Paddle-like Structure Research Articles

CTENO64 Is Required for Coordinated Paddling of Ciliary Comb Plate in Ctenophores.

Ctenophores, or comb jellies, are one of the earliest branching basal metazoan groups, whose phylogenetic position continues to be controversial. They have eight rows of iridescent structures, called comb plates, which are huge multiciliated paddle-like structures used for locomotion and uniquely found in this group of animals [1]. Despite a number of morphological and physiological studies over the past 50 years, the molecular nature of comb plates remains completely unknown. Here, we identified a protein CTENO64 that is specifically localized in the comb plates. This protein is only found in ctenophores and not in other animals or eukaryotic species that possess multiciliary cells or tissues. It is localized to regions, called compartmenting lamella (CL), which are uniquely seen in ctenophore multicilia, connecting adjacent cilia in the comb plates. Knockdown of the CTENO64 gene did not affect the formation of comb plates but caused the loss or misformation of CLs and the disruption of ciliary orientation, resulting in aberrant and non-planar waveforms in the mid-distal region of the comb plates. We propose that CLs have been convergently acquired in ctenophores to overcome the hydrodynamic constraints of possessing extremely long multicilia. Our findings provide the initial step in unveiling the molecular structure and evolutionary significance of ciliary comb plates and shed light not only on the hidden biology of ctenophores but also on the unique evolutionary pathway of these animals. VIDEO ABSTRACT.

Brief Local Application of Progesterone via a Wearable Bioreactor Induces Long-Term Regenerative Response in Adult Xenopus Hindlimb

SUMMARYThe induction of limb repair in adult vertebrates is a pressing, unsolved problem. Here, we characterize the effects of an integrated device that delivers drugs to severed hindlimbs of adult Xenopus laevis, which normally regenerate cartilaginous spikes after amputation. A wearable bioreactor containing a silk protein-based hydrogel that delivered progesterone to the wound site immediately after hindlimb amputation for only 24 hr induced the regeneration of paddle-like structures in adult frogs. Molecular markers, morphometric analysis, X-ray imaging, immunofluorescence, and behavioral assays were used to characterize the differences between the paddle-like structures of successful regenerates and hypomorphic spikes that grew in untreated animals. Our experiments establish a model for testing therapeutic cocktails in vertebrate hindlimb regeneration, identify pro-regenerative activities of progesterone-containing bioreactors, and provide proof of principle of brief use of integrated device-based delivery of small-molecule drugs as a viable strategy to induce and maintain a long-term regenerative response.

The internal structure of the pallets of Nototeredo norvagica and Psiloteredo megotara (Bivalvia: Teredinidae): implications for subfamilial allocations

The Teredinidae possess specialised calcareous paddle-like structures, the pallets, which flank the siphons. The external segmentation/non-segmentation of the pallets is used as the main diagnostic character to distinguish between the Teredininae (non-segmented pallet line) and the Bankiinae (segmented pallet line). The internal segmentation of the pallets has, however, seldom been accessed. Therefore, in the present study, the internal structure of the pallets of Psiloteredo megotara (Teredininae) and Nototeredo norvagica (Bankiinae) was analysed using scanning electron microscopy. Pallets of P. megotara were segmented, in a fashion similar to those of N. norvagica, rather than lacking true segmentation as had been reported previously. This finding, affecting a key character state, supports results from previous molecular work and shows the need for further work to ascertain the valid compositions of the Teredininae and Bankiinae.

Two new cis-Andean species of the South American catfish genus Megalonema allied to trans-Andean Megalonema xanthum, with description of a new subgenus (Siluriformes: Pimelodidae)

A revised diagnosis of the pimelodid catfish genus Megalonema is given based on synapomorphic features of the Weberian complex and gas bladder. Megalonema xanthum from the Magdalena River is redescribed. Two new cis-Andean species of Megalonema are described, M. amaxanthum n. sp. from the Amazon River basin, and M. orixanthum n. sp. from the Orinoco River basin. These three species are differentially diagnosed by shape and size of the supraoccipital posterior process, adipose-fin shape, vertebral counts, eye size, premaxillary bone shape and dentition, length of the anal-fin base, width between the posterior nostrils and presence/absence of dentations on the pectoral spine. Eretmomegalonema new subgenus is established for M. xanthum, M. amaxanthum and M. orixanthum and supported by the uniquely synapomorphic paddle-like structure of its pelvic fin and hypertrophied basipterygium. Unambiguous synapomorphies indicate a sister-group relationship between M. amaxanthum and M. orixanthum, with M. xanthum basal to this pair. This topology is congruent with the Neogene origins of separate Magdalena, Amazon and Orinoco basins suggesting vicariant control of diversification of Eretmomegalonema.

