Implication of Cytoplasmic Factors in the Lethality of Bufonidae Nucleocytoplasmic Hybrids

The nucleocytoplasmic hybrid combination performed by nuclear graft between B. bufo nucleus and B. calamita egg is 95% lethal during gastrulation mostly at the young gastrula stage (75%) and to a lesser extent at the yolk plug stage (20%). The heterologous B. calamita cytoplasm was treated or fractioned by different techniques including centrifugation, nucleic acid extraction, ammonium sulfate treatment and heating.
The treated cytoplasmic fractions were injected in B. bufo fertilized eggs in order to check their influence on morphogenetic capacities of the B. bufo nucleus. Injection of hyaline cytoplasmic fraction obtained from B. calamita centrifuged eggs blocks the B. Bufo fertilized egg gastrulation in similar rates as in nucleocytoplasmic association performed by interspecific nuclear grafting. Gastrulation, however, is not affected by injection of total nucleic acids extracted from this hyaline fraction. The soluble cytoplasmic fraction obtained after 60% ammonium sulfate precipitation blocks the development at the beginning of gastrulation, this property being inactivated by heating for 5 min at 60°C. Supernatant from 70% ammonium sulfate precipitation blocks the development at the yolk plug stage and is inactivated by heating for 5 min at 80°C.
These experiments suggest that two distinct factors in B. calamita eggs are involved in developmental arrest of injected B. bufo fertilized eggs, these two factors respectively acting on the beginning and on the end of gastrulation.     

Occurrence of early post-hatching Jurassic Nautilida in Normandy, France: palaeobiologic, palaeoecologic and palaeobiogeographic implications

Nautilida are present and sometimes abundant in various sedimentary environments of the Jurassic series (Sinemurian to Kimmeridgian) in Normandy, but in the majority of cases the individuals are mature or at a late stage of ontogenetic development. Comparative analysis of the palaeobiogeographic distribution of Nautilida according to their ontogenetic stages shows that early post-hatching specimens are present only in particular palaeoenvironments which are rarely visible and laterally limited in outcrop. The sedimentologic and palaeoecologic originality of the Carixian, Aalenian and Bajocian deposits bearing these peculiar specimens is related to their palaeogeographic position along the western border of the Anglo-Paris Basin, on the eastern margin of the Armorican Massif, where Jurassic deposits overlie Palaeozoic rocky reefs or shoals. The egg-laying places of the Jurassic Nautilida show palaeoenvironmental features similar to those of the recent Nautilus, having been controlled by the water temperature and the nature and morphology of the sea bottoms. A hard, anfractuous and stable substratum, low sedimentation rates and warm and well-oxygenated marine waters appear to have been required for egg-laying and for the embryonic development of these cephalopods. The discovery of early post-hatching fossil Nautilida is fundamental to a better understanding of their palaeobiogeographic distribution at local to global scales. The stenotopic nature of their egg-laying places explains the segregation between newly hatched individuals and the rest of the population and leads also to a distinction between the notions of ‘dispersal potential’ and ‘settlement potential’ for populations of Nautilida. Three palaeobiogeographic maps show that Nautilida were absent in the Jurassic Boreal realm. This exclusion could be closely dependent on the thermal requirements that govern their reproduction. By comparison, the contemporary occurrence of ammonoids in this realm appears to reflect differences in reproductive strategies.     

Effects of lithium and potassium on recovery of solute uptake capacity of Acer pseudoplatanus cells after gas-shock

At concentrations of 10-^?3M, Li⁺ inhibits the recovery of solute uptake capacity of Acer pseudoplatanus L. cell suspension cultures after gas-shock (i.e. after rapid exchange of the atmosphere in the culture flasks for ambient air). It also reduces solute uptake capacity of cells having already attained high rates of uptake during recovery from gas-shock. The effects of Li⁺ are much greater in cells which have been cultivated in 7 mM K⁺ solution than in cells cultivated with higher K⁺ levels (19 mM). Increasing K⁺ concentration during recovery reverses the effect of 10^–3M Li⁺ and, with sufficiently high concentrations of K⁺ (≥ 10-^?2M) during recovery, the solute uptake capacity of the fully recovered cells can even become greater than that of the control, at least for the low values of substrate concentration (here sulphate 10-^?5M). Since Li⁺ does not affect the time course of solute uptake measured over 15–20 min, it is thought that it interacts with the synthesis and turnover of the solute uptake machinery of the Acer pseudoplatanus cells. Thermodynamic analysis of the flux data also supports the hypothesis that Li⁺ inhibits the biosynthesis of specific sites of solute permeation, but it does not rule out the possibility that K⁺ interferes rather on the forces acting on the transport of the considered solutes than on the catalytic structures of permeation.     

