Mig12, a novel Opitz syndrome gene product partner,is expressed in the embryonic ventral midline and co-operates with Mid1 to bundle and stabilize microtubules

Background

Opitz G/BBB syndrome is a genetic disorder characterized by developmental midline abnormalities, such as hypertelorism, cleft palate, and hypospadias. The gene responsible for the X-linked form of this disease, MID1, encodes a TRIM/RBCC protein that is anchored to the microtubules. The association of Mid1 with the cytoskeleton is regulated by dynamic phosphorylation, through the interaction with the α4 subunit of phosphatase 2A (PP2A). Mid1 acts as an E3 ubiquitin ligase, regulating PP2A degradation on microtubules.

Results

In spite of these findings, the biological role exerted by the Opitz syndrome gene product is still unclear and the presence of other potential interacting moieties in the Mid1 structure prompted us to search for additional cellular partners. Through a yeast two-hybrid screening approach, we identified a novel gene, MIG12, whose protein product interacts with Mid1. We confirmed by immunoprecipitation that this interaction occurs in vivo and that it is mediated by the Mid1 coiled-coil domain. We found that Mig12 is mainly expressed in the neuroepithelial midline, urogenital apparatus, and digits during embryonic development. Transiently expressed Mig12 is found diffusely in both nucleus and cytoplasm, although it is enriched in the microtubule-organizing center region. Consistently with this, endogenous Mig12 protein is partially detected in the polymerized tubulin fraction after microtubule stabilization. When co-transfected with Mid1, Mig12 is massively recruited to thick filamentous structures composed of tubulin. These microtubule bundles are resistant to high doses of depolymerizing agents and are composed of acetylated tubulin, thus representing stabilized microtubule arrays.

Conclusions

Our findings suggest that Mig12 co-operates with Mid1 to stabilize microtubules. Mid1-Mig12 complexes might be implicated in cellular processes that require microtubule stabilization, such as cell division and migration. Impairment in Mig12/Mid1-mediated microtubule dynamic regulation, during the development of embryonic midline, may cause the pathological signs observed in Opitz syndrome patients.

     

Lessons from models of SOD1-linked familial ALS

Ten years ago, the linkage between mutations in the gene coding for the antioxidant enzyme Cu,Zn superoxide dismutase (SOD1) and the neurodegenerative disease known as familial amyotrophic lateral sclerosis (FALS) was established. This finding has prompted a myriad of new studies in experimental models aimed at investigating the toxic function of the mutant enzymes. The cellular functions that are impaired in motoneurons as a consequence of molecular alterations induced by the expression of FALS SOD1 converge on pathways that might be activated in sporadic ALS by other toxic factors. Recent data demonstrate that, although motoneurons are lost in patients, other cell types are also affected and actively contribute to the pathogenesis of the disease.     

Glutamylated and glycylated tubulin isoforms in the aberrant sperm axoneme of the gall-midge fly, Asphondylia ruebsaameni

The axonemal organization expressed in the sperm flagella of the cecidomyiid dipteran Asphondylia ruebsaameni is unconventional, being characterized by the presence of an exceedingly high number of microtubular doublets and by the absence of both the inner dynein arms and the central pair/radial spoke complex. Consequently, its motility, both in vivo and in vitro, is also peculiar. Using monoclonal antibodies directed against posttranslational modifications, we have analyzed the presence and distribution of glutamylated and glycylated tubulin isoforms in this aberrant axonemal structure, and compared them with those of a reference insect species (Apis mellifera), endowed with a conventional axoneme. Our results have shown that the unorthodox structure and motility of the Asphondylia axoneme are concomitant with: (1). a very low glutamylation extent in the alpha-tubulin subunit, (2). a high level of glutamylation in the beta-subunit, (3). an extremely low total extent of glycylation, with regard to both monoglycylated and polyglycylated sites, either in alpha- or in beta-tubulin, (4). the presence of a strong labeling of glutamylated tubulin isoforms at the proximal end of the axoneme, and (5). a uniform distribution of glutamylated as well as glycylated isoforms along the rest of the axoneme. Thus, our data indicate that tubulin molecular heterogeneity is much lower in the Asphondylia axoneme than in the conventional 9+2 axoneme with regard to both isoform content and isoform distribution along the axoneme.     

Immunohistochemical evaluation of urokinase plasminogen activator receptor in noninvasive and early invasive urothelial papillary neoplasia

OBJECTIVE: To investigate urokinase plasminogen activator receptor (uPAR) expression in urothelial papilloma and in noninvasive and early invasive papillary carcinoma. STUDY DESIGN: The study included 40 cases of papillary neoplasia of the urinary bladder subdivided into 10 cases of urothelial papilloma (UP); 10 of papillary carcinoma, grade 1; 10, grade 2 (G2); and 10, grade 3 (G3). Invasion of the subepithelial connective tissue was present in 5 cases of G2 and 7 cases of G3. According to the 2002 revision of the TNM system, these cases were defined as T1 and the others as Ta. uPAR expression was evaluated with an immunohistochemical technique in 5-microns-thick tissue sections. RESULTS: Difference in the distribution of positive cases in the 4 groups were statistically significant and greatest in G3. Statistically significant differences were also observed between Ta and T1 cases in terms of uPAR intensity. CONCLUSION: Detection of immunoreactivity for uPAR was associated with high grade UP carcinomas. These data indicate that uPAR is potentially an important prognostic factor in bladder carcinoma.     

