A reconstruction of Telephina bicuspis, a pelagic trilobite from the Middle Ordovician of the Oslo Region, Norway

Well preserved parts of Telephina bicuspis described from dark limestone concretions of Llanvirn age, in the Oslo Region, Norway, exhibit many features associated with a pelagic life style for this trilobite. The free cheek has a huge holochroal eye with perfectly square lenses and a long genal spine which is unique in being directed vertically upwards rather than ventrally. Additional spines include an occipital spine, the macro spine on the rachis of the 6th thoracic segment and paired spines from each of the two rachial rings of the pygidium. These spines may have had a hydrodynamic and stabilizing function. The genal spine could have had a sensory function or been a dimorphic feature. The hypostoma is figured for the first time and a reconstruction is given for the complete exoskeleton.     

Structure, ontogeny, and moulting of the olenid trilobite Ctenopyge (Eoctenopyge) angusta Westergård, 1922 from the upper Cambrian of Västergötland, Sweden

The genus Ctenopyge is known mainly from disarticulated sclerites and from rare complete specimens flattened in shales. Hitherto, very few specimens have been found preserved intact and in three dimensions. In a recently discovered fauna, however, in the Peltura minor Subzone in Västergötland, central Sweden, there occur several species of Ctenopyge , of which many are complete and superbly preserved; moreover they occur at all stages of growth. Of these the abundant Ctenopyge ( Eoctenopyge ) angusta Westergård, 1922 is described and reconstructed here as an adult, and the entire ontogeny is documented for all post–protaspid growth stages. Many characters typical of the adult, such as the long genal spines and the caudal spine, develop very early in ontogeny, and the relative dimensions of the cranidium do not greatly change during growth. Macropleural spines, however, develop later. The transitory pygidium, relatively large and shield–shaped in the early meraspid, later becomes very small as the ten thoracic segments are liberated; a median spine develops on the last thoracic segment only at the holaspid stage. Instar groupings can be clearly distinguished for the early stages. Recurrent associations of sclerites are interpreted as moulting configurations. As reconstructed, the genal spines are horizontal and parallel with the extended thorax; an adaptation which presumably allowed the trilobite to rest on the sea floor.     

Morphological observation of antler regeneration in red deer (Cervus elaphus)

Deer antler offers a unique opportunity to explore how nature solves the problem of mammalian appendage regeneration. Annual antler renewal is an example of epimorphic regeneration, which is known to take place through initial blastema formation. Detailed examination of the early process of antler regeneration, however, has thus far been lacking. Therefore, we conducted morphological observations on antler regeneration from naturally cast and artificially created pedicle/antler stumps. On the naturally cast pedicle stumps, early antler regeneration underwent four distinguishable stages (with the Chinese equivalent names): casting of previous hard antlers (oil lamp bowl), early wound healing (tiger eye), late wound healing and early regeneration (millstone), and formation of main beam and brown tine (small saddle). Overall, no cone-shaped regenerate, a common feature to blastema-based regeneration, was observed. Taken together with the examination on the sagittal plane of each regenerating stage sample, we found that there are considerable overlaps between late-stage wound healing and the establishment of posterior and anterior growth centers. Observation of antler regeneration from the artificially created stumps showed that the regeneration potential of antler remnants was significantly reduced compared with that of pedicle tissue. Interestingly, the distal portion of a pedicle stump had greater regeneration potential than the proximal region, although this differential potential may not be constitutive, but rather caused by whether or not pedicle antlerogenic tissue becomes closely associated with the enveloping skin at the cut plane. Antler formation could take place from the distal peripheral tissues of an antler/pedicle stump, without the obvious participation of the entire central bony portion. Overall, our morphological results do not support the notion that antler regeneration takes place through the initial formation of a blastema; rather, it may be a stem cell-based process.     

