Observations on the fine structure of the cercaria of Notocotylus attenuatus and formation of the cyst wall of the metacercaria

Summary The dorsal tegument of the mature cercaria of Notocotylus attenuatus is a syncytial, cytoplasmic layer, containing two types of secretory granule which are identifiable ultrastructurally. The type 1 secretory bodies are electron lucid, whereas most type 2 granules have a banded appearance. The ventral tegument contains granules which are secreted from the type 3 cells; the type 3 granules are membrane bound, electron dense, and consist of both an amorphous and a finely striated zone. The type 4 cells mainly contain cigar-shaped granules consisting of an amorphous core surrounded by concentric striations. The granules exhibit structural variability in shape and content. The type 4 cells undergo a cellular migration to the tegument during encystment. The structure of the posterior-lateral glands and mode of secretion of the granules are described. Possible functions of microtubules are discussed for each cell type. Details of some secretory processes involved in the formation of the hemispherical cyst wall are described. The layers of the cyst wall may be related to the granular contents of the various parenchymal cells of the cercaria. The tegument of the metacercaria originates primarily from the cytoplasm of the type 1, type 2, type 3 and type 4 cells.     

Solution conformations of proline rings in proteins studied by NMR spectroscopy

Summary Three different conformations of proline rings in a protein in solution, Up, Down and Twist, have been distinguished, and stereospecific assignments of the pyrrolidine -, - and -hydrogens have been made on the basis of ¹H-¹H vicinal coupling constant patterns and intraresidue NOEs. For all three conformations, interhydrogen distances in the pairs -³, ³-³, ²-², ²-², and ³-³ (2.3 Å) are shorter than those in the pairs -², ²-³, ³-², ²-³, and ³-² (2.7–3.0 Å), resulting in stronger NOESY cross peaks. For the Up conformation, the ³-² and ²-³ spin-spin coupling constants are small (<3 Hz), and weak cross peaks are obtained in a short-mixing-time (10 ms) TOCSY spectrum; all other vicinal coupling constants are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. For the Down form, the -², ²-³, and ³-² vicinal coupling constants are small, leading to weak TOCSY cross peaks; all other couplings again are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. In the case of a Twist conformation, dynamically averaged coupling constants are anticipated. The procedure has been applied to bovine pancreatic trypsin inhibitor and Cucurbita maxima trypsin inhibitor-V, and ring conformations of all prolines in the two proteins have been determined.     

Characterization of human chromosomal unit fibers

A structural component of mitotic chromosomes that partially explains the compaction of DNA within mitotic chromosomes is suggested on the basis of the occurrence of long, regular cylindrical structures in preparations of isolated human chromosomes. These structures, unit fibers, of a rather constant diameter of about 4,000 Å have been postulated to be formed by coiling of the 250T2–300 Å solenoid chromatin fiber that itself is formed by coiling of the 100 Å string of nucleosome fiber. The human chromatid would thus be composed by a hierarchy of helices with contraction ratios for DNA at each level of coiling of 7 (string of nucleosomes), 5 (solenoid) and 40 (4,000 Å unit fiber or super-solenoid) which results in an overall contraction ratio for DNA in the unit fiber structures of about 1,400, which is approximately 5-fold less than the final contraction of DNA in intact chromatids of condensed metaphase chromosomes. The present report concerns more detailed studies with respect to the dimensions and cytochemical properties of the unit fiber structures observed in preparations of isolated human mitotic chromosomes that provide direct and indirect evidence in support of their super-solenoid structure and relate to known properties of human mitotic chromosomes.     

Meiotic studies ofElymus nutans andE. jacquemontii (Poaceae,Triticeae) and their hybrids withPseudoroegneria spicata and seventeenElymus species

Hybridizations ofElymus nutans andE. jacquemontii were carried out with one species ofPseudoroegneria (S genome), and 20Elymus species, each containing either of the SH, SY, SYH, or SYW genomes. Chromosome configurations were analysed at metaphase I of the two target taxa and their interspecific hybrids. It is concluded that (i)E. nutans is an allohexaploid containing the SYH genomes, andE. jacquemontii is an allotetraploid having the SY genomes; (ii) the genomic affinity is associated with the geographic distance between the species studied; (iii) minor genomic structural rearrangements have occurred within the hexaploid taxon ofE. nutans.     

