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PubMed1994

Identification of two ets related genes in a marine worm, the polychaete annelid Nereis diversicolor.

The ETS family includes a growing number of transcription factors with a highly conserved DNA-binding domain, the ETS domain. We have used PCR amplification with degenerated oligonucleotides to isolate two putative ETS DNA-binding coding domains in a primitive form of coelomate, the polychaete annelid Nereis diversicolor. These sequences are highly related to the ETS and ERG groups of the ets gene family. For the erg sequence an adjacent region encoding for 91 amino acids has been characterized after library screening, and we show an expression in cells isolated from the coelomic cavity of the animal. A phylogenic analysis confirms that the ets-1/ets-2 and the erg/fli dichotomy arose specifically in the vertebrate lineage.

Amino Acid Sequence↗
PubMed1996

Nereis sarcoplasmic Ca2+-binding protein has a highly unstructured apo state which is switched to the native state upon binding of the first Ca2+ ion.

NSCP, a sarcoplasmic Ca2+/Mg2+-binding protein from Nereis diversicolor, shows an allosteric change during Ca2+ binding and a high positive cooperativity for Mg2+ binding. Here we report the results of CD and NMR experiments aiming to characterize the apo state and the Ca2+-induced conformational changes in this protein. Circular dichroism spectra of the apo form are indicative of a reduced helical structure. In contrast, NMR spectra show no element of regular secondary or tertiary structure. Addition of one Ca2+ determines large spectral changes bringing the molecule in a conformation which is very close to the native three Ca2+ state. Addition of the second and third Ca2+ shifts this equilibrium progressively towards the liganded conformation but affects only minimally the spectrum of the liganded species.

Animals↗
PubMed1983

Endocrine programmed development and reproduction in Nereis.

The pattern of cerebral endocrine activity in Nereis diversicolor is characterized by the maintenance of a high plateau of activity prior to, and during most of, the time occupied by gametogenesis. During the closing stages of the life cycle, the rate of secretion is progressively reduced, resulting in the production of a homogeneous population of gametocytes and subsequently in their final maturation. Secretion has been assayed in terms of the regeneration-promoting, maturation-inhibiting, and gametotrophic activities of the hormone. Assays involved transplantation of living brains, in some cases between animals at different stages of maturity, but evidence is presented that the activity of such brains reliably reflects their rate of secretion in situ. Cerebral control of growth and maturation is probably mediated by a single hormone, an ordered sequence of events occurring as different thresholds for hormone action are reached in turn.

Animals↗
PubMed1986

Subunit assembly of giant haemoglobin from the polychaete Tylorrhynchus heterochaetus.

The subunit assembly of the giant haemoglobin of the polychaete Tylorrhynchus heterochaetus is presented. Tylorrhynchus haemoglobin consists of two types of subunits: a "monomeric" chain I and a disulphide-bonded "trimer" of chains IIA, IIB and IIC. The molar ratio of the four constituent chains was determined by statistical comparison of the accurate amino acid composition calculated from the sequence of each chain and the observed composition measured by amino acid analysis of the whole molecule. On the basis of the molar ratio and the molecular weight of each chain, deduced from the amino acid sequence, a symmetrical model for the molecular assembly of the haemoglobin was constructed. The proposed model consists of four species of chains of 192 polypeptides and has a molecular weight of 3,275,808. The minimum structural entity is a "tetramer" consisting of the "monomeric" chain and the disulphide-bonded "trimer". Each chain contains one haem.

Amino Acid Sequence↗
PubMed1987

X-ray diffraction patterns from microtubules and neurofilaments in axoplasm.

Freshly extracted axoplasm from giant axons of the marine fan worm Myxicola infundibulum and the squid Loligo can be pulled into fibres that contain highly oriented cytoskeletal elements suitable for X-ray diffraction. A major advantage of studying axoplasmic components by this technique is that it allows essentially native structures and their interactions to be examined. We describe here the analyses of the X-ray diffraction patterns. We show that in Myxicola the pattern can be explained by diffraction from both neurofilaments and microtubules, whilst in Loligo the pattern arises solely from microtubules. At low resolution, X-ray patterns obtained from dehydrated axoplasmic microtubules resemble strongly the Fourier transforms generated from electron micrographs of negatively stained specimens. Hydration of axoplasmic fibres produced reversible changes in the X-ray pattern intensities, although the layer-line positions were unaltered. On the 4 nm layer-line, the intensity of the J3 reflection was dramatically reduced on hydration, though its position was unchanged. Hydration also affected the J10/J16 reflections, which increased in intensity, though here again the positions of the peaks were little altered. The X-ray patterns from our hydrated fibres resemble those produced by others from fibres of purified microtubules, though in our patterns contrast is generated towards the centre of the wall. We interpret our findings in the light of current ideas about microtubule structure as determined by X-ray diffraction and electron microscope techniques.

Animals↗
PubMed1989

Glycera dibranchiata hemoglobin. Structure and refinement at 1.5 A resolution.

