association of annexin A6 was necessary for a measurable decrease of SOCE, because cytoplasmic annexin A6 had no effect on Ca(2+) entry as long as [Ca(2+)](i) was below the threshold of annexin A6-membrane translocation. However, when [Ca(2+)](i) reached the levels necessary for the Ca(2+)-dependent PM association of ectopically expressed wild-type annexin A6, SOCE was also inhibited. Conversely, knockdown of the endogenous annexin A6 in HEK293 cells resulted in an elevated Ca(2+) entry. Constitutive PM localization of annexin A6 caused a rearrangement and accumulation of F-actin at the PM, indicating a stabilized cortical cytoskeleton. Consistent with these findings, disruption of the actin cytoskeleton using latrunculin A abolished the inhibitory effect of PM-anchored annexin A6 on SOCE. In agreement with the inhibitory effect of annexin A6 on SOCE, constitutive PM localization of annexin A6 inhibited cell proliferation. Taken together, our results implicate annexin A6 in the actin-dependent regulation of Ca(2+) entry, with consequences for the rates of cell proliferation.

Immune response deviation and enhanced expression of chemokine receptor CCR4 in TBI patients due to unknown serum factors

BACKGROUND: Severe brain trauma leads to an activation of the immune system. To this date, neither the exact perturbation of the specific immune reaction induced by the traumatic brain injury (TBI), nor the interactions leading to the infiltration of peripheral immune cells into the brain are fully understood. PATIENTS AND METHODS: Serum was collected from 17 patients with TBI and a long bone fracture, 24 patients with an isolated long bone fracture and from healthy individuals. The effect of the serum on normal human monocytes and T-lymphocytes was tested in vitro by assessing proliferation and expression of surface markers, chemokine receptors and cytokines. RESULTS: Serum collected from patients with a TBI and a long bone fracture increased the expression of the chemokine receptor CCR4 in monocytes when compared to patients with an isolated long bone fracture. Extending this comparison to T-lymphocytes, the serum from TBI patients induced lower proliferation rates and decreased expression of the pro-inflammatory cytokine TNF-alpha, while simultaneously increasing the secretion of immune-modulatory cytokines (IL-4, IL-10 and TGF-beta) (p<0.05). CONCLUSION: Patients with a TBI release currently unknown soluble factors into the circulating blood that up regulate expression of chemokine receptor CCR4 in peripheral blood monocytes whilst concurrently inducing expression of immunosuppressive cytokines by activated T-lymphocytes.

BMP-2 induces the expression of chondrocyte-specific genes in bovine synovium-derived progenitor cells cultured in three-dimensional alginate hydrogel

OBJECTIVE: According to recent reports, the synovial membrane may contain mesenchymal stem cells with the potential to differentiate into chondrocytes under appropriate conditions. In order to assess the usefulness of synovium-derived progenitor cells for the purposes of cartilage tissue engineering, we explored their requirements for the expression of chondrocyte-specific genes after expansion in vitro. DESIGN: Mesenchymal progenitor cells were isolated from the synovial membranes of bovine shoulder joints and expanded in two-dimensions on plastic surfaces. They were then seeded either as micromass cultures or as single cells within alginate gels, which were cultured in serum-free medium. Under these three-dimensional conditions, chondrogenesis is known to be supported and maintained. Cell cultures were exposed either to bone morphogenetic protein-2 (BMP-2) or to isoforms of transforming growth factor-beta (TGF-beta). The levels of mRNA for Sox9, collagen types I and II and aggrecan were determined by RT-PCR. RESULTS: When transferred to alginate gel cultures, the fibroblast-like synovial cells assumed a rounded form. BMP-2, but not isoforms of TGF-beta, stimulated, in a dose-dependent manner, the production of messenger RNAs (mRNAs) for Sox9, type II collagen and aggrecan. Under optimal conditions, the expression levels of cartilage-specific genes were comparable to those within cultured articular cartilage chondrocytes. However, in contrast to cultured articular cartilage chondrocytes, synovial cells exposed to BMP-2 continued to express the mRNA for alpha1(I) collagen. CONCLUSIONS: This study demonstrates that bovine synovium-derived mesenchymal progenitor cells can be induced to express chondrocyte-specific genes. However, the differentiation process is not complete under the chosen conditions. The stimulation conditions required for full transformation must now be delineated.

