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PubMedDate not supplied

Caudal and even-skipped in the annelid Platynereis dumerilii and the ancestry of posterior growth.

In order to address the question of the conservation of posterior growth mechanisms in bilaterians, we have studied the expression patterns of the orthologues of the genes caudal, even-skipped, and brachyury in the annelid Platynereis dumerilii. Annelids belong to the still poorly studied third large branch of the bilaterians, the lophotrochozoans, and have anatomic and developmental characteristics, such as a segmented body plan, indirect development through a microscopic ciliated larva, and building of the trunk through posterior addition, which are all hypothesized by some authors (including us) to be present already in Urbilateria, the last common ancestor of bilaterians. All three genes are shown to be likely involved in the building of the anteroposterior axis around the slit-like amphistomous blastopore as well as in the patterning of the terminal anus-bearing piece of the body (the pygidium). In addition, caudal and even-skipped are likely involved in the posterior addition of segments. Together with the emerging results on the conservation of segmentation genes, these results reinforce the hypothesis that Urbilateria had a segmented trunk developing through posterior addition.

Animals↗
PubMedDate not supplied

The fine structure of the gamont of Pterospora floridiensis (Apicomplexa: Eugregarinida).

Transmission electron microscopy of the gamont stage of Pterospora floridiensis has revealed a number of features. The gamont's surface varies from smooth to crenulate, with numerous pockets and folds. The pellicle is composed of an outer membrane, a middle lucent region, and an inner dense layer comprised of two tightly appressed membranes. Short ridges on the pellicle are 200-300+ nm long, 75-100 nm wide, and have a height of approximately 50 nm. The thickness of the pellicle is 100 nm when measured from the inner membrane to the top of a ridge. The ridges are formed by the plasma membrane and an underlying structure that is circular in cross-section. The surface folds and the pellicular ridges are distributed over the soma and the cell's unusual branching arms, though both are reduced near the junction between two gamonts in syzygy, and are absent at the central area of the junctional site. The cell has numerous active Golgi complexes associated with vesicles, as well as scattered dense mitochondria, lipid droplets, and paraglycogen granules. The nucleus has a large (13 microm) endosome, eccentrically located, and peripheral chromatin along the inner nuclear membrane.

Animals↗
PubMedDate not supplied

Comparative surface morphology of marine coelomic gregarines (Apicomplexa, Urosporidae): Pterospora floridiensis and Pterospora schizosoma.

Two species in the aseptate gregarine genus Pterospora from the Pacific and Gulf coasts were analyzed by scanning electron microscopy, which revealed characteristics not reported in other gregarines. The gamonts of these species had branching trunks that ended in terminal digits, and both species moved by cytoplasmic streaming and peristalsis. Pterospora floridiensis had surface pits and tracts of parallel ridges that bended and connected with one another. Pterospora schizosoma had irregular-shaped surface swellings that were usually arranged in rosette patterns. These unique surface features have not been reported for other gregarines, and are strikingly different from the surface features of many septate and aseptate gregarines that inhabit the intestinal lumena of their hosts and move by gliding. The correlation of Pterospora's unique pellicular features to the habitat and cytoplasmic streaming characteristic of the genus may be significant, and may reflect an adaptation for development in coelomic environments.

Animals↗
PubMed2005

Solution structure and internal dynamics of NSCP, a compact calcium-binding protein.

The solution structure of Nereis diversicolor sarcoplasmic calcium-binding protein (NSCP) in the calcium-bound form was determined by NMR spectroscopy, distance geometry and simulated annealing. Based on 1859 NOE restraints and 262 angular restraints, 17 structures were generated with a rmsd of 0.87 A from the mean structure. The solution structure, which is highly similar to the structure obtained by X-ray crystallography, includes two open EF-hand domains, which are in close contact through their hydrophobic surfaces. The internal dynamics of the protein backbone were determined by studying amide hydrogen/deuterium exchange rates and 15N nuclear relaxation. The two methods revealed a highly compact and rigid structure, with greatly restricted mobility at the two termini. For most of the amide protons, the free energy of exchange-compatible structural opening is similar to the free energy of structural stability, suggesting that isotope exchange of these protons takes place through global unfolding of the protein. Enhanced conformational flexibility was noted in the unoccupied Ca2+-binding site II, as well as the neighbouring helices. Analysis of the experimental nuclear relaxation and the molecular dynamics simulations give very similar profiles for the backbone generalized order parameter (S2), a parameter related to the amplitude of fast (picosecond to nanosecond) movements of N(H)-H vectors. We also noted a significant correlation between this parameter, the exchange rate, and the crystallographic B factor along the sequence.