Post-embryonic development of the Furongian (late Cambrian) trilobite Tsinania canens: implications for life mode and phylogeny

SUMMARY The current concept of the order Asaphida was proposed to accommodate some Cambrian and Ordovician trilobite clades that are characterized by the possession of a ventral median suture. The family Tsinaniidae was recently suggested to be a member of the order Asaphida on the basis of its close morphological similarity to Asaphidae. Postembryonic development of the tsinaniid trilobite, Tsinania canens , from the Furongian (late Cambrian) Hwajeol Formation of Korea, reveals that this trilobite had an adult-like protaspis. Notable morphological changes with growth comprise the effacement of dorsal furrows, sudden degeneration of pygidial spines, regression of genal spines, and loss of a triangular rostral plate to form a ventral median suture. Programmed cell death may be responsible for degenerating the pygidial and genal spines during ontogeny. Morphological changes with growth, such as the loss of pygidial spines, modification of pleural tips, and effacement of dorsal furrows, suggest that T. canens changed its life mode during ontogeny from benthic crawling to infaunal. The protaspid morphology and the immature morphology of T. canens retaining genal and pygidial spines suggest that tsinaniids bear a close affinity to leiostegioids of the order Corynexochida. Accordingly, development of a ventral median suture in T. canens demonstrates that the ventral median suture could have evolved polyphyletically, and thus the current concept of the order Asaphida needs to be revised.     

Structure, development, and plasticity of dendritic spines.

Dendritic spines are distinguished by their shapes, subcellular composition, and synaptic receptor subtypes. Recent studies show that actin-dependent movements take place in spine heads, that spines emerge from stubby and shaft synapses after dendritic filopodia disappear, and that spines can form without synaptic activation, are maintained by optimal activation, and are lost with excessive activation or during degeneration.     

Spine skeleton morphogenesis during regeneration in clypeasteroid and camarodont sea urchins

The process of skeleton morphogenesis is described for broken and totally removed spines in clypeasteroid (hollow spine) and camarodont (solid spine) sea urchins. Spine regeneration after total spine removal is completed in 40–45 days in clypeasteroids and in 60–70 days in camarodont sea urchins. Along with common stages of formation of longitudinal ribs in both hollow and solid spines, fundamental differences were found between the initial stages of reparative growth of the spine shaft. The spine shaft is formed from a single median process in clypeasteroids and from many simultaneously growing processes in camarodont sea urchins. Reparative morphogenesis of totally removed and partly broken spines in clypeasteroid sea urchins and totally removed spines in camarodont sea urchins leads to the formation of a skeletal structure identical to the intact spine. However, during the regeneration of broken camarodont spines, lateral growth is markedly retarded. As a result, the regenerated part of the spine shaft has a smaller diameter when the initial spine length is achieved. A hypothesis is proposed on a paedomorphic origin of spines in the clypeasteroid sea urchins on the basis of the juvenile stage of definitive spines in the camarodont sea urchins.     

EphA signaling promotes actin-based dendritic spine remodeling through slingshot phosphatase

Actin cytoskeletal remodeling plays a critical role in transforming the morphology of subcellular structures across various cell types. In the brain, restructuring of dendritic spines through actin cytoskeleletal reorganization is implicated in the regulation of synaptic efficacy and the storage of information in neural circuits. However, the upstream pathways that provoke actin-based spine changes remain only partly understood. Here we show that EphA receptor signaling remodels spines by triggering a sequence of events involving actin filament rearrangement and synapse/spine reorganization. Rapid EphA signaling over minutes activates the actin filament depolymerizing/severing factor cofilin, alters F-actin distribution in spines, and causes transient spine elongation through the phosphatases slingshot 1 (SSH1) and calcineurin/protein phosphatase 2B (PP2B). This early phase of spine extension is followed by synaptic reorganization events that take place over minutes to hours and involve the relocation of pre/postsynaptic components and ultimately spine retraction. Thus, EphA receptors utilize discrete cellular and molecular pathways to promote actin-based structural plasticity of excitatory synapses.     