Glial activation and TNFR-I upregulation precedes motor dysfunction in the spinal cord of mnd mice

Mice homozygous for the spontaneous motor neuron degeneration mutation (mnd) show at the age of 8 months a marked impairment of the motor function and accumulation of lipofuscin granules in the cytoplasm of almost all neurons of the central nervous system.We previously reported a significant increase in GFAP protein levels in the lumbar spinal cord homogenates by western blot analysis and upregulation of TNF, a proinflammatory cytokine, in the motor neurons of lumbar spinal cord of mnd mice, already in a presymptomatic stage (4 months of age). In the present study, using immunohistochemical analysis, we performed a time course in mnd mice (1, 4 and 9 months of age) evaluating the expression and the distribution of astroglial and microglial cells and the expression of both TNF receptors, TNFR-I and TNFR-II. We observed a marked increase in astroglial and microglial cells and in TNFR-I immunoreactivity already at the 4th month. Since motor neuron dysfunction occurs in mnd mice in the absence of evident loss of spinal motor neurons, the present results indicate that the activation of microglial cells and astrocytes is independent from neuronal degeneration. The role of TNF and TNFR-I on motor neurons is still to be demonstrated.     

Endothelial dysfunctions: common denominators in vascular disease

The past 20 years have witnessed enormous progress in our understanding of the biology of vascular endothelium and its role in cardiovascular disease. Stemming from the seminal observations of Furchgott, the concept of a continuous regulation of vascular tone by normal endothelium and alterations of such control in disease states has become one of the most enlightening concepts of cardiovascular research. This review covers a few updates on the topic, illustrating selective areas of recent progress in our understanding of endothelial function in the control of leucocyte adhesion, atherogenesis and vascular tone, as well as the alterations that cause and accompany vascular disease.     

An IQGAP-related gene is activated during tentacle formation in the simple metazoan Hydra

Differentiation of body column epithelial cells into tentacle epithelial cells in Hydra is accompanied by changes in both cell shape and cell-cell contact. The molecular mechanism by which epithelial cells acquire tentacle cell characteristics is unknown. Here we report that expression of a Hydra homologue of the mammalian IQGAP1 protein is strongly upregulated during tentacle formation. Like mammalian IQGAP, Hydra IQGAP1 contains an N-terminal calponin-homology domain, IQ repeats and a conserved C terminus. In adult polyps a high level of Hydra IQGAP1 mRNA is detected at the basis of tentacles. Consistent with a role in tentacle formation, IQGAP1 expression is activated during head regeneration and budding at a time when tentacles are emerging. The observations support the previous hypothesis that IQGAP proteins are involved in cytoskeletal as well as cell-cell contact rearrangements. Received: 25 January 2000 / Accepted: 2 May 2000     

Acute tau knockdown in the hippocampus of adult mice causes learning and memory deficits

Misfolded and hyperphosphorylated tau accumulates in several neurodegenerative disorders including Alzheimer's disease, frontotemporal dementia with Parkinsonism, corticobasal degeneration, progressive supranuclear palsy, Down syndrome, and Pick's disease. Tau is a microtubule‐binding protein, and its role in microtubule stabilization is well defined. In contrast, while growing evidence suggests that tau is also involved in synaptic physiology, a complete assessment of tau function in the adult brain has been hampered by robust developmental compensation of other microtubule‐binding proteins in tau knockout mice. To circumvent these developmental compensations and assess the role of tau in the adult brain, we generated an adeno‐associated virus (AAV) expressing a doxycycline‐inducible short‐hairpin (Sh) RNA targeted to tau, herein referred to as AAV‐ShRNATau. We performed bilateral stereotaxic injections in 7‐month‐old C57Bl6/SJL wild‐type mice with either the AAV‐ShRNATau or a control AAV. We found that acute knockdown of tau in the adult hippocampus significantly impaired motor coordination and spatial memory. Blocking the expression of the AAV‐ShRNATau, thereby allowing tau levels to return to control levels, restored motor coordination and spatial memory. Mechanistically, the reduced tau levels were associated with lower BDNF levels, reduced levels of synaptic proteins associated with learning, and decreased spine density. We provide compelling evidence that tau is necessary for motor and cognitive function in the adult brain, thereby firmly supporting that tau loss‐of‐function may contribute to the clinical manifestations of many tauopathies. These findings have profound clinical implications given that anti‐tau therapies are in clinical trials for Alzheimer's disease.     

Drought stress increased survival and development of emerald ash borer larvae on coevolved Manchurian ash and implicates phloem‐based traits in resistance

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