Plasticity-related Gene 5 Promotes Spine Formation in Murine Hippocampal Neurons

The transmembrane protein plasticity-related genes 3 and 5 (PRG3 and PRG5) increase filopodial formation in various cell lines, independently of Cdc42. However, information on the effects of PRG5 during neuronal development is sparse. Here, we present several lines of evidence for the involvement of PRG5 in the genesis and stabilization of dendritic spines. First, PRG5 was strongly expressed during mouse brain development from embryonic day 14 (E14), peaked around the time of birth, and remained stable at least until early adult stages (i.e. P30). Second, on a subcellular level, PRG5 expression shifted from an equal distribution along all neurites toward accumulation only along dendrites during hippocampal development in vitro. Third, overexpression of PRG5 in immature hippocampal neurons induced formation of spine-like structures ahead of time. Proper amino acid sequences in the extracellular domains (D1 to D3) of PRG5 were a prerequisite for trafficking and induction of spine-like structures, as shown by mutation analysis. Fourth, at stages when spines are present, knockdown of PRG5 reduced the number but not the length of protrusions. This was accompanied by a decrease in the number of excitatory synapses and, consequently, by a reduction of miniature excitatory postsynaptic current frequencies, although miniature excitatory postsynaptic current amplitudes remained similar. In turn, overexpressing PRG5 in mature neurons not only increased Homer-positive spine numbers but also augmented spine head diameters. Mechanistically, PRG5 interacts with phosphorylated phosphatidylinositols, phospholipids involved in dendritic spine formation by different lipid-protein assays. Taken together, our data propose that PRG5 promotes spine formation.     

Scaffold Protein X11α Interacts with Kalirin-7 in Dendrites and Recruits It to Golgi Outposts

Pyramidal neurons in the mammalian forebrain receive their synaptic inputs through their dendritic trees, and dendritic spines are the sites of most excitatory synapses. Dendritic spine structure is important for brain development and plasticity. Kalirin-7 is a guanine nucleotide-exchange factor for the small GTPase Rac1 and is a critical regulator of dendritic spine remodeling. The subcellular localization of kalirin-7 is thought to be important for regulating its function in neurons. A yeast two-hybrid screen has identified the adaptor protein X11α as an interacting partner of kalirin-7. Here, we show that kalirin-7 and X11α form a complex in the brain, and this interaction is mediated by the C terminus of kalirin-7. Kalirin-7 and X11α co-localize at excitatory synapses in cultured cortical neurons. Using time-lapse imaging of fluorescence recovery after photobleaching, we show that X11α is present in a mobile fraction of the postsynaptic density. X11α also localizes to Golgi outposts in dendrites, and its overexpression induces the removal of kalirin-7 from spines and accumulation of kalirin-7 in Golgi outposts. In addition, neurons overexpressing X11α displayed thinner spines. These data support a novel mechanism of regulation of kalirin-7 localization and function in dendrites, providing insight into signaling pathways underlying neuronal plasticity. Dissecting the molecular mechanisms of synaptic structural plasticity will improve our understanding of neuropsychiatric and neurodegenerative disorders, as kalirin-7 has been associated with schizophrenia and Alzheimer disease.     

Coordinated Nuclear and Synaptic Shuttling of Afadin Promotes Spine Plasticity and Histone Modifications

The ability of a neuron to transduce extracellular signals into long lasting changes in neuronal morphology is central to its normal function. Increasing evidence shows that coordinated regulation of synaptic and nuclear signaling in response to NMDA receptor activation is crucial for long term memory, synaptic tagging, and epigenetic signaling. Although mechanisms have been proposed for synapse-to-nuclear communication, it is unclear how signaling is coordinated at both subcompartments. Here, we show that activation of NMDA receptors induces the bi-directional and concomitant shuttling of the scaffold protein afadin from the cytosol to the nucleus and synapses. Activity-dependent afadin nuclear translocation peaked 2 h post-stimulation, was independent of protein synthesis, and occurred concurrently with dendritic spine remodeling. Moreover, activity-dependent afadin nuclear translocation coincides with phosphorylation of histone H3 at serine 10 (H3S10p), a marker of epigenetic modification. Critically, blocking afadin nuclear accumulation attenuated activity-dependent dendritic spine remodeling and H3 phosphorylation. Collectively, these data support a novel model of neuronal nuclear signaling whereby dual-residency proteins undergo activity-dependent bi-directional shuttling from the cytosol to synapses and the nucleus, coordinately regulating dendritic spine remodeling and histone modifications.     