Cytoplasmic Influence on Lethality in Nucleocytoplasmic and Natural Hybrids between Bufo Calamita Laur and Bufo Bufo L. (Amphibia, Anura)

Nucleocytoplasmic interactions have been studied through nuclear and cytoplasmic grafts. Bufo bufo nuclei transplanted in Bufo calamita eggs provoked 95% lethality during gastrulation. Influence of the cytoplasm in such a nucleocytoplasmic incompatibility has been studied through cytoplasmic fractionation and grafting of the fractions obtained. Fractionation of egg cytoplasm gave three fundamental fractions: lipid, hyaline cytoplasm and vitellus. After injection of B. calamita fractions into B. bufo fertilized eggs, the hyaline cytoplasmic fraction provoked a gastrulation block in the same ratio (95%) as in the interspecific nuclear graft experiment. Influence of the hyaline cytoplasmic fractions of both species has been tested on nucleocytoplasmic and natural hybrid developments. The B. calamita hyaline cytoplasmic fraction provoked in each case a developmental block at the beginning of gastrulation. The B. bufo hyaline cytoplasmic fraction acts later at the yolk plug stage and in some cases partially corrects the developmental bolck or exogastrulation of young hybrid gastrula. It can be generalized that in both kinds of hybrids, the hyaline cytoplasmic fraction of B. calamita exerted a lethal effect on B. bufo nucleus.     

Adenosine Inhibition of Human Platelet Aggregation by ADP

WE have shown that in human platelet-rich plasma, inosine is a concentration-dependent inhibitor of adenosine incorporation into platelets^1,2 and at high concentrations inosine inhibits adenosine decomposition³. This prompted us to investigate the effect of inosine and other adenosine decomposition products on aggregation of human platelets in vivo by ADP.     

Evidence for Hybridization by Multilocus Enzyme Electrophoresis and Random Amplified Polymorphic DNA Between Leishmania braziliensis and Leishmania panamensis/guyanensis in Ecuador

ABSTRACT. The taxonomic attribution of four Leishmania stocks isolated from humans in Ecuador has been explored by both multilocus enzyme electrophoresis and random amplified polymorphic DNA. For three loci, MLEE results showed patterns suggesting a heterozygous state for a diploid organism, while the corresponding homozygous states are characteristic of the Leishmania panamensis/guyanensis complex and Leishmania braziliensis . RAPD profiles exhibited for several primers a combination of the Leishmania panmensis/guyanensis complex and L. braziliensis characters. These data hence suggest that the four stocks are the results of hybridization between L. panamensis/guyanensis and L. braziliensis . MLEE data show that the results cannot be attributed to either mixture of stocks, or an F1 in the framework of a simple Mendelian inheritance.     

Increased Inactivation of Messengers in <Emphasis Type="Italic">Escherichia coli ts</Emphasis> Mutant

WE recently described some of the properties of a temperature sensitive mutant of Escherichia coli (refs. 1–3 and unpublished work) in which RNAase II activity is increased on transfer to the non-permissive temperature^1,2, while the functional half-life of β-galactosidase mRNA¹ and the chemical half-life of the lac Operon mRNA³ are decreased. Questions raised by these studies were (a) can the strain be considered a general messenger RNAase mutant and (b) what is the direction of messenger inactivation in this strain? The latter question is particularly interesting since the increased RNAase activity in this strain is that of RNAase II (unpublished work) which degrades RNA molecules in the 3′ to 5′ direction⁴, while mRNA is known to be degraded in the 5′ to 3′ direction^5,6.     

A new polypterid fish: Polypterus faraou sp. nov. (Cladistia, Polypteridae) from the Late Miocene, Toros-Menalla, Chad

Polypterus faraou sp. nov. (Cladistia, Polypteridae) from the Late Miocene of Toros-Menalla (western Djourab, Chad) is described on the basis of a subcomplete articulated skeleton preserved in three dimensions. This is the first time such a complete fossil polypterid skeleton has been described. It is the only verifiable fossil record for the genus Polypterus . P. faraou closely resembles P. bichir and P. endlicheri , extant fish found in the Chad–Chari system. Intrarelationships among the polypterids are not yet resolved: however, P. faraou shows a primitive shape of the body and a primitive shape of the opening of the lateral line on the scales, similar to that of three living species ( P. bichir , P. endlicheri and P. ansorgii ).  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 227–237.