Crystal Structure of a TOG Domain: Conserved Features of XMAP215/Dis1-Family TOG Domains and Implications for Tubulin Binding

Members of the XMAP215/Dis1 family of microtubule-associated proteins (MAPs) are essential for microtubule growth. MAPs in this family contain several 250 residue repeats, called TOG domains, which are thought to bind tubulin dimers and promote microtubule polymerization. We have determined the crystal structure of a single TOG domain from the Caenorhabditis elegans homolog, Zyg9, to 1.9 A resolution, and from it we describe a structural blueprint for TOG domains. These domains are flat, paddle-like structures, composed of six HEAT-repeat elements stacked side by side. The two wide faces of the paddle contain the HEAT-repeat helices, and the two narrow faces, the intra- and inter-HEAT repeat turns. Solvent-exposed residues in the intrarepeat turns are conserved, both within a particular protein and across the XMAP215/Dis1 family. Mutation of some of these residues in the TOG1 domain from the budding yeast homolog, Stu2p, shows that this face indeed participates in the tubulin contact.

Interfacial Tryptophan Residues: A Role for the Cation- π Effect?

Integral membrane proteins are characterized by having a preference for aromatic residues, e.g., tryptophan (W), at the interface between the lipid bilayer core and the aqueous phase. The reason for this is not clear, but it seems that the preference is related to a complex interplay between steric and electrostatic forces. The flat rigid paddle-like structure of tryptophan, associated with a quadrupolar moment (aromaticity) arising from the π-electron cloud of the indole, interacts primarily with moieties in the lipid headgroup region hardly penetrating into the bilayer core. We have studied the interaction between the nitrogen moiety of lipid molecule headgroups and the π-electron distribution of gramicidin (gA) tryptophan residues ( W 9 , W 11 , W 13 , and W 15 ) using molecular dynamics (MD) simulations of gA embedded in two hydrated lipid bilayers composed of 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE) and 1-palmitoyl-2-oleoylphosphatidyl-choline (POPC), respectively. We use a force field model for tryptophan in which polarizability is only implicit, but we believe that classical molecular dynamics force fields are sufficient to capture the most prominent features of the cation- π interaction. Our criteria for cation- π interactions are based on distance and angular requirements, and the results from our model suggest that cation- π interactions are relevant for W PE 11 , W PE 13 , W PE 15 , and, to some extent, W PC 11 and W PC 13 . In our model, W 9 does not seem to engage in cation- π interactions with lipids, neither in POPE nor POPC. The criteria for the cation- π effect are satisfied more often in POPE than in POPC, whereas the H-bonding ability between the indole donor and the carbonyl acceptor is similar in POPE and POPC. This suggests an increased affinity for lipids with ethanolamine headgroups to transmembrane proteins enriched in interfacial tryptophans.

Binding of Co3+ and within a Pyridine-cored Molecular Cleft

When the novel pyridine-2,6-dicarboxylic acid bis[(quinolin-8-ylmethyl)amide] (PDQA) is treated with CoCl2 a 1:1 complex [(PDQAH2)][CoIICl4] (2), is formed. Treatment of 2 with NaNO2 results in oxidation of the to CoIII affording [(PDQA-H)CoIII(NO2)2] (3) whereas under basic conditions a 2:1 (ligand:CoIII) paddle-like structure [CoIII(PDPA-2H)2K(H2O)2(CH3OH)1]·(H2O)2 (1) is obtained.

Effects of the actin-stabilizing drug, jasplakinolide, on pigment granule motility in isolated retinal pigment epithelial (RPE) cells of green sunfish, Lepomis cyanellus.

