To prevent neurodegeneration: HDAC6 uses different strategies for different challenges
Neurodegenerative diseases are characterized by progressive dysfunction and death of neurons in specific areas of the nervous system. Loss of neurons is often associated with multiple stresses such as abnormal aggregation of misfolded proteins, deficiency of protein degradation system, mitochondrial dysfunction and excessive oxidative products. HDAC6 has recently been suggested to be an integral factor that copes with these stresses. In this mini-review, we summarize our current understanding of how HDAC6 promotes inclusion formation, facilitates autophagic degradation of protein aggregates and dysfunctional mitochondria. Finally, the possibility for HDAC6 to be a potential preventional and therapeutical target of some neurodegenerative diseases is put forward.
Information between neurons and the target cells they innervated passes through sites of functional contact called synapses. How synapses form and are altered by sensory or cognitive experience is central to understand nervous system function. Studies of synapse formation and plasticity have concentrated on a few "model" synapses. The vertebrate neuromuscular junction (NMJ), the synapse between a motoneuron in the spinal cord and a skeletal muscle fiber, is one such model synapse. The extracellular matrix proteoglycan agrin plays an essential organizing role at the NMJ. Agrin is also present at some synapses in the brain and in other organs in the periphery, but its function outside the NMJ is unclear. The core signaling pathway for agrin at the NMJ, which is still incompletely defined, includes molecules specifically involved in this cascade and molecules used in other signaling pathways in many cells. Mitogen-activated protein kinases (MAPKs) are evolutionarily conserved components of intracellular signaling modules that control a myriad of cellular processes. This article reviews emerging evidence that suggests that MAPKs are involved in agrin signaling at the NMJ and in the putative functions of agrin in the formation of a subset of synapses in the brain.
The Nucleolinus: A disappearing, forgotten, and (maybe) misnamed organelle
It is common knowledge that many of the cell components we study today were discovered more than a century ago. Some have been renamed due to a newer understanding of their physiology or composition, and in some cases the old terminology is abandoned. It is unusual, however, to find a structure that has not been renamed but simply forgotten. This appears to be the case for the nucleolinus, discovered at least 150 years ago and studied by Agassiz, Haekel, Montgomery, and others until it virtually dropped from the literature in the early 1970s. The nucleolinus was thought to have a role in cell division, but with little knowledge of its composition and no molecular markers (until recently) available for its study, we do not know if the nucleolinus is a ubiquitous structure or an antiquated descriptor. This brief article relates most of what we know about the nucleolinus and where to find more information. Our growing knowledge concerning the role of the closely allied nucleolus in cell cycle regulation suggests that renewed study of the nucleolinus will yield important information about the biogenesis and evolution of the cell division apparatus.
Evolution of glycosaminoglycans: Comparative biochemical study
Glycosaminoglycans, a major component of the extracellular matrix molecules in animal tissues, play important roles in various physiological events. Glycosaminoglycans are found in not only vertebrates but also many invertebrates, implying a conserved function in the animal kingdom. Here, we discuss the analysis of glycosaminoglycans in 11 invertebrate phyla focusing on structure as well as physiological functions elucidated in model organisms. Various sulfated structures of heparan sulfate are widely distributed from very primitive organisms to humans, indicating an involvement in fundamental biological processes. By contrast, chondroitin/dermatan sulfate from lower organisms is limited in its structural complexity and often associated with a particular function. The presence of hyaluronic acid outside of vertebrates has been reported only in a mollusk.
Indispensable roles of mammalian Cbl family proteins as negative regulators of protein tyrosine kinase signaling: Insights from in vivo models
All higher eukaryotes utilize protein tyrosine kinases (PTKs) as switches to control a variety of cellular signals. Intriguingly, many PTKs have been identified as proto-oncogenes whose aberrant expression, mutations or co-option by pathogens can lead to human malignancies. Thus, it is obvious that PTK functions must be precisely regulated in order to maintain homeostasis of an organism. Investigations over the past fifteen years have revealed that members of the Cbl family proteins can serve as negative regulators of PTK signaling, and biochemical and cell biological studies have unraveled the mechanistic basis of this regulation. Yet, it is only recently that the field begun to appreciate the real significance of this novel regulatory apparatus in shaping PTK-mediated signaling in organismic contexts and in human diseases. Here, we discuss recent progress in murine models that are beginning to provide insights into the critical roles of Cbl proteins in physiological pathways, with important implications in understanding how aberrations of Cbl proteins contribute to oncogenesis.