Growth of the calcareous skeleton during regeneration of spines of the sea urchin,strongylocentrotus purpuratus (stimpson): A light and scanning electron microscopic study

Growth of the skeleton of regenerating spines of the sea urchin, Strongylocentrotus purpuratus, was studied with the light and scanning electron microscopes during the formation of a growth ring or cycle. Growth was initiated about three days after fracture and was linear between 5 and about 40 days after fracture, with a mean rate of 0.16 mm/day. There-after, a decline in growth rate was observed, being attributed to abrasion. The new skeleton first appeared as minute, conical ?micro-spines”? on the fractured surface of the spine shaft initiating regeneration of the inner zone of meshwork. Subsequent growth of micro-spines of both the developing inner zone of meshwork, and an outer zone of radiating wedges, formed a conical fenestrated skeleton on the fractured surface of the shaft. Further deposition of micro-spines along the shaft, initially at the level of fracture, formed meshwork which gradually became solidified externally resulting in a new cycle about 60 days after fracture. In contrast, a new cycle was initiated at the milled ring in non-fractured spines during total regeneration on bare tubercles, demonstrating that growth of spines also takes place in the absence of fracture. Experiments conducted in vitro demonstrate that spine regeneration is not a polar phenomenon.     

Systematic regulation of spine sizes and densities in pyramidal neurons

Dendritic spines receive most excitatory inputs in the CNS. Recent evidence has demonstrated that the spine head volume is linearly correlated with the readily releasable pool of neurotransmitter and the PSD size. These correlations can be used to functionally interpret spine morphology. Using Golgi impregnations and light microscopy, we reconstructed 23000 spines from pyramidal neurons in layers 2/3, 4, 5 and 6 of mouse primary visual cortex and CA1 hippocampal region and measured their spine head diameters and densities. Spine head diameters and densities are variable within and across cells, although they are similar between apical and basal dendrites. When compared to other regions, layer 5 neurons have larger spine heads and CA1 neurons higher spine densities. Interestingly, we detect a correlation between spine head diameter and interspine distance within and across cells, whereby larger spines are spaced further away from each other than smaller spines. Finally, in CA1 neurons, spine head diameters are larger, and spine density lower, in distal apical dendrites (>200 microm from soma) compared to proximal regions. These results reveal that spine morphologies and densities, and therefore synaptic properties, are jointly modulated with respect to cortical region, laminar position, and, in some cases, even the position of the spine along the dendritic tree. Individual neurons also appear to regulate their apical and basal spine densities and morphologies in concert. Our data provide evidence for a homeostatic control of excitatory synaptic strength.     

Structure and development of spines over the skin surface of the river puffer Takifugu obscurus (Tetraodontidae,Teleostei) during larval growth

The histological structure and development of spines on the skin surface of Takifugu obscurus were studied during larval development conducted artificially with an average 30‰ salinity and 18.0–20.3°C water temperature. The epidermis comprises an outermost layer, middle layer, and the stratum germinativum, and contains three types of gland cells: small spherical or flask‐shaped mucous cells, larger sacciform mucous cells, and large granular cells. The dermis and subcutis follow. The spines first appear over the ventral region at 10 days after hatching and consist of two parts: a central long tapering portion which projects into the epidermis and eventually outside of the body, and a short supporting basal portion that is embedded within the stratum compactum layer of the dermis. The central, long tapering portion has two very short processes on top until 25 days after hatching, but these two separate spines fuse into one 30 days after hatching. In contrast, the short supporting spines rooted at the base consist of three to six small spines (usually four to five spines) and are present even in the adult stage. Therefore, calcareous spines consisting of one central long spine and three to six smaller supporting spines form tetra‐ and septaradiate spines (mainly penta‐ and hexaradiate). The spines first appear over the ventral region.     

Calcium dynamics of spines depend on their dendritic location

Dendritic spines are morphologically and functionally heterogeneous. To understand this diversity, we use two-photon imaging of layer 5 neocortical pyramidal cells and measure action potential-evoked [Ca(2+)]i transients in spines. Spine calcium kinetics are controlled by (i) the diameter of the parent dendrite, (ii) the length of the spine neck, and (iii) the strength of spine calcium pumps. These factors produce different calcium dynamics in spines from basal, proximal apical, and distal apical dendrites, differences that are more pronounced without exogenous buffers. In proximal and distal apical dendrites, different calcium dynamics correlate with different susceptibility to synaptic depression, and modifying calcium kinetics in spines changes the expression of long-term depression. Thus, the spine location apparently determines its calcium dynamics and synaptic plasticity. Our results highlight the precision in design of neocortical neurons.     