Polygonal inequalities as a key to neuronic equations

Neuronic or decision equations, first proposed as a mathematical model of neural activity, have shown, after their exact, compact solution was found, typical behaviours that make them natural tools for General Systems studies. It is shown here that their mathematical investigation is remarkably furthered by generalizing the triangular inequality to polygonal ones. These permit the immediate computation of the tensorial expansion of linearly separable boolean functions, and exhibit clearly the connection between their continuous and discontinuous aspects.     

Infloreszenz- und Blütenentwicklung bei der KugeldistelEchinops exaltatus (Asteraceae)

InEchinops the flowers are surrounded by several scales and initiated in an acropetal and spiral succession on a cone-like inflorescence axis (Figs. 1–6). The floral organs originate in the following sequence: petals—stamens—carpels—pappus. The petals arise from a meristematic rim and therefore are already interconnected when they arise as primordia. This sympetalous zone remains rather inconspicuous for a long period, but eventually, the elongated corolla tube is formed through intercalary growth in a ring zone. Thereby, the stamens are moved upwards and form ledges on the corolla tube (Fig. 34). In the inferior ovary the usual zones of the typical angiospermous gynoecium can be distinguished, namely a synascidiate, symplicate and hemisymplicate zone. The ovule is borne on carpellary tissue.

     

Monoparticulate glycogen in human liver

Summary Round granules about 200 Å in diameter have been observed in the sinusoids bordering cells of human liver and possibly also in the hepatocytes. These granules clustered together to form clumps 0.3 in diameter, are enclosed in a fine cytoplasmic membrane, and are very similar in appearance to the so-called monoparticulate glycogen present in cells of extrahepatic tissues. These granules are of glycogenic nature as shown by their sensitivity to a prolonged diastase treatment.Assistent of the Institute of Medical Pathology, University of Padova.     

Molecular mapping of a new gene Rrs4 CI 11549 for resistance to barley scald (Rhynchosporium secalis)

Doubled haploid (DH) progeny from a cross between the scald susceptible barley (Hordeum vulgare L.) cultivar Ingrid and the resistant accession CI 11549 (Nigrinudum) was evaluated for resistance in the pathogen Rhynchosporium secalis (Oudem) J.J. Davis. Two linked and incompletely dominant loci confer resistance CI 11549 against isolate 4004. One is an allele at the complex Rrs1 locus on chromosome 3H close to the centromere; the other is located 22 cM distally on the long arm. The latter locus is designated Rrs4. In BC₃-lines into Ingrid from CI 2222 (another Nigrinudum) resistance seems governed by one locus close to the telomeric region of chromosome 7H, probably allelic to Rrs2. In neither case did we find any trace of the recessive gene rh8 reported to be present in Nigrinudum. Various resistance donors of Ethiopian origin designated as Nigrinudum, Jet or Abyssinian were identical to a great extent with respect to markers, but differed in resistance to different isolates of scald or in barley yellow dwarf virus (BYDV) resistance. The implications for their use as differentials in scald tests and screening of germplasm collections are discussed.     

Cell multiplication and ultrastructure ofMicrasterias denticulata (Desmidiaceae) grown under salt stress

Cells ofMicrasterias denticulata Bréb. were kept in nutrient solution of high osmolality (salt stress) for four weeks. In a special cell multiplication test it was established that cell division is gradually inhibited at increasing salt concentrations and totally arrested at the highest concentration (26 mosm/kg). Recovery studies proved that even cells from the highest concentration range start dividing immediately after being placed in aqua bidest. thus indicating the full reversibility of the inhibiting effect. — Cells of the highest concentration range show marked ultrastructural changes. Besides an enormous accumulation of starch and oil bodies and a condensed appearance of the ground plasma, a reduction of mitochondria, ER and the Golgi-system is found. The most striking effect occurs on the vacuolar system which appears extremely reduced and condensed. The cell wall is thickened by the formation of an additional cell wall layer with a spongy electron microscopical appearance. Through the cell wall many droplets of a probably fat-like substance are excreted. — In summary, salt stress induces growth-inhibited akinete cells in the sense ofFritsch; these can be reactivated by decreasing the salt concentration. The salt-induced akinete state seems to be an ecological adaption to unfavourable conditions rather than a degeneration of the cells.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday.23. 12. 1988     

Purification and characterization of aspartate aminotransferase from developing embryos of the camel tick Hyalomma dromedarii

Aspartate transaminase (AST) activity in the camel tick Hyalomma dromedarii was followed throughout embryogenesis. During purification of AST to homogeneity, ion exchange chromatography lead to four separate forms (termed I, II, III and IV). AST II with the highest specific activity was pure after chromatography on Sephacryl S-300. The molecular mass of AST II was 52KDa for the native enzyme, composed of one subunit of 50KDa. AST II had a Km value of 0.67mM for -ketoglutarate and 15.1mM for aspartate. AST II had a pH optimum of 7.5 with heat stability up to 50°C for 15min. The enzyme was activated by MnCl₂, and inhibited by CaCl₂, MgCl₂, NiCl₂, and ZnCl₂.     