Amides↗
PubMed2005

Origin and properties of cytoplasmic and mitochondrial isoforms of taurocyamine kinase.

Taurocyamine kinase (TK) is a member of the highly conserved family of phosphagen kinases that includes creatine kinase (CK) and arginine kinase. TK is found only in certain marine annelids. In this study we used PCR to amplify two cDNAs coding for TKs from the polychaete Arenicola brasiliensis, cloned these cDNAs into the pMAL plasmid and expressed the TKs as fusion proteins with the maltose-binding protein. These are the first TK cDNA and deduced amino acid sequences to be reported. One of the two cDNA-derived amino acid sequences of TKs shows a high amino acid identity to lombricine kinase, another phosphagen kinase unique to annelids, and appears to be a cytoplasmic isoform. The other sequence appears to be a mitochondrial isoform; it has a long N-terminal extension that was judged to be a mitochondrial targeting peptide by several on-line programs and shows a higher similarity in amino acid sequence to mitochondrial creatine kinases from both vertebrates and invertebrates. The recombinant cytoplasmic TK showed activity for the substrates taurocyamine and lombricine (9% of that of taurocyamine). However, the mitochondrial TK showed activity for taurocyamine, lombricine (30% of that of taurocyamine) and glycocyamine (7% of that of taurocyamine). Neither TK catalyzed the phosphorylation of creatine. Comparison of the deduced amino acid sequences of mitochondrial CK and TK indicated that several key residues required for CK activity are lacking in the mitochondrial TK sequence. Homology models for both cytoplasmic and mitochondrial TK, constructed using CK templates, provided some insight into the structural correlation of differences in substrate specificity between the two TKs. A phylogenetic analysis using amino acid sequences from a broad spectrum of phosphagen kinases showed that annelid-specific phosphagen kinases (lombricine kinase, glycocyamine kinase and cytoplasmic and mitochondrial TKs) are grouped in one cluster, and form a sister-group with CK sequences from vertebrate and invertebrate groups. It appears that the annelid-specific phosphagen kinases, including cytoplasmic and mitochondrial TKs, evolved from a CK-like ancestor(s) early in the divergence of the protostome metazoans. Furthermore, our results suggest that the cytoplasmic and mitochondrial isoforms of TK evolved independently.

Amino Acid Sequence↗
PubMed2006

Novel dissociation mechanism of a polychaetous annelid extracellular haemoglobin.

The extracellular haemoglobin of the marine polychaete, Arenicola marina, is a hexagonal bilayer haemoglobin of approximately 3600 kDa, formed by the covalent and noncovalent association of many copies of both globin subunits (monomer and trimer) and nonglobin or 'linker' subunits. In order to analyse the interactions between globin and linker subunits, dissociation and reassociation experiments were carried out under whereby Arenicola hexagonal bilayer haemoglobin was exposed to urea and alkaline pH and the effect was followed by gel filtration, SDS/PAGE, UV-visible spectrophotometry, electrospray-ionization MS, multiangle laser light scattering and transmission electron microscopy. The analysis of Arenicola haemoglobin dissociation indicates a novel and complex mechanism of dissociation compared with other annelid extracellular haemoglobins studied to date. Even though the chemically induced dissociation triggers partial degradation of some subunits, spontaneous reassociation was observed, to some extent. Parallel dissociation of Lumbricus haemoglobin under similar conditions shows striking differences that allow us to propose a hypothesis on the nature of the intersubunit contacts that are essential to form and to hold such a complex quaternary structure.

Animals↗
PubMed2006

Isolation of a cDNA encoding a protease from Perinereis aibuhitensis Grube.

The cDNA encoding a protease of Perinereis aibuhitensis Grube (PPA) was cloned. The deduced amino acid sequence analysis showed that the protein had 49% identity to the C-terminal amino acid 169-246 of serine protease of Heterodera glycines. Northern blotting analysis indicated that the cDNA could hybridize with mRNA of approximately 260 bases isolated from the marine earthworm. The cDNA was amplified by polymerase chain reaction and cloned into pMAL-p2 to construct expression vector pMAL-PPA. pMAL-PPA was introduced into Escherichia coli BL21(DE3) and overexpression of PPA fused with maltose binding protein was achieved by isopropyl-beta-D-thiogalactopyranoside induction. The fusion protein was purified by affinity chromatography on an amylose resin column and ion-exchange chromatography on a diethylaminoethyl-Sepharose 4B column. Rabbits were immunized with the purified protein and antiserum was prepared. The antibody could react with a protein of approximately 9 kDa extracted from the marine earthworm as shown by Western blotting analysis. The activity analysis of the recombinant PPA suggested that it was probably a plasminogen activator.