The retinal pigment epithelium (RPE) of teleosts contains pigment granules that migrate in response to changes in light condition. Dissociated, cultured RPE cells in vitro can be triggered to aggregate or disperse pigment granules by the application of cAMP or dopamine, respectively. Previous research using the actin-disrupting drug, cytochalasin D, suggested that pigment granule motility is actin dependent. To further examine the role of actin in pigment granule motility, we tested the effects of the actin-stabilizing drug, jasplakinolide, on pigment granule motility. Pigment granules in previously dispersed RPE cells remained dispersed after jasplakinolide exposure (0.1-1 microM), but the drug halted movement of most pigment granules and stimulated rapid bi-directional movements in a small subset of granules. Jasplakinolide also blocked net pigment granule aggregation and interfered with the maintenance of full aggregation. Although jasplakinolide did not block pigment granule dispersion, it did alter the motility of dispersing granules compared to control cells; rather than the normal saltatory, primarily centrifugal movements, granules of jasplakinolide-treated cells demonstrated slow, creeping centrifugal movements and more rapid bi-directional movements. Jasplakinolide also altered cell morphology; the length and thickness of apical projections increased, and enlarged, paddle-like structures, which contained F-actin appeared at the tips of projections. Actin antibody labeling of jasplakinolide-treated cells revealed a more reticulated network of actin compared to antibody-labeled control cells. These results indicate that jasplakinolide-induced disruption of the actin network compromises normal pigment granule dispersion and aggregation in isolated RPE cells, thus providing further evidence that these movements are actin dependent.

Highly active neuromuscular system in developing lobsters with programmed obsolescence.

The primary locomotory apparatus in the three larval stages of the lobster, Homarus americanus, are paddlelike structures on the thoracic appendages called exopodites, which beat almost continuously. Consequently their power and return-stroke muscles are examples of highly active but short-lived neuromuscular systems. The muscles, which are well vascularized, are of the fast type with 2-3-micron sarcomere lengths and 6 thin filaments surrounding a thick one. The most striking feature, however, is the large volume of mitochondria making up 40-50% of the fiber. They appear as simple cylinders packed several layers deep along the periphery of the fiber and as large, multibranched forms distributed throughout the fiber and subdividing it into smaller units. The motor innervation to the return-stroke muscle is via 3 excitatory axons, which generate large junctional potentials and twitch contractions. The muscle is densely populated with large neuromuscular synapses, most of which have a well-defined active site or dense bar denoting the site of transmitter release. Altogether this motor system is specialized for prolonged activity. Atrophy of the neuromuscular system occurs by the late larval third stage. The muscle fibers lose their identity, fuse, and become vacuolated. The myofibrils condense and erode and the mitochondria are lost. Atrophy of motor innervation is gradual with individual axons dropping out. The largest axon providing most of the innervation is the first to degenerate. Early degenerative changes affect the axon and neuromuscular terminals but not the synaptic contacts, dense bars, and vesicles, which appear intact. Continued atrophy in the postlarval fourth stage reduces the exopodites to vestiges. Thus the return-stroke muscle of the larval exopodites in which muscle fiber and motoneurons are identifiable permits study of the interaction between a neuron and its target muscle undergoing programmed obsolescence.

Cell density and cell division in the early morphogenesis of the chick wing.

THE early development of the chick wing involves cell differentiation, pattern formation and growth1. In general terms, its morphogenesis can be seen in terms of how the growth of the mesenchyme and ectoderm is controlled, so that the very simple initial protrusion is transformed into an elongated paddle-like structure. At the same time a spatial pattern of differentiation must be specified within the mesenchyme, the cells forming cartilage and muscle so that the major skeletal and muscular features are laid down. In a previous paper2 we described the changing pattern of the distribution of mitoses in the mesenchyme. We found that there was an overall fall in mitotic index from early stages (18–19 Hamburger-Hamilton) but that this occurred more rapidly in the proximal regions after about stage 23 so that a graded proximo-distal increase in mitotic index became established. We also suggested that the overall form was determined by the ectoderm and not the mesenchyme. This raised specific problems about the control of growth of the mesenchyme: we could not account for the observed distribution of mitoses but wondered whether this involved a temporal programme or was related to positional information. Our investigations of the so-called mesenchymal condensations which are supposed to be the prelude to cartilage formation3 have led to detailed analysis of cell density during early morphogenesis. We show here that the cell density varies in a very regular manner and is closely correlated with mitotic index: mitotic index is inversely proportional to cell density. This finding is not only important in its own right because it may be the first demonstration of density dependent growth control4in vivo, but because it provides a new mechanism for the control of growth and pattern formation in limb morphogenesis.