Calcium, Sulfhydryls and the Mitotic Apparatus

The in vivo mitotic apparatus (MA) of clam, worm and sea urchineggs may be augmented or dispersed by application of specificantimitotic agents. Glycols, which are antimitotic at concentrationsof 1–3% in sea water, cause a rapid massive increase inMA volume and retardation as seen in the polarizing microscope.Caffeine and dinitrophenol (DNP) cause a rapid disappearanceof the MA by shrinkage. Glycol effects can be balanced by DNPor caffeine if the agents are applied at the proper time andconcentration although normal cleavage does not ensue. Analysisof DNP and caffeine shrinkage suggests that they act indirectlyby causing release of calcium from intracellular stores, calciumcausing inactivation of polymerizable tubulin. DNP could causerelease of calcium either from mitochondria (if egg mitochondriahave a calcium uptake system) or by causing a decrease in ATPlevels which would inactivate calcium uptake systems such asthe Petzelt Ca⁺² ATP-ase or Kinoshita Ca⁺² uptake vesicles. Caffeine, while an inhibitor of the phosphodiesterase for cyclicAMP does not cause inhibition of the MA through the cyclic nucleotide.It is found that caffeine (and other methyl xanthines) causean inhibition of glutathione reductase activity in treated eggs.It is postulated that the calcium ATP-ases in the egg may becontrolled by reversible oxidation and reduction of their sulfhydrylsthus regulating calcium concentration in the cytosol. The possiblemodes of action of this system are discussed.     

A NEW SEMIONOTIFORM (ACTINOPTERYGII, NEOPTERYGII) FROM UPPER JURASSIC – LOWER CRETACEOUS DEPOSITS OF NORTH-EAST THAILAND, WITH COMMENTS ON THE RELATIONSHIPS OF SEMIONOTIFORMS

Abstract:  A new semionotiform fish, Isanichthys palustris gen. et sp. nov., is described from the Late Jurassic – Early Cretaceous Phu Kradung Formation, north-east Thailand. I. palustris is known from a single, nearly complete specimen found alongside abundant Lepidotes specimens at the Phu Nam Jun locality. I. palustris shows a mixture of semionotid-like characters, such as the pattern of cheek ossifications, and lepisosteid-like characters, such as the body shape and a dorsal fin opposed by an anal fin. I. palustris possesses only some of the characters currently used to define the Semionotidae. Cladistic analyses including various semionotid and gar taxa, together with Amia calva and Leptolepis coryphaenoides , suggest that the Semionotiformes (Lepisosteidae and 'Semionotidae') form a monophyletic clade, but the 'Semionotidae' taxa form an unresolved polytomy. The relationships between Semionotiformes, Halecomorphi and Teleostei are unresolved. When restricted to the best-known taxa, however, the analysis shows the monophyly of the Semionotidae sensu stricto ( Semionotus + Lepidotes ) and a sister-group relationship between halecomorphs and teleosts. These last two results are regarded as the preferred hypothesis for further studies. I. palustris is the only known example of a predaceous, probably piscivorous, 'semionotid'. It illustrates the great diversity and ecological adaptation of the semionotiforms during the Late Jurassic – Early Cretaceous. We question the phylogenetic relationships of 'ancient fishes' founded on molecular-based trees because we suspect that the use of very few Recent taxa as representatives of previously diverse lineages is an inevitable, but important, bias in the construction of such trees.     

Plasticity of Cadherin–Catenin Expression in the Melanocyte Lineage

Cadherins are calcium‐dependent cell adhesion receptors with strong morphoregulatory functions. To mediate functional adhesion, cadherins must interact with actin cytoskeleton. Catenins are cytoplasmic proteins that mediate the interactions between cadherins and the cytoskeleton. In addition to their role in cell–cell adhesion, catenins also participate in signaling pathways that regulate cell growth and differentiation. Cadherins and catenins appear to be involved in melanocyte development and transformation. Here, we investigated the function of cadherin–catenin complexes in the normal development and transformation of melanocytes by studying the patterns of expression of the cell–cell adhesion molecules, E‐, N‐ and P‐cadherin, and the expression of their cytoplasmic partners, α‐, β‐ and Γ‐catenin, during murine development. Similar analyses were performed in vitro using murine melanoblast, melanocyte, and melanoma cell lines in the presence and absence of keratinocytes, the cells with which melanocytes interact in vivo. Overall, the results suggest that the expression of cadherins and catenins is very plastic and depends on their environment as well as the transformation status of the cells. This plasticity is important in fundamental cellular mechanisms associated with normal and pathological ontogenesis, as well as with tumorigenesis.     