Comparison of mesencephalic free-floating tissue culture grafts and cell suspension grafts in the 6-hydroxydopamine-lesioned rat

Ventral mesencephalon (VM) of fetal rat and human origin grown as free-floating roller-tube (FFRT) cultures can survive subsequent grafting to the adult rat striatum. To further explore the functional efficacy of such grafts, embryonic day 13 ventral mesencephalic tissue was grafted either after 7 days in culture or directly as dissociated cell suspensions, and compared with regard to neuronal survival and ability to normalize rotational behavior in adult rats with unilateral 6-hydroxydopamine (6-OHDA) lesions. Other lesioned rats received injections of cell-free medium and served as controls. The amphetamine-induced rotational behavior of all 6-OHDA-lesioned animals was monitored at various time points from 18 days before transplantation and up to 80 days after transplantation. Tyrosine hydroxylase (TH) immunostaining of the histologically processed brains served to assess the long-term survival of grafted dopaminergic neurons and to correlate that with the behavioral effects. Additional cultures and acutely prepared explants were also fixed and stored for histological investigation in order to estimate the loss of dopaminergic neurons in culture and after transplantation. Similar behavioral improvements in terms of significant reductions in amphetamine-induced rotations were observed in rats grafted with FFRT cultures (127%) and rats grafted with cell suspensions (122%), while control animals showed no normalization of rotational behavior. At 84 days after transplantation, there were similar numbers of TH-immunoreactive (TH-ir) neurons in grafts of cultured tissue (775 +/- 98, mean +/- SEM) and grafts of fresh, dissociated cell suspension (806 +/- 105, mean +/- SEM). Cell counts in fresh explants, 7-day-old cultures, and grafted cultures revealed a 68.2% loss of TH-ir cells 7 days after explantation, with an additional 23.1% loss after grafting, leaving 8.7% of the original number of TH-ir cells in the intracerebral grafts. This is to be compared with a survival rate of 9.1% for the TH-ir cells in the cell-suspension grafts. Immunostaining for the calcium-binding proteins calretinin, calbindin, and parvalbumin showed no differences in the neuronal expression of these proteins between the two graft types. In conclusion, we found comparable dopaminergic cell survival and functional effects of tissue-culture grafts and cell-suspension grafts, which currently is the type of graft most commonly used for experimental and clinical grafting. In this sense the result is promising for the development of an effective in vitro storage of fetal nigral tissue, which at the same time would allow neuroprotective and neurotrophic treatment prior to intracerebral transplantation.

Different adaptation of IGF-I and its IGFBPs in dairy cows during a negative energy balance in early lactation and a negative energy balance induced by feed restriction in mid-lactation

