Membranous tubes in pseudoscorpion spermiogenesis

The highly complicated differentiation of the spermatid in the pseudoscorpion Diplotemnus sp. is accomplished without the presence of microtubules. Instead membranous tubes measuring approximately 50 nm in diameter and closely associated with endoplasmic reticulum are found from early to mid spermatids. The lumen of the tube is devoid of electron dense contents but a fluffy material is attached to the cytoplasmic side. They run straight or slightly bent and are in open connection with the cell membrane. First appearing near the cell bridge of the interconnected spermatids they form a bundle in the longitudinal axis during a transitory phase of elongation. When the cell rounds off again the tubules together with the endoplasmic reticulum disappear. The arrangement of the tubes and their presence during abortive elongation of the spermatid suggest a supportive function commonly attributed to microtubules. Moreover, the open connection with the cell membrane and their close association with the endoplasmic reticulum may indicate their participation also in transport.     

Neuromedin U-immunoreactivity in the nervous system of the small intestine of the pig and its coexistence with substance P and CGRP

Summary In the small intestine of the pig, neuromedin U (NMU)-immunoreactivity was mainly confined to the nerve plexus of the inner submucosal and mucosal regions. After colchicine treatment, a high number of immunoreactive nerve cell bodies was observed in the plexus submucosus internus (Meissner), whereas only a low number was found in the plexus submucosus externus (Schabadasch). The plexus myentericus as well as the aganglionic nerve meshworks in the circular and longitudinal smooth muscle layers almost completely lacked NMU-immunoreactivity. Double-labeling experiments demonstrated the occurrence of distinct NMU-containing neuron populations in the plexus submucosus internus: (1) relatively large type-II neurons revealing immunoreactivity for NMU and calcitonin gene-related peptide (CGRP) and/or substance P (SP); (2) a group of small NMU- and SP-immunoreactive neurons; (3) a relatively low number of small neurons displaying immunoreactivity for NMU but not for SP. Based on its distributional pattern, it is concluded that NMU plays an important role in the regulation and control of mucosal functions.     

Nontoxic and toxic oligopeptides with D-amino acids and unusual residues in Microcystis aeruginosa PCC 7806

Toxic and nontoxic peptides were isolated from the cyanobacterium Microcystis aeruginosa PCC 7806 by a procedure including extraction of cells with water-saturated 1-butanol, chromatography of the extract on silica gel plates and high performance liquid chromatography (HPLC) on Partisil-5. The toxin was shown to be only a minor constituent, being negatively charged and thus separable by electrophoresis, within the HPLC-purified fraction. It contained erythro-β-methyl-D-Asp, D-Glu, D-Ala, L-Leu, and L-Arg known to be part of the Microcystis peptide-toxin with M_r 994. The major part of the HPLC-purified fraction was assigned, however, to a nontoxic peptide with a M_r of 956. Partial hydrolysis studies of the nontoxic peptide(s) revealed amino acid sequences composed of D-Glu, N-methyl-Phe, and 3,4-dehydro-Pro, aside from the common L-amino acids. Cyclic linkage in the nontoxic peptide(s) appears likely.     

Protein kinase C inhibition by calmodulin and its fragments

Inhibition of protein kinase C (PKC) by calmodulin is investigated and we describe the localization of inhibitory sequences within the calmodulin molecule. We present evidence that calmodulin inhibits PKC through an inhibition of the activation of PKC associated with lipid membranes: Binding of PKC to lipid vesicles is not affected, but activation is abolished. The potent calmodulin antagonist R24571 (calmidazol) did not affect the inhibition of PKC by calmodulin at concentrations up to 10^–5 M. Two tryptic fragments of calmodulin were isolated which inhibited PKC. They were only slightly less potent than intact calmodulin with an IC₅₀ of 6 µ M compared to 1 µ M of intact calmodulin. They were identified as Ser³⁸-Arg⁷⁴ and His¹⁰⁷-Lys¹⁴⁸. Each of the inhibiting fragments contains an intact Ca²⁺-binding domain with complete helix-loop-helix structure (EF hand). Other calmodulin peptides showed only weak inhibitory activity. Both fragments did not stimulate cAMP phosphodiesterase even at concentrations 100-fold higher than the calmodulin concentration needed for maximal stimulation. None of the fragments acted as a calmodulin antagonist.     