Photosynthetic and anatomical responses of Eucalyptus grandis leaves to potassium and sodium supply in a field experiment

Although vast areas in tropical regions have weathered soils with low potassium (K) levels, little is known about the effects of K supply on the photosynthetic physiology of trees. This study assessed the effects of K and sodium (Na) supply on the diffusional and biochemical limitations to photosynthesis in Eucalyptus grandis leaves. A field experiment comparing treatments receiving K (+K) or Na (+Na) with a control treatment (C) was set up in a K‐deficient soil. The net CO₂ assimilation rates were twice as high in +K and 1.6 times higher in +Na than in the C as a result of lower stomatal and mesophyll resistance to CO₂ diffusion and higher photosynthetic capacity. The starch content was higher and soluble sugar was lower in +K than in C and +Na, suggesting that K starvation disturbed carbon storage and transport. The specific leaf area, leaf thickness, parenchyma thickness, stomatal size and intercellular air spaces increased in +K and +Na compared to C. Nitrogen and chlorophyll concentrations were also higher in +K and +Na than in C. These results suggest a strong relationship between the K and Na supply to E. grandis trees and the functional and structural limitations to CO₂ assimilation rates.     

Serologic Characteristics of Glucokinases from Entamoeba histolytica and Related Species1

SYNOPSIS. An enzyme inhibition technic was employed for quantitative comparison of the serologic properties of glucokinases from 4 groups of amebas which are structurally indistinguishable species: Entamoeba histolytica, E. moshkovskii, E. invadens and E. terrapinae. Antiglucokinase was prepared by immunizing rabbits with crude extracts of DKB and Laredo strains of E. histolytica. The combination of amebal glucokinase and homologous antibody was a pseudoirreversible reaction. The inhibition was proportional to the amount of antibody until at least 60% of the enzyme was inhibited, and the inhibition was 96–92% in the region of antibody excess. The nature of the inhibition was uncompetitive with respect to substrate. The presence of substrate had no effect upon the inhibition. Anti-DKB glucokinase inhibited equally glucokinases from DKB, JH, K9, 200, NRS, BH, JI, F22, and N strains. Anti-Laredo glucokinase equally inhibited glucokinases from Laredo, Huff, JA, AG, and 403 strains; 2.5–2.9 times as much antiserum was required to produce the same degree of inhibition between antisera and strains of heterologous group as with homologous antigen. Anti-DKB and anti-Laredo glucokinases cross-reacted with the enzyme from E. moshkovskii, but not with enzymes from reptilian amebas. A new glucokinase-anti-glucokinase dissociation test was developed which provides a method for qualitative differentiation of antiglucokinase against DKB strain from anti-glucokinase against Laredo strain.     

Osteology and relationships of Thaiichthys nov. gen.: a Ginglymodi from the Late Jurassic – Early Cretaceous of Thailand

Abstract: The osteology of Thaiichthys buddhabutrensis, nov. gen., from the Late Jurassic – Early Cretaceous of Thailand is described on the basis of a collection of well‐preserved specimens. The mode of preservation of the material allows describing the external anatomy, as well as some elements of the internal anatomy (braincase, elements of the vertebral column). Most of the cranial and postcranial skeleton shows a rather conservative anatomy for ‘semionotiformes’, but the jaw apparatus displays specializations. Variations observed in the ossification pattern of the skull roof and of the cheek, in the morphology of the median dorsal scales and in fin rays’ count indicate that caution should be applied when these characters are used in diagnoses and in phylogenetic analyses. A phylogenetic analysis including a set of gars, of ‘semionotiformes’, of Macrosemiiformes and of Halecomorphi shows the following features: (1) the monophyly of Holostei; (2) sister‐pair relationships between Tlayuamichin/Semiolepis, Isanichthys/’Lepidotes’ latifrons and Araripelepidotes/Pliodetes; (3) the latter pair, together with Thaiichthys and possibly ‘Lepidotes’ mantelli, are resolved as stem Lepisosteiformes; and (4) the ‘semionotiformes’ (a group gathering species of Semionotus and Lepidotes) do not form a clade.     

An ammonite–fish association from the Kimmeridgian (Upper Jurassic) of La Rochelle, western France

A partially disarticulated actinopterygian fish preserved in a large three-dimensional ammonite body chamber is described from the Kimmeridgian of western France. Taphonomic observations on the degree of preservation of the fish and the development of epibiont organisms on the inner wall of the shell indicate a rather long time interval before sediment totally filled the body chamber. The fish, referred to an indeterminate Macrosemiidae, probably used this empty ammonite ( Rasenioides , Aulacostephanidae) shell as a refuge, or possibly for spawning and/or brooding. It can be assumed that ammonite shells may have constituted common shelters for demersal fishes living in an open-marine shelf environment, near to a muddy bottom devoid of rocks.