Control of metabolic pathways is a major task of the somatotropic axis and its constituents. Insulinlike growth-factor binding proteins (IGFBPs) bind IGF-I and -II and act as carriers and regulators of their activities in blood, body fluids and tissues. Over two periods of physiological adaptation, this study investigated the binding pattern of IGF-I to IGFBPs in the plasma of 50 multiparous Holstein dairy cows and identified relationships with the hepatic mRNA abundance of IGFBPs and plasma IGF-I during the lactational negative energy balance (NEB) and during a deliberately induced NEB by feed restriction. Period 1 lasted from week 3 antepartum (a.p.) to week 12 postpartum (p.p.) and period 2, the period of feed restriction, started at around 100 DIM and lasted for three weeks with a control (C) and a restricted group (R). Blood samples and liver biopsies were collected in week 3 a.p., and in weeks 1 and 4 p.p. of period 1 and in weeks 0 and 3 of period 2. For column chromatography of IGFBPs, plasma samples of all animals were pooled by group and time points of sampling. Plasma IGF-I dropped from week 3 a.p. to week 1 p.p. and thereafter increased until week 0 (period 2) and did not change up to week 3 of period 2. The binding of IGF-I to plasma IGFBP-1 and -2 increased in period 1 from week 3 a.p. to week 4 p.p., while at the same time it decreased for IGFBP-3. During period 2, the binding of IGF-I to plasma IGFBP-1 and -2 decreased for both groups, but less for R cows. In C cows, the IGF-I binding to IGFBP-3 in plasma increased from week 0 to week 3 of period 2, whereas R cows showed a slight decrease. In period 1, hepatic mRNA abundance of IGFBP-3 followed the plasma IGFBP-3 binding in contrast to the mRNA abundances of IGFBP-1 and -2. The latter increased from week 3 a.p. to week 1 p.p. and decreased afterwards whereas IGF-I binding to IGFBP-1 and -2 increased. In week 3 of period 2, the binding of IGF-I to IGFBP-1 and -2 and their hepatic mRNA abundance were higher in R cows compared to C cows. Hepatic mRNA abundance of IGF-I was consistently positively correlated with plasma IGF-I, especially pronounced during the NEBs in week 1 p.p. (period 1) and in week 3 (period 2) in R cows. While no distinct relation between mRNA abundance of IGFBP-1 and plasma IGF-I was evident, the mRNA abundance of IGFBP-2 was inversely related to plasma IGF-I over all experimental time points independent of treatment. The mRNA abundance of IGFBP-3 was particularly correlated with plasma IGF-I during the 2 experimental stages of a NEB. Obviously IGFBP-3, but not IGFBP-1 and -2, binding in plasma closely followed the respective pattern of hepatic mRNA abundance during the entire experimental period. The fact that changes in the different plasma IGFBPs during altering metabolic stages in different stages of lactation do not always strictly follow their mRNA abundance in liver suggests tissues other than the liver flexibly contributing to the IGFBP pool in plasma as well as a partially post-transcriptional regulation of IGFBP synthesis.

Expression of trefoil factor 1 in the developing and adult rat ventral mesencephalon

Trefoil factor 1 (TFF1) belongs to a family of secreted peptides with a characteristic tree-looped trefoil structure. TFFs are mainly expressed in the gastrointestinal tract where they play a critical role in the function of the mucosal barrier. TFF1 has been suggested as a neuropeptide, but not much is known about its expression and function in the central nervous system. We investigated the expression of TFF1 in the developing and adult rat midbrain. In the adult ventral mesencephalon, TFF1-immunoreactive (-ir) cells were predominantly found in the substantia nigra pars compacta (SNc), the ventral tegmental area (VTA) and in periaqueductal areas. While around 90% of the TFF1-ir cells in the SNc co-expressed tyrosine hydroxylase (TH), only a subpopulation of the TH-ir neurons expressed TFF1. Some TFF1-ir cells in the SNc co-expressed the calcium-binding proteins calbindin or calretinin and nearly all were NeuN-ir confirming a neuronal phenotype, which was supported by lack of co-localization with the astroglial marker glial fibrillary acidic protein (GFAP). Interestingly, at postnatal (P) day 7 and P14, a significantly higher proportion of TH-ir neurons in the SNc co-expressed TFF1 as compared to P21. In contrast, the proportion of TFF1-ir cells expressing TH remained unchanged during postnatal development. Furthermore, significantly more TH-ir neurons expressed TFF1 in the SNc, compared to the VTA at all four time-points investigated. Injection of the tracer fluorogold into the striatum of adult rats resulted in retrograde labeling of several TFF1 expressing cells in the SNc showing that a significant fraction of the TFF1-ir cells were projection neurons. This was also reflected by unilateral loss of TFF1-ir cells in SNc of 6-hydroxylase-lesioned hemiparkinsonian rats. In conclusion, we show for the first time that distinct subpopulations of midbrain dopaminergic neurons express TFF1, and that this expression pattern is altered in a rat model of Parkinson's disease.

The Oxytricha trifallax macronuclear genome: a complex eukaryotic genome with 16,000 tiny chromosomes.