Amino Acid Sequence↗
PubMed1975

The interactions of calcium with mpyxicola giant axons and a description in terms of a simple surface charge model.

1. Myxicola giant axons were examined under voltage clamp in solutions with [Ca2+] ranging from 2 to 200 mM. 2. The magnitude of the shifts in the Na and K conductance-voltage curves, as well as membrane rate constants, caused by changes IN [Ca22+] were comparable and consistent with a model in which there exists a negative surface charge density of -0.013 charges/A-2, but there is no significant binding of divalent cations to the external membrane surface. 3. There was no effect of equimolar substitution of magnesium for Ca on the positions of the conductance-voltage curves along the voltage axis, consistent with the above conclusion. 4. Ca2+ has no effect on the shape of the steady-state Na inactivation relation but simply causes a translation along the voltage axis. 5. It is concluded that a simple surface charge model in which divalent cations do not bind is adequate for Myxicola axons, and that there is no evidence to support a specific involvement of Ca with gating processes.

Animals↗
PubMed1975

Axoplasm architecture and physical properties as seen in the Myxicola giant axon.

A technique is described for extracting axoplasm from the giant axon of a marine worm, Myxicola infundibulum. The operation can be completed in 10 sec. 2. Axoplasm is pulled from the axon of a living worm as a long, clear cylinder, up to 35 cm long and 70 mg wet weight. The worm regenerates a new giant axon in about 4 months. 3. Myxicola axoplasm is a gel, 87% water, held together by protein neurofilaments. It contains small amounts of mitochondria and vesicles, but no detectable microtubules. 4. The internal structure of the gel is superficially similar to that of yarn. Closer inspection with light and electron microscopy, and X-ray diffraction, show it to be organized in a hierarchy of helical forms. Squid giant axons have a similar structure. 5. Initial estimates of the bulk physical properties of extracted Myxicola axoplasm give: breaking strength, 1400 g/cm2; specific gravity, 1-05 g/cm3; birefringence, 1-6 X 10(-4); index of refraction, 1-351; resistivity, 57 omega cm. These average values are shown to be compatible with the observed structure and composition. 6. Despite its mechanical strength, the axoplasm gel is so hydrated that Na+, K+ and homarine diffuse through it at rates approaching those in free solution. Fewer than about 5% of each of these ions are tightly bound to the gel. 7. It is argued that (a) the structure and physical properties of Myxicola axoplasm are representative of those in other axons, (b) the compound helix architecture results from twist of parallel, cross-linked fibrous proteins, and (c) this sturcture serves as a flexible internal skeleton for nerve cell processes.

Animals↗
PubMed1975

Axoplasm chemical composition in Myxicola and solubility properties of its structural proteins.

The chemical composition of axoplasm extracted from the giant axon of Myxicola infundibulum has been analysed, and some of the factors which disperse its gel structure have been identified. 2. The axoplasm contains about 3-6% protein, and 0-12% lipid. It is isosmotic with sea water and has a pH near 7-0. 3. Inorganic ions in extracted axoplasm include: Na+, 13m-mole/kg wet wtl; K+, 280; Cl-, 24; Ca2+, 0-3; Mg2+, 3. 4. Free organic ions in axoplasm include: gly, 180 m-mole/kg wet st.; cysteic acid, 120; asp, 75; glu, 10; ala, 7; tau, 5; thr, 2; gln and ser, trace; homarine, 63; isethionate, 0. 5. The gel structure is dispersed by solutions containing 1--10 mM-Ca2+, because this ion activates an endogenous protease. The gel can also be dispersed without proteilysis by solutions containing 0-5 M-KCl, or 0-5 M guanidine hydrochloride, or 3-5 M urea, all of which break down neurofilaments. 6. It is argued that many aspects of the composition and dispersal properties of Myxicola axoplasm are similar to those in other axons.

Amino Acids↗
PubMed1977

Changes in excitability of the cell membrane during 'differentiation without cleavage' in the egg of the annelid, Chaetopterus pergamentaceus.