The coelomic cells of the common marine bloodworm Glycera dibranchiata contain several hemoglobin monomers and polydisperse polymers. We present the refined structure of one of the Glycera monomers at 1.5 A resolution. The molecular model for protein and ordered solvent for the deoxy form of the Glycera monomer has been refined to a crystallographic R-factor of 12.7% against an X-ray diffraction dataset at 1.5 A resolution. The positions of 1095 protein atoms have been determined with a maximum root-mean-square (r.m.s.) error of 0.13 A, and the r.m.s. deviation from ideal bond lengths is 0.015 A and from ideal bond angles is 1.0 degree. The r.m.s. deviation of planar groups from their least-squares planes is 0.007 A, and the r.m.s. deviation for torsion angles is 1.2 degrees for peptide groups and 16.8 degrees for side-chains. A total of 153 water molecules has been located, and they have been refined to a final average occupancy of 0.80. Multiple conformations have been found for five side-chains, and a change has been suggested for the sequence at five residues. The heme group is present in the "reverse" orientation that differs only in the positions of the vinyl beta-carbons from the "normal" orientation. The doming of the heme towards the proximal side, and the bond distances and angles of the heme and proximal histidine are typical of most deoxy globin structures. The substitution of leucine for the distal histidine residue (E7) creates an unusually hydrophobic heme pocket.

Amino Acid Sequence↗
PubMed1991

Hierarchy of globin complexes. The quaternary structure of the extracellular chlorocruorin of Eudistylia vancouverii.

The molecular dimensions of the extracellular, hexagonal bilayer chlorocruorin of the polychaete Eudistylia vancouverii, determined by scanning transmission electron microscopy (STEM) of negatively stained specimens, were diameter of 27.5 nm and height of 18.5 nm. STEM mass measurements of unstained, freeze-dried specimens provided a molecular mass (Mm) of 3480 +/- 225 kDa. The chlorocruorin had no carbohydrate and its iron content was 0.251 +/- 0.021 wt%, corresponding to a minimum Mm of 22.4 kDa. Mass spectra and nuclear magnetic resonance spectra of the prosthetic group confirmed it to be protoheme IX with a formyl group at position 3. SDS/polyacrylamide gel electrophoresis, reversed-phase chromatography and N-terminal sequencing suggested that the chlorocruorin consists of at least three chains of approximately 30 kDa and five chains of approximately 16 kDa; the two types of subunits occur in the ratio 0.26:0.74(+/- 0.08). Complete dissociation of the chlorocruorin at neutral pH in the presence of urea or guanidine hydrochloride, followed by gel filtration, produced elution profiles consisting of three peaks, B, C and D. Fractions B and C consisted of the approximately 16 kDa chains and fraction D consisted of the approximately 30 kDa subunits. Mass measurements of particles in STEM images of unstained, freeze-dried fractions B and C provided Mm of 208 +/- 23 kDa and 65 +/- 12 kDa, respectively, in agreement with 191 +/- 13 kDa and 67 +/- 5 kDa obtained by gel filtration. Particles with Mm = 221 +/- 21 kDa were also observed in STEM images of unstained, freeze-dried chlorocruorin. These results imply that the chlorocruorin structure, in addition to the approximately 30 kDa linker subunits that have 0.26 to 0.47 heme groups/chain, comprises approximately 65 kDa tetramers and approximately 200 kDa dodecamers (trimers of tetramers) of globin chains. The stoichiometry of the tetramer and linker subunits calculated from molar amino acid compositions was 34 +/- 4 and 43 +/- 9. The complete dissociation of the chlorocruorin was accompanied by a 50 to 75% loss of the 55 +/- 14 Ca2+/mol protein, and was decreased to approximately 35% by the presence of 10 to 25 mM-Ca2+. Reassociation of dissociated chlorocruorin was maximal in the presence of 2.5 to 5 mM-Ca2+. The dodecamer and/or tetramer subunits in the absence or presence of Ca2+ exhibited very limited (less than 10%) reassociation into hexagonal bilayer structures, only in the presence of the linker subunit.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1977

Temperature-induced variations of blood acid-base status in the lugworm, Arenicola marina (L.): I. In vitro study.

Blood of the lugworm Arenicola marina studied in vitro behaved like a Rosenthal system: when temperature rose, pH decreased and PCO2 increased, whereas [HCO3] remained practically constant. pH values were low whatever the CCO2 and SO2. The temperature coefficient dpH/dt was always significantly different from the mean temperature-induced variations of the neutral pH of pure water between 0 and 30 degrees C. Consequently, the relative alkalinity of the blood, [OH-]/[H+], was very low (range, 1.53-5.06) and increased appreciably with temperature. Calculated changes in the fractional dissociation of protein imidazole groups, alphaIm, were smaller. The very variable buffer power of Arenicola hemoglobin was maximum (beta max) for a strictly defined, temperature-dependent value of pH (pH beta max), suggesting that as yet unidentified ionizable group on the hemoglobin molecule, RH, could be responsible for the pH-dependent changes of blood buffer power in Arenicola. Assuming pK'RH = PH beta max, the calculated fractional dissociation of RH, alpha RH, was constant between 0 and 30 degrees C. The nature of RH is discussed in relation with Reeves's hypothesis concerning the preeminence of protein imidazole groups in the regulation of extra- and intracellular pH.