The postnatal development of lamina V pyramidal cells in the sensomotor cortex of the albino rat. 2. Quantitative studies on Golgi preparations]

Using Golgi-Cox preparates the postnatal development (1st to 90th day after birth) of the patterns of apical dendrite spines in layer V pyramids in albino rat sensorimotor cortex is represented. Especially it is reported about the evolution of the total amount of apical dendrite spines, of length of apical dendrites, of spine density (spine dendrite quotients, DQ), of interspinous distance (space between two adjacent visible spines, in the proximal dendrite with increasing spine distribution and in the district with crest of spine distribution separately) and finally of cell body length.     

Tissue Regeneration and Biomineralization in Sea Urchins: Role of Notch Signaling and Presence of Stem Cell Markers

Echinoderms represent a phylum with exceptional regenerative capabilities that can reconstruct both external appendages and internal organs. Mechanistic understanding of the cellular pathways involved in regeneration in these animals has been hampered by the limited genomic tools and limited ability to manipulate regenerative processes. We present a functional assay to investigate mechanisms of tissue regeneration and biomineralization by measuring the regrowth of amputated tube feet (sensory and motor appendages) and spines in the sea urchin, Lytechinus variegatus. The ability to manipulate regeneration was demonstrated by concentration-dependent inhibition of regrowth of spines and tube feet by treatment with the mitotic inhibitor, vincristine. Treatment with the gamma-secretase inhibitor DAPT resulted in a concentration-dependent inhibition of regrowth, indicating that both tube feet and spine regeneration require functional Notch signaling. Stem cell markers (Piwi and Vasa) were expressed in tube feet and spine tissue, and Vasa-positive cells were localized throughout the epidermis of tube feet by immunohistochemistry, suggesting the existence of multipotent progenitor cells in these highly regenerative appendages. The presence of Vasa protein in other somatic tissues (e.g. esophagus, radial nerve, and a sub-population of coelomocytes) suggests that multipotent cells are present throughout adult sea urchins and may contribute to normal homeostasis in addition to regeneration. Mechanistic insight into the cellular pathways governing the tremendous regenerative capacity of echinoderms may reveal processes that can be modulated for regenerative therapies, shed light on the evolution of regeneration, and enable the ability to predict how these processes will respond to changing environmental conditions.     

Regulation after proximal or distal transposition of limb regeneration blastemas and determination of the proximal boundary of the regenerate.

When blastemas of several stages of differentiation were grafted in normal orientation to stump levels proximal or distal to their level of origin, normal limbs regenerated. Histological and autoradiographic studies of the development of these regulated limbs showed that the grafted blastemas formed only structures normally distal to their level of origin. In the case of a blastema transplanted proximally, regulation occurred by intercalary regeneration from the stump, whereas, when blastemas were transplanted distally, regulation appeared to take place within the blastema itself by a distal shift in its pattern of organization. The results suggest that the proximal limit of the limb regenerate is determined by level-specific properties of the limb cells but that these properties allow for interactions leading to regulation when different levels of stump and blastema are brought together.     

OBSERVATIONS ON SUPERNUMERARY HEAD FORMATION INDUCED BY LITHIUM CHLORIDE TREATMENT IN THE REGENERATING HYDRA, PELMATOHYDRA ROBUSTA

Lithium chloride treatment of hydras cut just proximal to the tentacle circle and just distal to the budding region induces a supernumerary head at the proximal cut surface. Such a supernumerary head does not appear in the normal course of regeneration. The bipolar hydra thus formed persists for several weeks and later separates to form two normal individuals. The supernumerary head is not formed at the proximal cut surface when the hydra is transected just distal to the budding zone and the distal portion is allowed to regenerate in the Li-containing medium. LiCl has a slight inhibitory effect on the regeneration of hypostomes or tentacles when the animal is cut at the base of the hypostome.     