1. The egg of the polychaete, Chaetopterus pergamentaceus, differentiates parthenogenetically without cleavage after 1 hr in a high K+ solution. The changes in the electrical properties of the membrane during differentiation have been investigated. 2. The treatment with the K solution for 40-60 min made unfertilized eggs become amoeboid cells in 4-5 hr and finally ciliated unicellular embryos in 14-16 hr. 3. In the untreated egg the action potential is Ca dependent and no Na component is found. The steady-state current-voltage relation has a marked inward rectification and shows a less marked outward rectification. 4. There are no significant changes in these properties of the cell membrane immediately after 40-60 min K treatment. 5. In the amoeboid cell stage (4-5 hr) the outward rectification increases significantly. 6. In the ciliated unicellular embryo the action potential is Ca and Na dependent. 7. The result suggests that Ca channels are present in the egg initially, K channels appear next and Na channels appear later.

Action Potentials↗
PubMed1978

Uptake and binding of calcium by axoplasm isolated from giant axons of Loligo and Myxicola.

1. Axoplasm isolated from giant axons of the squid Loligo and of the polychaete worm Myxicola continues to bind Ca and maintain an ionized Ca concentration close to 0.1 microgram which is similar to that seen in intact axons. 2. Injection of Ca into isolated axoplasm only produces a transient rise in ionized Ca showing that axoplasm can buffer a Ca challenge. 3. In order to characterize the Ca-binding systems isolated axoplasm was placed in small dialysis tubes and exposed to a variety of artificial axoplasms containing 45Ca. 4. In the presence of ATP, orthophosphate and succinate, Ca uptake appreciable and after 4 hr exposure of Loligo axoplasm to 0.1 microgram-Ca, approximately 100 mumole Ca/kg axoplasm was bound. Binding could be divided operationally into two distinct processes, one that requires ATP or succinate togeth with orthophosphate and is blocked by cyanide and oligomyocin, and one that is unaffected by these reagents. 5. Energy-dependent binding has a large capacity, but a rather low affinity for Ca, being half-maximal between 20 and 60 microgram-Ca. In Loligo, its properties closely parallel those of a crude mitochondrial preparation isolated from axoplasm; but there are some interesting differences in Myxicola. Energy-independent binding is half-maximal at ionized Ca concentrations between 80 and 160 nM but is readily saturated and has a capacity of 6-60 mumole/kg axoplasm. 6. Ca binding by Loligo is greatest in media containing roughly physiological concentrations of K and is reduced by isosmotic replacement of K by Na. This effect seems to be confined to the energy-dependent, presumed mitochondrial, component of binding. 7. Ca binding by Loligo axoplasm is reduced by both La and Mn ions.

Adenosine Triphosphate↗
PubMed1978

Combined voltage-clamp and dialysis of Myxicola axons: behaviour of membrane asymmetry currents.

4. A new technique for the simultaneous internal dialysis and voltage-clamp of Myxicola axons is described and shown to control the internal composition of the axon adequately. 2. The permeability ratio (PNa/PK) of the sodium channel is 15.5 in axons dialysed with sodium-free solutions, somewhat higher than observed in perfused axons. 3. Asymmetry currents are easily recorded in dialysed Myxicola axons. At 4--5 degrees C for pulse durations sufficiently short Qon = Qoff with a maximum charge displacement of 10 nC/cm2 and half the charge being displaced by a step to -32 mV. Maximum slope of the Q(V) curve is 15 mV/e-fold change in charge displaced. The time constant tau on reaches a maximum of 325 microseconds at a potential of -23 mV. 4. The time course of sodium activation cannot be adequately accounted for by (Q/Q infinity) X using any single value of X for potentials between -40 and 40 MV. 5. Both asymmetry currents and INa are inactivated by the same amount when Myxicola axons are repetitively depolarized at frequencies from 0.1 to 50 Hz.

Animals↗
PubMed1979

Immobilization of intramembrane charge in Myxicola giant axons.

1. Immobilization of gating charge was examined in Myxicola giant axons dialysed with Cs+. 2. With increasing pulse durations the ratio QOFF/QON decreases to as little as 0.25 with a time constant of 3.2 msec determined from composite data. Na inactivation time constants measured in the same axons ranged from 0.8 to 1.5 msec. A slow component of QOFF tends to appear as QOFF/QON decreases. 3. Both QON and QOFF may be decreased by a prepulse with no change in their time course. In this case the time course of the decrease is similar to that observed for INA. 4. The normalized steady-state charge immobilization curve is shifted in the depolarized direction by 15--20 mV from the normalized Na inactivation curve.