Sarcomere length organization as a design for cooperative function amongst all lumbar spine muscles

The functional design of spine muscles in part dictates their role in moving, loading, and stabilizing the lumbar spine. There have been numerous studies that have examined the isolated properties of these individual muscles. Understanding how these muscles interact and work together, necessary for the prediction of muscle function, spine loading, and stability, is lacking. The objective of this study was to measure sarcomere lengths of lumbar muscles in a neutral cadaveric position and predict the sarcomere operating ranges of these muscles throughout full ranges of spine movements. Sarcomere lengths of seven lumbar muscles in each of seven cadaveric donors were measured using laser diffraction. Using published anatomical coordinate data, superior muscle attachment sites were rotated about each intervertebral joint and the total change in muscle length was used to predict sarcomere length operating ranges. The extensor muscles had short sarcomere lengths in a neutral spine posture and there were no statistically significant differences between extensor muscles. The quadratus lumborum was the only muscle with sarcomere lengths that were optimal for force production in a neutral spine position, and the psoas muscles had the longest lengths in this position. During modeled flexion the extensor, quadratus lumborum, and intertransversarii muscles lengthened so that all muscles operated in the approximate same location on the descending limb of the force-length relationship. The intrinsic properties of lumbar muscles are designed to complement each other. The extensor muscles are all designed to produce maximum force in a mid-flexed posture, and all muscles are designed to operate at similar locations of the force-length relationship at full spine flexion.     

The effect of unstable loading versus unstable support conditions on spine rotational stiffness and spine stability during repetitive lifting

Lumbar spine stability has been extensively researched due to its necessity to facilitate load-bearing human movements and prevent structural injury. The nature of certain human movement tasks are such that they are not equivalent in levels of task-stability (i.e. the stability of the external environment). The goal of the current study was to compare the effects of dynamic lift instability, administered through both the load and base of support, on the dynamic stability (maximal Lyapunov exponents) and stiffness (EMG-driven model) of the lumbar spine during repeated sagittal lifts. Fifteen healthy males performed 23 repetitive lifts with varying conditions of instability at the loading and support interfaces. An increase in spine rotational stiffness occurred during unstable support scenarios resulting in an observed increase in mean and maximum Euclidean norm spine rotational stiffness (p=0.0011). Significant stiffening effects were observed in unstable support conditions about all lumbar spine axes with the exception of lateral bend. Relative to a stable control lifting trial, the addition of both an unstable load as well as an unstable support did not result in a significant change in the local dynamic stability of the lumbar spine (p=0.5592). The results suggest that local dynamic stability of the lumbar spine represents a conserved measure actively controlled, at least in part, by trunk muscle stiffening effects. It is evident therefore that local dynamic stability of the lumbar spine can be modulated effectively within a young-healthy population; however this may not be the case in a patient population.     

Should a standing or seated reference posture be used when normalizing seated spine kinematics?

Currently in the literature there is no consensus on which procedure for normalizing seated spine kinematics is most effective. The objective of this study was to examine the changes in the range of motion (ROM) of seated posture trials when expressed as a percent of maximum standing and seated ROM. A secondary purpose was to determine whether the typical maximum planar calibration movements (flexion, lateral-bend, and axial twist) elicited the respective maximum ROM values for each spine region versus postures with specific movement instruction. Thirteen male participants completed seven different movement trials. These consisted of the maximum planar movement trials, with the remaining four postures being combinations of specific lumbar and thoracic movements. Global and relative angles for the upper-thoracic, mid-thoracic, lower-thoracic, and lumbar regions were calculated and normalized to both a seated and standing reference posture. When normalizing both global and relative angles the standing reference appears optimal for flexion, twisting and lateral bend angles in all spine regions, with the exception of relative flexion angle in the mid-thoracic region. The maximum planar movement trials captured the greatest ROM for each global angle, relative lower-thoracic angle and relative lumbar flexion angle, but did not for all other relative angles in the upper-thoracic, mid-thoracic, and lumbar regions. If future researchers can only collect one reference posture these results recommend that a standing reference posture be collected for normalizing seated spine kinematics, although a seated reference posture should be collected if examining relative flexion angles at the mid-thoracic region.     

