Evolution of glutamate dehydrogenase genes: Evidence for two paralogous protein families and unusual branching patterns of the archaebacteria in the universal tree of life

Summary The existence of two families of genes coding for hexameric glutamate dehydrogenases has been deduced from the alignment of 21 primary sequences and the determination of the percentages of similarity between each pair of proteins. Each family could also be characterized by specific motifs. One family (Family 1) was composed of gdh genes from six eubacteria and six lower eukaryotes (the primitive protozoan Giardia lamblia, the green alga Chlorella sorokiniana, and several fungi and yeasts). The other one (Family 11) was composed of gdh genes from two eubacteria, two archaebacteria, and five higher eukaryotes (vertebrates). Reconstruction of phylogenetic trees using several parsimony and distance methods confirmed the existence of these two families. Therefore, these results reinforced our previously proposed hypothesis that two close but already different gdh genes were present in the last common ancestor to the three Ur-kingdoms (eubacteria, archaebacteria, and eukaryotes). The branching order of the different species of Family I was found to be the same whatever the method of tree reconstruction although it varied slightly according the region analyzed. Similarly, the topological positions of eubacteria and eukaryotes of Family II were independent of the method used. However, the branching of the two archaebacteria in Family II appeared to be unexpected: (1) the thermoacidophilic Sulfolobus solfataricus was found clustered with the two eubacteria of this family both in parsimony and distance trees, a situation not predicted by either one of the contradictory trees recently proposed; and (2) the branching of the halophilic Halobacterium salinarium varied according to the method of tree construction: it was closer to the eubacteria in the maximum parsimony tree and to eukaryotesin distance trees. Therefore, whatever the actual position of the halophilic species, archaebacteria did not appear to be monophyletic in these gdh gene trees. This result questions the firmness of the presently accepted interpretation of previous protein trees which were supposed to root unambiguously the universal tree of life and place the archaebacteria in this tree. Offprint requests to: B. Labedan     

Ecology of Soil Erosion in Ecosystems

Each year, about 75 billion tons of soil are eroded from the world's terrestrial ecosystems. Most agricultural land in the world is losing soil at rates ranging from 13 tons/ha/year to 40 tons/ha/year. Because soil is formed very slowly, this means that soil is being lost 13–40 times faster than the rate of renewal and sustainability. Rain and wind energy are the two prime causes of erosion from tilled or bare land. Erosion occurs when the soil lacks protective vegetative cover. Soil erosion reduces the productivity of the land by loss of water, soil organic matter, nutrients, biota, and depth of soil. The greatest threat to providing food for a rapidly growing human population is soil erosion. Abandoned, eroded agricultural land is replaced by clearing forested ecosystems. Received 17 February 1998; accepted 26 May 1998.     

Postnatal Evolution of the γ-Aminobutyric Acid/Benzodiazepine Receptor Complex in a Model of Inherited Epilepsy: The Quaking Mouse

Binding assays of [3H]muscimol and [3H]-flunitrazepam have been performed on brain homogenates of brainstem, cerebellum, and forebrain of genetically epileptic quaking (qk) mutant mice 20, 40, 70, and 90 days old and their corresponding controls of the same strain (C57BL/6J). The endogenous gamma-aminobutyric acid (GABA) content has been determined in various brain regions of 70-day-old qk and control mice. Finally, the behavioral effects of diazepam, of the mixed GABAA/GABAB receptor agonist progabide, and of the selective GABAB receptor agonist baclofen have been assessed in adult qk mutants. Our results strongly suggest a lack of involvement of GABAergic neurotransmission in the inherited epilepsy of the qk mutant mouse.     

The consequences of egg cannibalism inAdalia bipunctata [Coleoptera: Coccinellidae]

When eggs ofAdalia bipunctata L. are offered to larvae of their own species, these larvae are able to develop to adults. Reducing the daily egg supply results in decreased larval survival and pupal weight and especially fecundity of the adult females. The duration of larval development is significantly increased, the longevity of adults is shortened.     

Do we have a right to an unmanipulated genome? The human genome as the common heritage of mankind

The human genome is commonly regarded as a ‘natural’ connection between all human beings, as it has been handed down to us by our predecessors. As such, it is believed to represent common heritage of humanity, e.g. a resource of outstanding value that should be the object of special protection and international concern. Some critics argue that germline manipulation would disrupt this natural heritage and that we have a duty to preserve the integrity of the human germline. However, a closer look reveals that the concept of common heritage of humanity does not necessarily imply the impermissibility of germline manipulation. If it is restricted to the prevention of severe diseases, germline manipulation does not represent a threat to the unity and identity of the human species, even though this would create a new form of relationship between human beings, namely that between a designer and a genetically designed person.