Spine motility. Phenomenology,mechanisms, and function

Throughout the history of neuroscience, dendritic spines have been considered stable structures, but in recent years, imaging techniques have revealed that spines are constantly changing shape. Spine motility is difficult to categorize, has different forms, and possibly even represents multiple phenomena. It is influenced by synaptic transmission, intracellular calcium, and a multitude of ions and other molecules. An actin-based cascade mediates this phenomenon, and while the precise signaling pathways are still unclear, the Rho family of GTPases could well be a "common denominator" controlling spine morphology. One role of spine motility might be to enable a searching function during synaptogenesis, allowing for more efficacious neuronal connectivity in the neuronal thicket. This idea revisits concepts originally formulated by Cajal, who proposed over a hundred years ago that spines might help to increase and modify synaptic connections.     

Spine-neck geometry determines NMDA receptor-dependent Ca2+ signaling in dendrites

Increases in cytosolic Ca2+ concentration ([Ca2+]i) mediated by NMDA-sensitive glutamate receptors (NMDARs) are important for synaptic plasticity. We studied a wide variety of dendritic spines on rat CA1 pyramidal neurons in acute hippocampal slices. Two-photon uncaging and Ca2+ imaging revealed that NMDAR-mediated currents increased with spine-head volume and that even the smallest spines contained a significant number of NMDARs. The fate of Ca2+ that entered spine heads through NMDARs was governed by the shape (length and radius) of the spine neck. Larger spines had necks that permitted greater efflux of Ca2+ into the dendritic shaft, whereas smaller spines manifested a larger increase in [Ca2+]i within the spine compartment as a result of a smaller Ca2+ flux through the neck. Spine-neck geometry is thus an important determinant of spine Ca2+ signaling, allowing small spines to be the preferential sites for isolated induction of long-term potentiation.     

Ca(2+) signaling in dendritic spines

Dendritic spines are cellular microcompartments that are isolated from their parent dendrites and neighboring spines. Recently, imaging studies of spine Ca(2+) dynamics have revealed that Ca(2+) can enter spines through voltage-sensitive and ligand-activated channels, as well as through Ca(2+) release from intracellular stores. Relationships between spine Ca(2+) signals and induction of various forms of synaptic plasticity are beginning to be elucidated. Measurements of spine Ca(2+) concentration are also being used to probe the properties of single synapses and even individual calcium channels in their native environment.     

A complete styginid trilobite from the Ordovician of Sweden

Styginidae are a small group of trilobite species, which are usually rare and most of which are incompletely known. Here we describe a complete specimen of Raymondaspis grandigena n.sp. from the Middle Ordovician (Darriwilian, upper Arenig) of Sweden. Among the group it has an unusual combination of exceptionally large genal spines, a thorax with notably short pleural spines in the anterior tergites, and a wide concave pygidial margin. The hypostome is documented for the first time in situ in a styginid, and its attachment can be best described as semi-impendent.     

Cell Surface Heparan Sulfate Proteoglycan Syndecan-2 Induces the Maturation of Dendritic Spines in Rat Hippocampal Neurons

Dendritic spines are small protrusions that receive synapses, and changes in spine morphology are thought to be the structural basis for learning and memory. We demonstrate that the cell surface heparan sulfate proteoglycan syndecan-2 plays a critical role in spine development. Syndecan-2 is concentrated at the synapses, specifically on the dendritic spines of cultured hippocampal neurons, and its accumulation occurs concomitant with the morphological maturation of spines from long thin protrusions to stubby and headed shapes. Early introduction of syndecan-2 cDNA into immature hippocampal neurons, by transient transfection, accelerates spine formation from dendritic protrusions. Deletion of the COOH-terminal EFYA motif of syndecan-2, the binding site for PDZ domain proteins, abrogates the spine-promoting activity of syndecan-2. Syndecan-2 clustering on dendritic protrusions does not require the PDZ domain-binding motif, but another portion of the cytoplasmic domain which includes a protein kinase C phosphorylation site. Our results indicate that syndecan-2 plays a direct role in the development of postsynaptic specialization through its interactions with PDZ domain proteins.