Acid-Base Equilibrium↗
PubMed1977

Temperature-induced variations of blood acid-base status in the lugworm, Arenicola marina (L.): II. In vivo study.

Lugworms, Arenicola marina (L.), acclimatized at 16-17 degrees C, were acclimated at temperatures between 5.3 and 25.7 degrees C for 96 h. Whereas in vitro Arenicola blood behaves like a Rosenthal system, in vivo prebranchial blood does not: the higher the acclimation temperature, the lower the pHv and [HCO3]V, PVCO2, remaining practically constant. Nevertheless, the very low relative alkalinity of the blood in vivo ([OH-]/[H+] is less than 3), and the degree of dissociation of extra- and intracellular proteins, remain practically constant whatever the temperature. From examples in the literature together with these results, it is concluded that poikilothermic air-breathers and poikilothermic water-breathers regulate their blood pH in the face of temperature changes by contrasting mechanisms. In the first, regulation is almost instantaneous and takes place at the pulmonary level through adjustment of CO2 exchanges. In the second this regulation is slow and mainly extraventilatory, occurring through ionic exchanges. This contrast must be considered in relation with differences in blood PCO2 values, caused by the much higher O2 capacitance of air compared to water.

Acclimatization↗
PubMedDate not supplied

Oxygenation properties of the two co-occurring hemoglobins of the tube worm Riftia pachyptila.

Riftia pachyptila vascular blood and coelomic fluid contain two hemoglobin molecules that differ in their distribution and physical properties. The present study of the two isolated hemoglobins shows that both have an extremely high affinity for oxygen, but differ in their oxygenation characteristics. FI, the larger molecular weight (Mr) fraction (1,700,000), has a lower oxygen affinity, a well defined pH Bohr effect, and high cooperativity of oxygen binding. FII, the lower Mr fraction (400,000) has a higher oxygen affinity, no pH Bohr effect, and reduced cooperativity of oxygen binding. Both hemoglobins show marked effects of temperature on oxygen binding, and no effect of heme concentration or the presence of sulfide on oxygen affinity. The differences in the oxygenation properties and distribution of the two hemoglobins in the body fluids of Riftia pachyptila may allow them to play different roles in oxygen transport and storage for the animal which lives in the variable environment of the hydrothermal vents.

Animals↗
PubMed1994

Sex pheromones in marine polychaetes: steroids from ripe Nereis succinea.

A number of neutral marine steroids such as desmosterol, campesterol, brassicasterol, gorgosterol, and other trace steroids were isolated from the coelomic fluid of ripe Nereis succinea and checked for biological activity as sex pheromones on swarming specimens of Platynereis dumerilii and Nereis succinea. No significant influence of synthetic gorgosterol or a natural extract of gorgosterol or the other identified steroids on the swarming behavior was observed.

Animals↗
PubMed1980

Cuticle and mucous glands in the oesophagus of an annelid (Nereis virens).

The oesophagus of Nereis virens is divided into anterior and posterior regions and possesses several peculiar features not previously described for cuticle or glands of Polychaetes either in body or foregut integument. The mucous cells which are permanent glands in both regions secrete a carboxylated acidic mucus and possess apical mechanisms permitting the opening and closing of the neck of the glands. The cuticle of the posterior oesophagus bears numerous striated spines and several hypotheses concerning their physiological role are discussed.

Animals↗
PubMed1981

Evidence for a cerebral cholinergic system and suggested pharmacological patterns of neural organization in the prostomium of the polychaete Nereis virens (SARS).

The histological visualization of choline acetyltransferase (CAT) and acetylcholinesterase (AChE) on frozen sections of prostomia of Nereis virens indicate a concentration of cholinergic activity in the anterior brain. Components are probably sensory epithelial cells with cholinergic axons entering the brain in cephalic nerves and efferent cholinergic axons to prostomial muscle leaving the brain in the same nerves. There are also subepidermal cholinergic cells that may be second order motor neurons serving epidermal mucous cells. The smaller, second lobe of the corpora pedunculata and its associated vertical fibre tract are CAT(+) and appear continuous, on each side of the cerebral ganglion, with a dorsal and ventral longitudinal bundle of AChE(+) fibers. This system tapers to nothing at the level of the posterior eyes. There is a small AChE(+) component to each optic nerve and AChE is present in the nuchal epithelium. These observations are discussed in relation to earlier studies on aminergic and neurosecretory activity in the same ganglion.

Acetylcholinesterase↗