The society of our “out of Africa” ancestors (I): The migrant warriors that colonized the world
The “out of Africa” hypothesis proposes that a small group of Homo sapiens left Africa 80,000 years ago, spreading the mitochondrial haplotype L3 throughout the Earth.1-10 Little effort has been made to try to reconstruct the society and culture of the tribe that left Africa to populate the rest of the world.1 Here, I find that hunter-gatherers that belong to mitochondrial haplotypes L0, L1 and L2 do not have a culture of ritualized fights. In contrast to this, almost all L3 derived hunter-gatherers have a more belligerent culture that includes ritualized fights such as wrestling, stick fights or headhunting expeditions. This appears to be independent of their environment because ritualized fights occur in all climates, from the tropics to the arctic. There is also a correlation between mitochondrial haplotypes and warfare propensity or the use of murder and suicide to resolve conflicts. The data implicate that the original human population outside Africa is descended from only two closely related sub-branches that practiced ritual fighting and had a higher propensity towards warfare and the use of murder for conflict resolution. This warfare culture may have given the out of Africa migrants a competitive advantage to colonize the world. But it could also have crucially influenced the subsequent history of The Earth. In the future, it would be interesting to see how we could further reconstruct the society and culture of the “Out of Africa Tribe.”
The expression of SPARC in human tumors is consistent with its role during cell competition
In Drosophila, the elimination of viable but suboptimal cells is mediated by cell competition, ensuring that these cells do not accumulate during development. In addition, certain genes such as the Drosophila homologue of human c-myc (dmyc) are able to transform cells into supercompetitors, which eliminate neighboring wild-type cells by apoptosis and overproliferate leaving total cell numbers unchanged. We have recently identified Drosophila SPARC as an early marker transcriptionally upregulated in loser cells that provides a transient protection by inhibiting caspase activation in outcompeted cells. Here, we explore whether the expression of SPARC in human tumors is consistent with a role for cell competition during human cancer and find that, consistent with the existence of competitive interactions between cancer and normal cells, SPARC is upregulated at the tumor-host boundaries in several types of human cancer.
Studies of novel interactions between Nck and VAV SH3 domains
Following T-cell antigen receptor (TCR) engagement, a multi-molecular complex consisting of SLP-76, Nck, and VAV1 is formed and recruited to the T-cell antigen-presenting-cell (APC) interaction site. This complex is crucial for the regulation of the actin machinery. The molecules Nck (an adaptor) and VAV1 (a GEF for small G-proteins) were previously shown to bind SLP-76. Using high-resolution imaging techniques, together with gene silencing and biochemical analysis, we studied the dynamics of this signaling complex formation. We recently showed that VAV1 and Nck can bind each other independently of SLP-76. This direct interaction is mediated by the binding of the Nck C-terminal SH3 domain and the VAV1 N-terminal SH3 domain. This interaction contributes to the cooperative nature of the complex formation. This observation was confirmed in functional studies: disruption of the Nck-VAV1 interaction strongly inhibited actin polymerization. Here, we show that Nck-VAV1 interaction is not required for Ca2+ mobilization, since a point mutation in the VAV1 N-terminal SH3 domain, which prevent the direct interaction between Nck and VAV1, has no effect on Ca2+ flux and minimal effects on ZAP-70, LAT, or PLCγ1 phosphorylation.
Yeast dynamin implicated in endocytic scission and the disassembly of endocytic components
The yeast dynamin-related GTPase Vps1 has been implicated in a range of cellular functions including vacuolar protein sorting, protein trafficking, organization of peroxisome, and endocytosis.1-2 Vps1 is present at endocytic sites and may be directly involved in endocytic vesicle invagination through its membrane-tubulating activity. Here, evidence supporting the functional link between Vps1 and the yeast amphiphysin Rvs167 in vesicle invagination is discussed. Though the disassembly of endocytic factors from pinched-off endocytic vesicles appears to be tightly regulated in a spatiotemporal manner, we are far from having complete understanding of the underlying mechanism. In this study, we provide evidence that Vps1 plays a role in the uncoating of endocytic proteins from post-internalized vesicles, based on the observation of a quick disassembly of two endocytic coat proteins Ent1 and Ent2 in cells lacking Vps1.
