Gene conversion in avian mesotocin and vasotocin genes: A recurrent mechanism linking two neurohypophysial precursor lineages?

Amino acid sequences of the first half of MSEL- and VLDV-neurophysins from goose and chicken have been determined. Identical substitutions in positions 17, 18, 35, 36 and 41 of both neurophysins of a given species when compared with their mammalian counterparts suggest a gene conversion between vasotocin—MSEL-neurophysin and mesotocin—VLDV-neurophysin genes. This event, which has already been observed for three mammalian species, seems recurrent and would link the evolution of the two neurohypophysial hormone precursors.     

Kinetics of pleuridial growth in Antithamnion plumula (Rhodophyceae)

The filamentous and branched thallus of Antithamnion plumula is constitued of two different kinds of branches with apical growth: the cladomial axes with a continuous or indefinite growth, and the pleuridia with a limited growth. The size of the pleuridia depends on their position with respect to the lateral cladomial axes.The growth kinetics of 35 pleuridia were analysed using Nelder's generalized logistics. Each sigmoidal curve, which was divided into four growth stages from the instantaneous acceleration variations, was thus characterized by ten kinetic parameters: lengths at the time of the changes in growth stage, durations of the growth stages and maximum growth rate.The data showed that all curves displayed a marked left dissymmetry which reflected the brevity of the accelerated growth stage (1/5 of total growth duration). The maximum acceleration stage occurs between the individualization of the pleuridial initial cell and the first mitosis. Previously known experimental data were related to this quantitative result so as to put forward a biological meaning. New research pathways were suggested.The kinetic parameters investigated were used for a classification of pleuridia. The smallest ones displayed the slowest growth: they needed twice more time to reach their maximum size than the largest pleuridia whose growth was the fastest. This association of traits was related to the occurrence of acropetal fluxes along the main axis of the thallus.     

A new translocation in Burkitt's tumor cells

Summary A t(8;22)(q24;q11) translocation was found in blood, bone marrow, and ascites cells from a European Burkitt's lymphoma. Cell surface markers were identified as monoclonal IgG. The relationship between these two unusual findings is questionable in this cytologically typical Burkitt's lymphoma.     

The influence of the environment (natural and experimental) on the composition of the exine of allergenic pollen with respect to the deposition of pollutant mineral particles

Pollen material of the two anemophilous plants of known allergic significance Dactylis glomerata (Poaceae) and Betula verrucosa (Betulaceae) was collected at several places (in Sweden and France) and exposed to natural or experimental conditions. This material was analyzed with Electron Probe X Microanalysis (EPMA) (System ORTEC 5000) attached to a Scanning Electron Microscope (Jeol JMS 35), or with EDAX, a 10000 X-Ray Analyser, Link System, connected to a SEM-microscope (Jeol JSM 820).

It is clear that the environment has an effect on such a co-inductor or adjuvant of allergenicity as K. The possible presence of pollutant inorganic (mineral) particles on the pollen grain surface may play a role in the allergenic activity. Pollen, consequently, may be used as sensitive biological indicators of atmospheric pollution.     

Le phenomene d'heteroblastie chez les vegetaux: Comment l'expliquer?

Heteroblastic development is often observed in Cormophytae, but it can also be characterized in Thallophytae as shown by the detailed investigation of the development of the algaAntithamnion plumula (Ceramiaceae, Rhodophyta). In this species, heteroblasty concerns (i) dimensional variables (such as pleuridia length and lateral cladome first tagma length) and (ii) variables that characterize the cell growth kinetics (main axis cells). Apex curvature also varies during ontogenesis.The generality of the property in plants led to search for its origin: apical meristem own dynamics, ontogenetic evolution of internal relationships, dialectical relationships between the plant and its environment.Some models were put forward to accout for the development ofAntithamnion but did not take into account the heteroblasty phenomenon. The investigations presented here are a first attempt at representation through formal grammar, based on double wall map systems. The model leads to the assumption of the occurrence of an oscillatory mechanism associated with a threshold that determines both qualitatively (axial cell of the cladomophoric or pleuridiophic type) and quantitatively the development of the whorls.