The macronuclear genome of the ciliate Oxytricha trifallax displays an extreme and unique eukaryotic genome architecture with extensive genomic variation. During sexual genome development, the expressed, somatic macronuclear genome is whittled down to the genic portion of a small fraction (∼5%) of its precursor "silent" germline micronuclear genome by a process of "unscrambling" and fragmentation. The tiny macronuclear "nanochromosomes" typically encode single, protein-coding genes (a small portion, 10%, encode 2-8 genes), have minimal noncoding regions, and are differentially amplified to an average of ∼2,000 copies. We report the high-quality genome assembly of ∼16,000 complete nanochromosomes (∼50 Mb haploid genome size) that vary from 469 bp to 66 kb long (mean ∼3.2 kb) and encode ∼18,500 genes. Alternative DNA fragmentation processes ∼10% of the nanochromosomes into multiple isoforms that usually encode complete genes. Nucleotide diversity in the macronucleus is very high (SNP heterozygosity is ∼4.0%), suggesting that Oxytricha trifallax may have one of the largest known effective population sizes of eukaryotes. Comparison to other ciliates with nonscrambled genomes and long macronuclear chromosomes (on the order of 100 kb) suggests several candidate proteins that could be involved in genome rearrangement, including domesticated MULE and IS1595-like DDE transposases. The assembly of the highly fragmented Oxytricha macronuclear genome is the first completed genome with such an unusual architecture. This genome sequence provides tantalizing glimpses into novel molecular biology and evolution. For example, Oxytricha maintains tens of millions of telomeres per cell and has also evolved an intriguing expansion of telomere end-binding proteins. In conjunction with the micronuclear genome in progress, the O. trifallax macronuclear genome will provide an invaluable resource for investigating programmed genome rearrangements, complementing studies of rearrangements arising during evolution and disease.

Characterization of Phosphorylation- and RNA-Dependent UPF1 Interactors by Quantitative Proteomics

Human up-frameshift 1 (UPF1) is an ATP-dependent RNA helicase and phosphoprotein implicated in several biological processes but is best known for its key function in nonsense-mediated mRNA decay (NMD). Here we employed a combination of stable isotope labeling of amino acids in cell culture experiments to determine by quantitative proteomics UPF1 interactors. We used this approach to distinguish between RNA-mediated and protein-mediated UPF1 interactors and to determine proteins that preferentially bind the hypo- or the hyper-phosphorylated form of UPF1. Confirming and expanding previous studies, we identified the eukaryotic initiation factor 3 (eIF3) as a prominent protein-mediated interactor of UPF1. However, unlike previously reported, eIF3 binds to UPF1 independently of UPF1’s phosphorylation state. Furthermore, our data revealed many nucleus-associated RNA-binding proteins that preferentially associate with hyper-phosphorylated UPF1 in an RNase-sensitive manner, suggesting that UPF1 gets recruited to mRNA and becomes phosphorylated before being exported to the cytoplasm as part of the mRNP.

Unravelling the multiple roles of FUS in RNA processing and on ALS pathogenesis

Two genes with related functions in RNA biogenesis were recently reported in patients with familial ALS: the FUS/TLS gene at the ALS6 locus and the TARDBP/TDP-43 gene at the ALS10 locus [1, 2]. FUS has been implicated to function in several steps of gene expression, including transcription regulation [3], RNA splicing [4, 5], mRNA transport in neurons [6] and, interestingly, in microRNA (miRNA) processing [7]. The goal of this project is to identify the molecular mechanisms leading to the development of FUS mutations-associated ALS. Specifically, we want to test the hypothesis that these FUS mutations misregulate miRNA levels that in turn affect the expression of genes critical for motor neuron survival. In addition we want to test whether misregulation of the miRNA profile is a common feature in ALS. We have performed immunoprecipitations from total extracts of 293T cells expressing FLAG-tagged FUS to characterize its interactome by mass spectrometry. This proteomic study not only revealed a strong interaction of FUS with splicing factors, but shows that FUS might be involved in many, quite different pathways. To map which parts of the FUS protein contribute to the interaction with splicing factors, we have performed a set of experiments with a series of missense and deletion mutants. With this approach, we will not only gain information on the binding partners of FUS along with a map of the required domains for the interactions, but it will also help to unravel whether certain ALS-associated FUS mutations lead to a loss or gain of function due to gain or loss of interactors. Additionally, we have performed quantitative interactomics using SILAC to identify interactome differences of ALS-associated FUS mutants. To this end we have performed immunoprecipitations of total extract from 293T cells, stably transduced with constructs expressing wild-type FUS-FLAG as well as three different ALS-associated mutants (G156E, R244C, P525L). First results indicate striking differences in the interactome with certain RNA binding proteins. We are now validating these candidates in order to reveal the importance of these differential interactions in the context of ALS.