How does a protein with dual mitotic spindle and extracellular matrix receptor functions affect tumor susceptibility and progression?
The mechanisms responsible for the oncogenic effects of the hyaluronan (HA) receptor and mitotic spindle binding protein, RHAMM, are poorly understood. On one hand, extracellular RHAMM interacts with HA and cell-surface receptors such as CD44 to coordinately activate the MAPK/ERK1,2 pathway, thus contributing to the spread and proliferation of tumor cells. On the other hand, intracellular RHAMM decorates mitotic spindles and is necessary for spindle formation and progression through G2/M and overexpression or loss of RHAMM can result in multi-pole spindles and chromosome mis-segregation. The deregulation of these intracellular functions could lead to genomic instability and fuel tumor progression. This suggests that both extracellular and intracellular RHAMM can promote tumor progression. Intracellular RHAMM can bind directly to ERK1 to form complexes with ERK2, MEK1 and ERK1,2 substrates, and we present a model whereby RHAMM’s function is as a scaffold protein, controlling activation and targeting of ERK1,2 to specific substrates.
Calcium signaling components in the human pathogen Cryptococcus neoformans
Calcium signaling through calmodulin and the phosphatase calcineurin are required for key events of the biology of the human pathogen Cryptococcus neoformans, including mating, morphogenesis, growth at 37°C and virulence. In a recent work we described the functional characterization of a new component of this calcium signaling network: the vacuolar calcium exchanger Vcx1. This transporter is involved in calcium tolerance and virulence in C. neoformans. Two other uncharacterized calcium transporters which are putative orthologs of Saccharomyces cerevisiae PMC1 (a vacuolar calcium ATPase) and PMR1 (a Golgi calcium ATPase) are also functional in C. neoformans. No ortholog of CRZ1, the target of calcineurin in other fungi, has been identified in C. neoformans, indicating a high complexity in cryptococcal calcium-related pathways. Future studies are necessary for the complete understanding of calcium signaling regulation in C. neoformans.
Lifestyle and compact genome of the body louse provide a unique functional genomics opportunity
Barry R. Pittendrigh, May R. Berenbaum, Manfredo J. Seufferheld, Venu M. Margam, Joseph P. Strycharz, Yoon Kyong S., Weilin Sun, Robert Reenan, Si Hyeock Lee and John M. Clark
Pages 188 - 191 http://dx.doi.org/10.4161/cib.4.2.14279
Lifestyle and compact genome of the body louse provide a unique functional genomics opportunity
The body louse, with its recently sequenced genome, is now primed to serve as a powerful model organism for addressing fundamental questions relating to how insects interact with their environment. One characteristic of the body louse that facilitates this research is the size of its genome—the smallest insect genome sequenced to date. This diminutive genome must nonetheless control an organism that senses and responds to its environment, reacting to threats of corporal and genomic integrity. Additionally, the body louse transmits several important human diseases compared to its very close relative, the head louse, which does not. Therefore, these two organisms comprise an excellent model system for studying molecular mechanisms associated with vector competence. To understand more fully the development of vector/pathogen interactions, we have developed an in vitro bioassay system and determined that the body louse genome appears to contain the genes necessary for RNAi. The body louse will therefore be useful for determining the set of conditions permissive to the evolution of vector competence.
Nature and nurture: A step towards investigating their interactions in the wild
The debate about the relative importance of nature versus nurture has been around for decades, but despite this, there has been very little evidence about how these might in fact interact to drive evolution in the wild. Recently, the identification of a comparable methodology for analyzing both genetic and social effects of phenotypic variation, revealed that fitness variation in a free-living population of dolphin was driven by a strong social and genetic interaction. This study not only provides evidence that nature and nurture do interact to drive phenotypic evolution but also represents a step towards partitioning the effects of genetic, social, environmental factors, and their multiway interactions to better understand phenotypic evolution in the wild.