Ectopic head and foot formation in Hydra: Diacylglycerol-induced increase in positional value and assistance of the head in foot formation

In wild type Hydra magnipapillata, daily application of the protein kinase C activator diacylglycerol (DAG) evokes sprouting of periodically spaced ectopic heads along the body column and leads to loss of the ability to regenerate proximal structures including the foot. The present transplantation studies show that the appearance of ectopic heads is preceded by an early increase in the 'positional value' (P-value) or 'head activation potential' of the gastric column. Long before ectopic head structures emerge, pieces of DAG-treated tissue transplanted into the corresponding positional level of untreated hosts induce head formation instead of being integrated, whereas pieces implanted from untreated donors into DAG-treated hosts form feet. Foot formation implies a decrease in the P-value. This down-regulation is promoted through long-range assistance by the head. Thus, after termination of the DAG treatment ectopic feet are intercalated midway between the periodically spaced heads; moreover, untreated polyps onto which additional distal heads have been grafted regenerate feet faster than do one-headed polyps and may form supernumerary feet. Multiheaded animals can also be produced using two substances (K-252a and xanthate D609) that interfere with signal transduction, but the mode by which secondary heads arise is different from DAG-induced ectopic head formation. Presumably because the assistance by the parental head is impaired, buds fail to form a foot and detach and instead give rise to stable secondary body axes. It is assumed that the P-value along the body varies according to the number of cellular receptors for factors serving as intercellular signals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Core substructure in Mastigocladus laminosus phycobilisomes

A native high molecular complex (M_r 850000) containing about 50% of the allphycocyanin of the phycobilisome but lacking allophycocyanin B was separated from isolated phycobilisomes by gel electrophoresis. It was designated AP_CM since the large linker polypeptide L_CM was exclusively localized in this complex. The complex exhibited a ?196°C fluorescence emission maximum at 673 nm (671 nm at 25°C). In addition, a core complex (designated AP_C, M_r≥1000000) consisting of both AP_CM and AP 680 was isolated by combined gel filtration and linear gradient centrifugation. At 25°C this complex showed dual emission peaks at 670 and 680 nm demonstrating functional independence of the terminal emitters. A complex similar to AP_CM can be isolated from phycobilisomes of Anabaena variabilis. This is evidence that AP_CM is the constitutive center of the tricylindrical core of hemidiscoidal cyanobacterial phycobilisomes. Two models summarizing the structural and functional consequences of the results are presented in the discussion.     

Isolation of a crotoxin-like protein from the venom of a South American rattlesnake (Crotalus durissus collilineatus)

1. A crotoxin-like protein was isolated from the venom of a South American rattlesnake Crotalus durissus collilineatus. 2. Many of its properties are similar to those of crotoxin, including its non-covalent heterodimeric structure, electrophoretic mobility on SDS-PAGE, isoelectric focusing properties, toxicity in mice, immunological reactivity, multiple isoforms, phospholipase activity, peptide map, and instability on an anion-exchange column. 3. Results indicate that "collilineatus toxin" is strongly homologous with crotoxin, found in the venom of Crotalus durissus terrificus, and all other characterized rattlesnake neurotoxins.     