Corrective sitting strategies: An examination of muscle activity and spine loading

The purpose of this study was to quantify the load on the lumbar spine of subjects when they are asked to adjust from a slouched sitting posture into an upright posture with one of three different strategies: “free” (no instruction) and two coached patterns: “lumbopelvic” dominant and “thoracic” dominant. The activity of selected muscles and kinematic data was recorded from 20 volunteers while performing the three movement patterns to adjust sitting posture. Moments and forces at the lumbar spine were computed from an anatomically detailed model that uses kinematics and muscle activation as input variables.The lumbopelvic pattern produces less joint moment on the lumbar spine (on average 31.2 ± 3.9 N m) when compared to the thoracic pattern (43.8 ± 5.8 N m). However, the joint compression force was similar for these two patterns, but it was smaller in the free pattern, when no coaching was given (lumbopelvic: 1279 ± 112 N, thoracic: 1367 ± (125 N, free: 1181 ± 118 N). Lower thoracic erector muscle activity and higher lumbar erector activity were measured in the lumbopelvic pattern in comparison with the other two. In summary the lumbopelvic pattern strategy using predominantly the movement of anterior pelvic tilt results in smaller joint moments on the lumbar spine and also positions the lumbar spine closest to the neutral posture minimizing passive tissue stress. This may be the strategy of choice for people with low back flexion intolerance.     

An overview of the role of cancer stem cells in spine tumors with a special focus on chordoma

Primary malignant tumors of the spine are relatively rare, less than 5% of all spinal column tumors. However, these lesions are often among the most difficult to treat and encompass challenging pathologies such as chordoma and a variety of invasive sarcomas. The mechanisms of tumor recurrence after surgical intervention, as well as resistance to radiation and chemotherapy, remain a pervasive and costly problem. Recent evidence has emerged supporting the hypothesis that solid tumors contain a sub-population of cancer cells that possess characteristics normally associated with stem cells. Particularly, the potential for long-term proliferation appears to be restricted to subpopulations of cancer stem cells(CSCs) functionally defined by their capacity to self-renew and give rise to differentiated cells that phenotypically recapitulate the original tumor, thereby causing relapse and patient death. These cancer stem cells present a unique opportunity to better understand the biology of solid tumors in general, as well as targets for future therapeutics. The general objective of the current study is to discuss the fundamental concepts for understanding the role of CSCs with respect to chemoresistance, radioresistance, special cell surface markers, cancer recurrence and metastasis intumors of the osseous spine. This discussion is followed by a specific review of what is known about the role of CSCs in chordoma, the most common primary malignant osseous tumor of the spine.     

Polymorphism in stem females and successive parthenogenetic generations in Brachionus calyciflorus Pallas

We have described the polymorphism in the hatchlings of resting eggs and the morphological variations between the stem females hatched from resting eggs and their successive parthenogenetic generations in the rotifer Brachionus calyciflorus. We hatched resting eggs of B. calyciflorus in two different culture mediums: unconditioned medium (IOM) and Asplanchna-conditioned (ACM). The hatching rate of resting eggs in IOM and ACM were 32.5% and 28.5%, respectively, and showed no significant difference. Stem females hatching from these resting eggs had three morphotypes (unspined, single short-spined, and two short-spined) and over 80% of these females were spineless ones. Moreover, the frequency of each morphotype stem females showed similar tendency in IOM and ACM. The production of a variety of morphotypes among stem mothers—rather than all unspined as has been previously reported for this species—may be regarded as a form of bet-hedging in this population of B. calyciflorus. Phenotypic changes in morphology between the stem females hatched from resting eggs and their successive parthenogenetic generations in B. calyciflorus were found. The possible mechanisms, responsible for high proportion of spineless phenotype at early generations from resting eggs and increased spined phenotype in successive parthenogenetic generations, were discussed in the article.