Moral commitment without objectivity or illusion: Comments on Ruse and Woolcock

Peter Woolcock, in Ruse's Darwinian Meta-Ethics: A Critique, argues that the subjectivist (nonobjectivist) Darwinian metaethics proposed by Michael Ruse (in Taking Darwin Seriously) cannot work, because the illusion of objectivity that Ruse claims is essential to morality breaks down when it is recognized as illusion, and there then remain no good reasons for acknowledging or following moral obligations. Woolcock, however, is mistaken in supposing that moral behaviour requires rational motivation. Ruse's Darwinian metaethical analysis shows why such objective support for morality is neither plausible nor necessary; and when that is recognized, it can also be seen that Ruse's proposed illusion of moral objectivity is superfluous.     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

β-D-Glycan synthases and the CesA gene family: lessons to be learned from the mixed-linkage (1→3),(1→4)β-D-glucan synthase

Cellulose synthase genes (CesAs) encode a broad range of processive glycosyltransferases that synthesize (14)-D-glycosyl units. The proteins predicted to be encoded by these genes contain up to eight membrane-spanning domains and four `U-motifs' with conserved aspartate residues and a QxxRW motif that are essential for substrate binding and catalysis. In higher plants, the domain structure includes two plant-specific regions, one that is relatively conserved and a second, so-called `hypervariable region' (HVR). Analysis of the phylogenetic relationships among members of the CesA multi-gene families from two grass species,Oryza sativa and Zea mays, with Arabidopsis thaliana and other dicotyledonous species reveals that the CesA genes cluster into several distinct sub-classes. Whereas some sub-classes are populated by CesAs from all species, two sub-classes are populated solely by CesAs from grass species. The sub-class identity is primarily defined by the HVR, and the sequence in this region does not vary substantially among members of the same sub-class. Hence, we suggest that the region is more aptly termed a `class-specific region' (CSR). Several motifs containing cysteine, basic, acidic and aromatic residues indicate that the CSR may function in substrate binding specificity and catalysis. Similar motifs are conserved in bacterial cellulose synthases, the Dictyostelium discoideum cellulose synthase, and other processive glycosyltransferases involved in the synthesis of non-cellulosic polymers with (14)-linked backbones, including chitin, heparan, and hyaluronan. These analyses re-open the question whether all the CesA genes encode cellulose synthases or whether some of the sub-class members may encode other non-cellulosic (14)-glycan synthases in plants. For example, the mixed-linkage (13)(14)-D-glucan synthase is found specifically in grasses and possesses many features more similar to those of cellulose synthase than to those of other -linked cross-linking glycans. In this respect, the enzymatic properties of the mixed-linkage -glucan synthases not only provide special insight into the mechanisms of (14)-glycan synthesis but may also uncover the genes that encode the synthases themselves.     

Glucosylation of cyclodextrin-complexed podophyllotoxin by cell cultures of Linum flavum L.

The glucosylation of the cytotoxic lignan podophyllotoxin by cell cultures derived from Linum flavum was investigated. Four cyclodextrins: -cyclodextrin, -cyclodextrin, dimethyl--cyclodextrin and hydroxypropyl--cyclodextrin were used to improve the solubility of podophyllotoxin by complexation. Dimethyl--cyclodextrin met our needs the best and the solubility of podophyllotoxin could be enhanced from 0.15 to 1.92 mM, using a podophyllotoxin/cyclodextrin ratio of 1:1. Growth parameters of the cell suspensions were not affected neither by the addition of cyclodextrins alone, nor when complexed podophyllotoxin was dissolved in the medium.The complexed lignan disappeared rapidly from the culture medium, within 24h, under all experimental conditions. Almost simultaneously, between 73 and 100% of detectable podophyllotoxin was bioconverted into podophyllotoxin--d-glucoside. A maximal bioconversion rate of 0.51 mmol l^-1 suspension day^-1 was calculated for the L. flavum cells growing in a medium which included the podophyllotoxin/dimethyl--cyclodextrin complex at a final concentration of 1.35 mM.     