Animals↗
PubMed1980

Calcium efflux from Myxicola giant axons: effects of extracellular calcium and intracellular EGTA.

1. (45)Ca efflux was examined in Myxicola giant axons injected with (45)CaCl(2) or various concentrations of (45)Ca/EGTA buffers. In axons injected with (45)CaCl(2), the Ca(o)-dependent Ca efflux in 1 mM-Ca(o) was about half that in 10 mM-Ca(o).2. Axons injected with (45)Ca/EGTA buffers consistently showed two types of results: in one type (B type), K((1/2)) for Ca(o) activation was less than 1 mM-Ca(o). In the other type of result (A type), there was an additional Ca activation of Ca efflux. This additional efflux exhibited a linear dependence on Ca(o) when the Ca(o) values ranged between 1 mM-Ca(o) and 10 mM-Ca(o).3. The B-type result remained unchanged when the injected Ca/EGTA concentrations were varied. The A type result, however, changed as a function of Ca/EGTA(i) in the following way: (a) at a constant ratio of Ca/EGTA(i) = 8/10, the megnitude of the linear component of the Ca(o)-activated Ca efflux was reduced by increasing the intracellular concentration of (Ca/EGTA) buffer; and (b) at a ratio Ca/EGTA = 1/10, the linear component of the Ca(o)-activated Ca efflux appeared to acquire a slower time response to changes in Ca(o).4. Na(o) acts synergistically with Ca(o) to produce the linear component of the Ca-activated Ca efflux seen in the A type result.5. With axons containing (45)Ca/EGTA buffers (total EGTA(i) = 1 mM), changing the Ca/EGTA ratio by repetitive injections of CaCl(2) did not increase (45)Ca efflux by as great an amount as would be predicted if Ca(i) (2+) were controlled by the EGTA buffer alone.6. Ca(i) (2+) (measured by arsenazo III absorbance) is influenced by Ca(o) irrespective of the presence of 1 mM-EGTA buffer inside the axon. There was a variability in the sensitivity of Ca(i) to Ca(o) that resembled the variability found in (45)Ca efflux measurements.7. (45)Ca influx is not affected by the concentration of Ca/EGTA buffer injected into the cell and appears to be only slightly, if at all, affected by increasing ionized Ca(i) (2+) from 0.016 to 0.56 muM in the injection medium.8. These results are consistent with the interpretation that the Ca efflux system of the Myxicola giant axon, or something controlling it, can exist in more than one state. One of these states, which exhibited a large Ca(o)-dependent Ca efflux, may represent axons in which Ca(i) is poorly controlled by the natural endogenous Ca buffers.

Animals↗
PubMed1981

Inactivation in Myxicola giant axons responsible for slow and accumulative adaptation phenomena.

1. The action potential in Myxicola giant axons is abolished if the nerve is stimulated at frequencies higher than about 5 sec-1. At 1 sec-1 the magnitude of the action potential is not maintained upon sequential stimulation but decreases until the response is abolished. 2. The behaviour of the ionic currents underlying the action potential was studied with voltage-clamp techniques to find the origin of such adaptation. These studies showed a frequency-dependent decline of the sodium currents. 3. The decline in the Na currents upon repetitive depolarization is shown to be due to a decrease in the Na conductance and not to change in driving force. 4. An analysis of the effects of conditioning depolarizations on the Na current during a depolarizing test pulse demonstrates that in a single short depolarization (less than 10 msec) 15% of the Na conductance enters an inactivated state from which recovery is very slow. Upon repetitive depolarizations the amount of Na conductance available accumulates in this slowly recovering inactivated state. 5. The data are explained by proposing that every time the membrane is depolarized open channels undergo one of two competing reactions. Open channels enter either the traditional inactivated state described by Hodgkin & Huxley (1952b) from which recovery is fast (a few milliseconds) or an inactivated state from which recovery is very slow (seconds). In Myxicola, only 15% of open channels enter the later inactivated state in a single depolarization. Upon repetitive depolarizations, however, the fraction in this state accumulates if the frequency of pulsing is faster than the rate of recovery. 6. Axons in which the amount of open channels entering the slowly recovering inactivated state is significant, such as in Myxicola, have thus a system capable of storing the previous activity of the axon for periods of seconds or minutes.

Action Potentials↗