Legionella pneumophila infection is enhanced in a RacH-null mutant of Dictyostelium
Recently we reported that Dictyostelium cells ingest Legionella pneumophila by macropinocytosis, whereas other bacteria, such as Escherichia coli, Mycobacterium avium, Neisseria meningitidis or Salmonella typhimurium, are taken up by phagocytosis.1 In contrast to phagocytosis, macropinocytosis is partially inhibited by PI3K or PTEN inactivation, whereas both processes are sensitive to PLC inhibition. Independently from reduced uptake, L. pneumophila proliferates more efficiently in PI3K-null than in wild type cells. PI3K inactivation also neutralizes resistance to infection conferred by constitutively expressing the endo-lysosomal iron transporter Nramp1. We have shown this to be due to altered recruitment of the V-H+ ATPase, but not Nramp1, in the Legionella-containing vacuole (LCV) early during infection.1 As further evidence for impaired LCV acidification we examine here the effects of disrupting the small G protein RacH on Legionella infection.
Cells in multicellular organisms are under constant mechanical stress, and often the plasma membrane (PM) is compromised. Fortunately, there is a vigorous repair mechanism that rapidly (within seconds) reseals the wound site by fusion with an internal membrane patch. Downstream events, remodeling of the injury site, and forming replacement PM, must be carried out quickly (within minutes) if a cell is to survive multiple sequential injuries. The repertoire of proteins required to repair breaks (the PM repairome) is one of the major unknowns in this area of research. As an initial approach to defining the PM repairome, a cell surface biotinylation protocol was developed to identify intracellular proteins that become exposed at the site of reversible PM injury. It is likely that at least some of these proteins are important mediators of repair. These initial studies led to a surprising finding, namely the identification of some nuclear and endoplasmic reticulum resident proteins transiently exposed at the surface of cells that ultimately recovered from PM damage. Thus, in reversible mechanical damage to the PM, underlying cellular structures may also be injured, and will also require mechanisms for repair. Other proteins at wound sites were previously identified docking partners for pathogenic bacteria and viruses (vimentin and nucleolin), or found to be upregulated and exposed on the surface of cancer cells (nucleolin and nucleophosmin-1). The new information from these studies may lead to development of novel antimicrobial and antineoplastic drugs.
The hematopoietic stem cell polarization and migration: A dynamic link between RhoA signaling pathway, microtubule network and ganglioside-based membrane microdomains
The polarization and migration of eukaryotic cells are fundamental processes for the development and maintenance of a tissue. These aspects gain especial interest when it comes to stem and progenitor cells in the way that their manipulation might open new avenues in regenerative therapy. In recent years, novel biological facets of migrating hematopoietic stem cells were revealed by several groups including ours. Among these features, the polarization of their membranous (proteins and lipids) and cytoplasmic constituents, which leads to the formation of a specialized sub-cellular structure located at the rear pole – the uropod – has gained increasing interest. In a new study we have demonstrated that such phenomena involve a coordinated mechanism between Rho GTPase signaling and the microtubule network. Specifically, our results based on the use of synthetic inhibitors and RNA interference suggest that the activity of RhoA and its effector ROCK I is indispensable for cell polarization and the active reorganization of microtubules that are required for migration.
The filamentous (F)-actin regulatory protein cortactin plays an important role in tumor cell movement and invasion by promoting and stabilizing actin related protein (Arp)2/3-mediated actin networks necessary for plasma membrane protrusion. Cortactin is a substrate for ERK1/2 and Src family kinases, with previous in vitro findings demonstrating ERK1/2 phosphorylation of cortactin as a positive and Src phosphorylation as a negative regulatory event in promoting Arp2/3 activation through neuronal Wiskott Aldrich Syndrome protein (N-WASp). Evidence for this regulatory cortactin “switch” in cells has been hampered due to the lack of phosphorylation-specific antibodies that recognize ERK1/2-phosphorylated cortactin. Our findings with phosphorylation-specific antibodies against these ERK1/2 sites (pS405 and pS418) indicate that cortactin can be co-phosphorylated at 405/418 and tyrosine residues targeted by Src family tyrosine kinases. These results indicate that the ERK/Src cortactin switch is not the sole mechanism by which ERK1/2 and tyrosine phosphorylation events regulate cortactin function in cell systems.