Über die Verwendung der reversibel polymeren Metachromasie von Pseudoisocyanin zur Gewebsfärbung

Zusammenfassung 1. Pseudoisocyanin gibt mit den dicht gelagerten elektronegativen Gruppen von Mukopolysacchariden in Geweben und Lösungen, wie auch mit synthetischen Produkten mit linear angeordneten elektronegativen Gruppen in Lösung wie z. B. Polyäthylensulfosäuren eine metachromatische Reaktion mit der charakteristischen langwelligen Bande (vgl.Scheibe u.Schauer 1958). Die elektronegativen Gruppen binden die Farbstoffmoleküle elektrostatisch und bilden die Gruppierung des reversiblen Polymerisates.2. Die metachromatische Reaktion mit der reversibel polymeren Bande läßt sich in Gewebsschnitten deutlich demonstrieren. Das Farbstoffpolymerisat absorbiert in Lösung bei der gleichen Wellenlänge wie im Gewebe, wodurch die Gleichheit der Vorgänge im Gewebe und in Lösung bewiesen ist.3. Das Pseudoisocyanin erscheint für die Darstellung von Mukopolysacchariden besonders geeignet, da nach früheren Arbeiten (Scheibe 1938,Zimmermann u.Scheibe 1956) schon eine monomolekulare Schicht die reversibel polymere Bande und damit die Metachromasie beobachtbar macht. Ferner sind bei Betrachtung der mit Pseudoisocyanin gefärbten Schnitte im monochromatischen Licht bei der Wellenlänge der polymeren Absorption Spuren von Mukopolysacchariden noch deutlich zu erkennen, die bei Betrachtung im weißen Licht unauffällig bleiben.4. An Hand einiger Beispiele (Mastzellen, Knorpelgewebe, hyalinisiertes Bindegewebe) wird die Verwendungsmöglichkeit in der Histochemie gezeigt.

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Summary 1. Pseudoisocyanin interacts with densly positioned electronegative groups of mucopolysaccharides in tissues and in solutions in the same way as it interacts with linear positioned electronegative groups of synthetic products in solution (for instance polyaethylensulfoacids). The metachromasia, which is due to this reaction of pseudoisocyanin with mucopolysaccharides shows a characteristic wave-band 5727 Å (Scheibe undSchauer 1958). The dye is bound electrostatically by the electronegative groups in form of a reversible polymerisate.2. The metachromatic reaction with the reversible polymerisate has been demonstrated in tissue-sections. The polymerisate with the dyestuff is shown to adsorb light at the same wavelength in tissues as in solutions. This finding confirms the identity of the reaction in tissues and in solutions.3. Pseudoisocyanin seems to be especially suited for the detection of mucopolysaccharides, for even a monomolecular layer of dyestuff allows the observation of the reversible polymeric band and therefore shows metachromasia. Further, after staining with pseudoisocyanin even small trans of mucopolysac charides which are not visible in the white light can be demonstrated by means of monochromatic light at the wave-length of the polymer absorption.4. As shown by staining mastcells, cartilage-tissue, hyaliniced connectivetissue, pseudoisocyanin seems to be of use for appliance in histochemistry.

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The chromosomal locations and linkage relationships of the structural genes for the prolamin storage proteins (secalins) of rye

Summary Rye secalins are a polymorphic mixture of polypeptides which are classified into four major groups. Previous studies have shown that the structural genes for two of the groups (the -secalins and 40K -secalins) are located on the short arm of chromosome 1R and those for a third group (the high molecular weight secalins) on the long arm of the same chromosome. Analysis of F₂ grain from crosses between inbred lines of S. cereale shows that the structural genes for the -secalins (designated Sec 1) and the high molecular weight secalins (designated Sec 3) are loosely linked (40.8 ±3.76% recombination, 57.4 ± 11.30 cM). Analysis of wheat rye addition lines shows that the structural genes for the 75K -secalins are present on chromosome 2R. This locus is provisionally designated Sec 2. These genes are probably derived from those for the 40K -secalins by duplication, divergence and translocation. Analysis of secalin fractions from wild species of rye shows that all contain 75K -secalins, indicating that the duplication and divergence, if not the translocation, occurred before speciation of the genus.     