Aminopyridazine derivatives and TXA2-PGI2 balance

Experiments carried out under the conditions adopted showed the strong affinity of aminopyridazine derivatives for the eicosanoids TXA2 and PGI2. But this affinity depended on the chemical structure of the molecule: a small change in the radical grafted onto the pyridazine ring could completely modify the pharmacological activity of the molecule. Consequently it should be possible to control the properties of pyridazine derivatives according to pharmacological needs. Thus: --pyridazin-3-one derivatives were mainly active on TXA2 biosynthesis: 2-aminoalkyl 5-arylidene 6-methyl (4H) pyridazin-3-ones inhibited the TXA2-synthesizing activity of cardiac tissue whereas 3-amino 4,6-diaryl pyridazin-3-ones were specific inhibitors of the TXA2 synthetase in vitro, but these effects were weak. --pyridazine derivatives were devoid of any effect on the TXA2-synthesizing activity of cardiac tissue: they acted on either TXA2 synthetase or PGI2 synthetase according to the radicals grafted onto the pyridazine ring. --none of the compounds under study was active on the PGI2-synthesizing activity of cardiac tissue.     

Comparative effects of some 3-amino 4,6-diarylpyridazines on the biosynthesis in vitro of TXA2 and PGI2- and on the TXA2- and PGI2-synthesizing activities of cardiac tissue

Some 3-amino 4,6-diarylpyridazine derivatives were tested for their effects on TXA2 and PGI2 biosyntheses in vitro and on the TXA2- and PGI2-synthesizing activities of cardiac tissue. Horse platelet and aorta microsomes were used as sources of thromboxane and prostacyclin synthetases respectively. The TXA2- and PGI2-synthesizing activities of cardiac tissue were studied on isolated perfused rabbit hearts (the heart microsomes being used both as TXA2 synthetase and PGI2 synthetase sources). TXB2 and 6-keto PGF1 alpha were determined by RIA. Among the compounds under study, 3-morpholino 4,6-diphenylpyridazine (III) was shown to inhibit specifically the TXA2 synthetase. Substitution of the morpholino group by a dimethylamino one (I) reinforced the inhibiting effects on TXA2 synthetase but it also revealed a slight anti-prostacyclin synthetase action of the molecule. Replacement of 3-morpholino moieties by either a 3-hydrazino (IV), or a 2-dimethylaminoethylamino (V), or a 2-morpholinoethylamino group (VI) abolished completely the effects of the molecule on TXA2 and PGI2 synthetases. Likewise the addition of chlorine on the para-position on the phenyl ring of I neutralized all its inhibitory effects both on TXA2 and PGI2 synthetases in vitro. None of the 3-amino 4,6-diarylpyridazine derivatives was active on either the TXA2- or PGI2-synthesizing activities of cardiac tissue.     

Pattern of cell proliferation in embryogenesis and planula development ofHydractinia echinata predicts the postmetamorphic body pattern

Summary During embryogenesis and planula development of the colonial hydroidHydractinia echinata cell proliferation decreases in a distinct spatio-temporal pattern. Arrest in S-phase activity appears first in cells localized at the posterior and then subsequently at the anterior pole of the elongating embryo. These areas do not resume S-phase activity, even during the metamorphosis of the planula larva into the primary polyp. Tissue containing the quiescent cells gives rise to the terminal structures of the polyp. The posterior area of the larva becomes the hypostome and tentacles, while the anterior part of the larva develops into the basal plate and stolon tips. In mature planulae only a very few cells continue to proliferate. These cells are found in the middle part of the larva. Labelling experiments indicate that the prospective material of the postmetamorphic tentacles and stolon tips originates from cells which have exited from the cell cycle in embryogenesis or early in planula development. Precursor cells of the nematocytes which appear in the tentacles of the polyp following metamorphosis appear to have ceased cycling before the 38th hour of embryonic development. The vast majority of the cells that constitute the stolon tips of the primary polyp leave the cell cycle not later than 58 h after the beginning of development. We also report the identification of a cell type which differentiates in the polyp without passing through a post-metamorphic S-phase. The cell type appears to be neural in origin, based upon the identification of a neuropeptide of the FMRFamide type.