Linking LIMK1 deficiency to hyperacusis and progressive hearing loss in individuals with Williams syndrome
Abstract Williams syndrome (a.k.a. Williams-Beuren Syndrome) is a multisystem disorder caused by the hemizygous deletion of a 1.6-Mb region at 7q11.23 encompassing about 26 genes, including that encoding LIM kinase 1 (LIMK1). Individuals with Williams Syndrome manifest hyperacusis and progressive hearing loss, and hyperacusis early onset suggests that it could be associated with one of the deleted genes. Based on our results about the critical role of LIM kinases in the regulation of the motile response of cochlear outer hair cells and cochlear amplification, we propose here that a reduced expression of LIMK1 in outer hair cells would be the major underlying cause of the hyperacusis and progressive hearing loss observed in patients with Williams Syndrome. Moreover, we propose a novel model of gain-control for cochlear amplification based on the LIMK-mediated regulation of slow motility of cochlear outer hair cells.
Readdressing synaptic pruning theory for schizophrenia: Combination of brain imaging and cell biology
Disturbance in the synapse has been suggested in the pathology of schizophrenia, especially through examination of autopsied brains from patients with the disease. Nonetheless, it has been unclear whether and how such disturbance is associated with the onset and progression of the disease in young adulthood. Some studies with magnetic resonance spectroscopy (MRS) have suggested that overpruning of dendritic spines may occur in the prodromal and early stages of schizophrenia. In addition, our recent study indicates that DISC1, a promising risk factor for schizophrenia, has a crucial role in the maintenance of the dendritic spine in association with activation of the NMDA-type glutamate receptor1. Disturbance of spine maintenance can be linked to aberrant synaptic pruning during postnatal brain maturation. Biological studies with genetic models may provide us with an opportunity to validate experimentally the synaptic pruning theory for schizophrenia. An integrative strategy of brain imaging and cell biology may be a promising approach to address a key biological question for mental illnesses.
On the water lapping of felines and the water running of lizards: A unifying physical perspective
We consider two biological phenomena taking place at the air-water interface, the water lapping of felines and the water running of lizards. Although seemingly disparate motions, we show that they are intimately linked by their underlying hydrodynamics and belong to a broader class of processes called Froude mechanisms. We describe how both felines and lizards exploit inertia to defeat gravity, and discuss water lapping and water running in the broader context of water exit and water entry, respectively.
Experience-dependent plasticity in visual cortex: Dendritic spines and visual responsiveness
To determine the relationship between synaptic structural changes and cortical function, we recently published a study where we imaged dendritic spines using two-photon in vivo microscopy while monitoring network activity in the visual cortex using intrinsic signal imaging. By manipulating cortical activity levels by dark-rearing mice and re-exposing them to light, we found a close inverse correspondence between dendritic spine structural dynamics and visually-evoked cortical function on a timescale of days. Light exposure following dark-rearing slowly increased visually evoked cortical processing and stabilized dendritic spine structure, an effect partially mimicked by diazepam injections in dark reared mice suggesting that this slow recovery is mediated by inhibitory signaling. Surprisingly, very brief (2 hour) periods of light exposure led to an NMDA-dependent rapid re-organization of cortical networks with an early emergence of visually-evoked cortical activation and enhanced spine dynamics. Here we further explore the relationship between spine morphology and visual function.
Remodeling of brain circuits, including the formation, modification, and elimination of synaptic structures, occurs throughout life as animals adapt to their environment. Until very recently, known mechanisms for experience-dependent synaptic plasticity had placed neurons and their structural interactions with astrocytes in the spotlight. However microglia, the immune cells of the brain, are very active even in the absence of pathological insults and their processes periodically contact dendritic spines and axon terminals in vivo.1-3 This intriguing behavior prompted us to explore, using electron microscopy and two-photon in vivo imaging in the primary visual cortex of juvenile mice, a possible role for quiescent microglia in the modification of synaptic structures.4 Our work uncovered subtle changes in the behavior of microglia during manipulations of visual experience including regulation of perisynaptic extracellular spaces, contact with subsets of structurally dynamic and transient dendritic spines, and phagocytic engulfment of intact synapses. Based on these results, here we further discuss three means of synapse modification or elimination that could be mediated by microglia in the context of normal experience-dependent plasticity.