Vectorial and Octupolar Components of the First-Order Hyperpolarizability in Push-Pull Benzopyranic Series

Vectorial (weight 1) and octupolar (weight 3) components of the first-order hyperpolarizability are computed using the PM3/RHF/FF method following two different decomposition schemes. These calculations evidence the importance of the weight 3 component of the tensor even in push-pull molecules. The values, output from the two decomposition schemes, are different but show the same evolutionary trend within benzopyranic molecule series. The square root of a macroscopic square average quantity ,²)^1/2 (which is usually determined in elastic second-harmonic light scattering experiment) is then computed and compared to the norm of the molecular cartesian tensor.     

Synaptische Strukturen und Elementargranula in der Neurohypophyse des Meerschweinchens

Zusammenfassung Die Ultrastruktur des Nucleus infundibularis tuberis, der Zona interna, der Zona externa und des Hypophysenhinterlappens von Meerschweinchen wird beschrieben. Vergleichende Beobachtungen an den Nervenfasern der genannten Gebiete zeitigen folgende Ergebnisse:Die Axone der Zona interna und des Hypophysenhinterlappens enthalten gleichgeartete, große neurosekretorische Elementargranula (1,400 Å). Die Axonquerschnitte im Bereich des Nucleus infundibularis tuberis und der Zona externa weisen Granula gleichen Kalibers (800 Å) auf und lassen damit auf einen funktionell-morphologischen Zusammenhang des Nucleus infundiburis und der Zona externa schließen. Ob die kleinen Elementargranula das morphologische Substrat der sogenannten releasing factors darstellen oder ob es sich um adrenerge Axone und Endigungen mit typischen Katecholamingranula handelt, ist nicht zu klären.Es wird unterschieden zwischen echten Synapsen und synapsenähnlichen Kontakten. Nur erstere zeigen alle klassischen Synapsenmerkmale. Ihnen sind im Bereich der Neurohypophyse axosomatische und interaxonale Synapsen zuzuordnen. Zona externa und Hypophysenhinterlappen stellen neurohämale Kontaktzonen dar und zeichnen sich durch gleichartig konstruierte Synapsen aus. Neben interaxonalen Synapsen treten vor allem neurokapilläre Kontakte in den Vordergrund. In der Zona externa sind die Tanyzyten synaptisch mit Axonen verknüpft, so wie im Hypophysenhinterlappen die Pituizyten synaptische Verbindungen mit Nervenfasern eingehen. Die synapsenähnlichen Bildungen im Verlauf und an den Enden der Axone können somit neurokapillärer, neurotanyzytärer und neuropituizytärer Natur sein. Sie enthalten neben den synaptischen Vesikeln auch meist kleine oder große Elementargranula. Die ähnliche Morphologie der synaptischen Bildungen in der Zona externa und im Hinterlappen läßt einen gleichgearteten Inkretionsmechanismus beider neurohypophysärer Abschnitte vermuten. Tanyzyten und Pituizyten könnten dabei eine Überträgerfunktion ausüben. Eine rezeptorische Funktion der Tanyzyten wird gleichfalls diskutiert.Die Drüsenzellen der Pars intermedia der Hypophyse sind durch direkte neuroglanduläre Kontakte mit den Neuronen des Hypothalamus verknüpft. Die Axone stülpen sich hierbei tief in das Zytoplasma der Drüsenzellen ein. Es entstehen dadurch beim Meerschweinchen drei nervöse Endigungsformen, die Synapsen ausbilden: 1. Endigungen, die nur synaptische Vesikel enthalten; 2. Endigungen mit synaptischen Vesikeln und kleinen Granula; 3. Endigungen mit synaptischen Vesikeln und großen Granula.Zwischen den Drüsenzellen der Pars infundibularis der Adenohypophyse sind ebenfalls Axonquerschnitte zu beobachten. Es handelt sich dabei entweder um vegetative Faserbündel oder Nervenfasern mit kleinen Granula wie in der Zona externa (800 Å).