Astrocytes have been recently identified as important components of the tripartite synaptic complex. There is growing evidence that astrocytes regulate synaptic functions, in part, through the release of gliotransmitters. In a recent study, we have demonstrated that ephrinB3 could stimulate astrocytic release of D-serine through activation of EphB3 and EphA4 receptors. Eph receptors regulate this response by inducing the dephosphorylation of PKCa and activation of serine racemase to convert L-serine to D-serine. We now investigated whether ephrinB3 would increase the release of glutamine, which is also synthesized from serine and play important roles in regulating synaptic responses. Using HPLC, we observed an enhanced release of L/D-serine and glutamine from cultured astrocytes following ephrinB1 and/or ephrinB3 stimulation. In the absence of EphB3 and EphA4, ephrinB3-enhanced release of L/D-serine and glutamine was not observed. These studies provide evidence that Eph receptors may play broader roles in regulating gliotransmitter release from astrocytes, which could have important implications on synaptic transmission and learning and memory processes.
Working memory for Braille is shaped by experience
Tactile working memory was found to be more developed in completely blind (congenital and acquired) than in semi-sighted subjects, indicating that experience plays a crucial role in shaping working memory. A model of working memory, adapted from the classical model proposed by Baddeley and Hitch (1) and Baddeley (2), is presented where the connection strengths of a highly cross-modal network are altered through experience.
Systems biomechanics of centrosome positioning: A conserved complexity
Positioning of centrosomes within cells determines the directionality of cell division, as well as directionality of cellular activities in the interphase. This brief review focuses on similarities (and differences) of centrosome positioning during early divisions in the Caenorhabditis embryo and during the interaction of T lymphocytes with other cells in the course of immune response. In the study of the two phenomena, a synergy of experimentation and numerical mechanical analysis has recently been achieved. The picture that emerges from these studies is one in which simple physical forces under the constraints of the basic cell structure lead to complex, "life-like" mechanical behavior. This behavior includes instability of equilibria, irreversibility of structural transitions, and multidimensional, multiperiodic oscillations. This new picture of cell mechanics may form an interesting paradigm for future research.
Recent evidence indicates that the evolution of ultrasonic hearing in echolocating bats and cetaceans has involved adaptive amino acid replacements in the cochlear gene prestin. A substantial number of these changes have occurred in parallel in both groups, suggesting that particular amino acid residues might confer greater auditory sensitivity to high frequencies. Here we review some of these findings, and consider whether similar signatures of prestin protein sequence evolution also occur in mammals that possess high frequency hearing for passive localization, and, conversely, whether this gene has undergone less change in mammals that lack high frequency hearing.
Vacuolar trafficking and Candida albicans pathogenesis
The vacuole is likely to play a variety of roles in supporting host colonization and infection by pathogenic species of fungi. In the human pathogen Candida albicans, the vacuole undergoes dynamic morphological shifts during the production of the tissue invasive hyphal form, and this organelle is required for virulence. Recent efforts in my lab have focused on defining which vacuolar trafficking pathways are required for C. albicans hyphal growth and pathogenesis. Our results indicate that there are several distinct trafficking routes between the Golgi apparatus and vacuole. However, there is a large degree of functional overlap between each with respect to their roles in hyphal growth and virulence. Herein we consider these results and propose that during hyphal growth, specific trafficking routes maybe less important than the aggregate vacuolar trafficking capacity.
Dissecting protein interactions during cytokinesis
Appropriate assembly and constriction of the acto-myosin based contractile ring is essential for the final separation of the two daughter cells in mitosis. This is orchestrated by the small GTPase Rho as well as convergent signals from the prior events of mitosis. Contractile ring assembly requires the physical interaction of structural proteins like the microtubules of the central spindle, motor proteins and Rho activators. These and the interaction of newly localized proteins downstream of active Rho are essential for stability of the contractile ring and its proper constriction. Here, we discuss our recent findings that reveal a complex network of protein interactions during the early stages of cytokinesis. This includes evidence for a direct interaction between Polo Kinase and RacGAP50C as well as unpublished data suggesting other interactions of interest within the contractile ring.