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Summary The ultrastructure of the nucleus infundibularis tuberis, the inner and outer layer of the median eminence and the posterior lobe of the guinea pig are described. Comparative studies on the nerve fibres of these regions lead to the following conclusions:The axons of the inner layer of the median eminence and of the posterior lobe contain similar types of large, neurosecretory elementary granules (Diameter 1400 Å).The cross-sections of the axons in the area of the nucleus infundibularis tuberis and of the outer layer of the median eminence exhibit the same sized granules (Diameter 800 Å), which points to a functional-morphological relationship between the two. Whether the small elementary granules represent the morphological substrate of the so-called releasing factors, or whether it is a question of adrenergic axons and terminations with typical catecholamine granules, is undecided.A distinction is made between true synapses and synapse-like contacts. Only the former display all the classical characteristics of synapses. To this sort must be classed the axosomatic and interaxonal synapses in the neurohypophysis. The external layer of the median eminence and the posterior lobe are distinguished by neurohaemal contact areas and show similarly constructed synapses. Of particular prominence, besides interaxonal synapses, are neurocapillary contiguities. Just as in the posterior lobe the pituicytes show synaptic connections with nerve fibres, so are the tanycytes in the outer layer of the median eminence in synaptical contact with axons. Thus the synapse-like formations along and at the endings of the axons can be of a neurocapillary, neurotanycytial and neuropituicytial nature. They contain, apart from the synaptic vesicles, mainly small but also large elementary granules. The similar morphology of the synaptic formations in the outer layer of the median eminence and the posterior lobe suggests the existence of a similar mechanism of internal secretion in both these neurohypophysial areas. Tanycytes and pituicytes could exercise a carrier function. A possible receptor-function of the tanycytes is considered.The glandular cells of the pars intermedia of the hypophysis are linked by means of direct neuroglandular contacts with the neurons of the hypothalamus, whereby the axons make deep incursions into the cytoplasm of the glandular cells. In the guinea pig three types of termination can be observed that form synapses: 1. terminations that contain only synaptic vesicles; 2. terminations with small granules; 3. terminations with large granules.Cross-sections of axons can also be observed between the glandular cells of the pars infundibularis of the adenohypophysis. Here they can be identified either as vegetative fibre-bundles or as nerve fibres with small granules, such as occur in the outer layer of the median eminence (Diameter 800 Å).

     

Involvement of Erks activation in cadmium‐induced AP‐1 transactivation in vitro and in vivo

Cadmium is a potent and effective carcinogen in rodents and has recently been accepted by IARC (International Agency for Research on Cancer) as a category 1 carcinogen. Cadmium-induced upregulation of intracellular signaling pathways leading to increased mitogenesis is thought to be a major mechanism for the carcinogenic activity following chronic cadmium exposure. In the present study, we found that exposure of cells to cadmium induced significant activation of AP1 and all three members of the MAP kinase family in mouse epidermal JB6 cells. The induction of AP1 activity by cadmium appears to involve activation of Erks, since the induction of AP1 activity by cadmium was blocked by pretreatment of cells with PD98058. Interestingly, the induction of AP1 by cadmium was greatly enhanced by the chemical tumor promoter, TPA and the growth factor EGF, but not by ultraviolet C radiation. In vivo studies demonstrated that cadmium could also induce transactivation of AP1 in AP1luciferase report transgenic mice. Considering the role of AP1 activation in tumor promotion, the results presented in this study provide a possible molecular mechanism for cadmiuminduced carcinogenesis.     

A model for the pattern of deposition of microfibrils in the cell wall of Glaucocystis

Freeze-fracturing of Glaucocystis nostochinearum Itzigsohn cells during cell-wall microfibril deposition indicates that unidirectionally polarized microfibril ends are localized in a zone of synthesis covering about 30% of the sarface area of the plasma membrane. Within this zone there are about 6 microfibril ends/m² cell surface. It is proposed that microfibrils are generated by the passage of their tips over the cell surface and that the pattern of microfibril organization at the poles of the cells, in which microfibrils of alternate layers are interconnected at 3 rotation centres, results directly from the pattern of this translation of microfibril tips. In a model of the deposition pattern it is proposed that the zone of synthesis may split into 3 sub-zones as the poles are approached, each sub-zone being responsible for the generation of one rotation centre. It is demonstrated that the microfibrillar component of the entire wall could be generated by the steady translation of the microfibril tips (at which synthesis is presumed to occur) over the cell surface at a rate of 0.25–0.5 m min^-1. Microcinematography indicates that the protoplast rotates during cell-wall deposition, and it is proposed that this rotation may play a role in the generation of the microfibril deposition pattern.