Grafting the molecular phylogenetic tree with morphological branches to reconstruct the evolutionary history of the genus Zaprionus (Diptera: Drosophilidae).

A molecular phylogeny for the drosophilid genus Zaprionus was inferred using a mitochondrial (CO-II) and a nuclear (Amyrel) gene using 22 available species. The combined molecular tree does not support the current classification, dubbed phylogenetic, based entirely upon a morphocline of forefemoral ornamentation. For species for which DNA was not available, phylogenetic positioning was only assigned using morphological characters. In order to avoid conflict between DNA and morphology in the combined analyses (supermatrix method), we developed a new method in which few morphological characters were sampled according to an a priori homoplasy assessment on the consensus molecular tree. At each internal node of the tree, a number of synapomorphies was determined, and species with no molecular sequences were grafted thereon. Analogously to tree vocabulary, we called our method 'morphological grafting'. New species groups and complexes were then defined in the light of our findings. Further, divergence times were estimated under a relaxed molecular clock, and historical biogeography was reconstructed under a maximum likelihood model. Zaprionus appears to be of recent origin in the Oriental region during the Late Miocene ( approximately 10 MYA), and colonization of Africa started shortly after ( approximately 7 MYA) via the maritime route of the Indian Ocean Islands. Most of the morphological and ecological diversification took place, later, in Western Africa during the Quaternary cyclic climatic changes. Furthermore, some species became recent invaders, with one, Zaprionus indianus, has successfully invaded South and North America during the last decade.

Amplification of the 1731 LTR retrotransposon in Drosophila melanogaster cultured cells: origin of neocopies and impact on the genome.

Transposable elements (TEs), represent a large fraction of the eukaryotic genome. In Drosophila melanogaster, about 20% of the genome corresponds to such middle repetitive DNA dispersed sequences. A fraction of TEs is composed of elements showing a retrovirus-like structure, the LTR-retrotransposons, the first TEs to be described in the Drosophila genome. Interestingly, in D. melanogaster embryonic immortal cell culture genomes the copy number of these LTR-retrotransposons was revealed to be higher than the copy number in the Drosophila genome, presumably as the result of transposition of some copies to new genomic locations [Potter, S.S., Brorein Jr., W.J., Dunsmuir, P., Rubin, G.M., 1979. Transposition of elements of the 412, copia and 297 dispersed repeated gene families in Drosophila. Cell 17, 415-427; Junakovic, N., Di Franco, C., Best-Belpomme, M., Echalier, G., 1988. On the transposition of copia-like nomadic elements in cultured Drosophila cells. Chromosoma 97, 212-218]. This suggests that so many transpositions modified the genome organisation and consequently the expression of targeted genes. To understand what has directed the transposition of TEs in Drosophila cell culture genomes, a search to identify the newly transposed copies was undertaken using 1731, a LTR-retrotransposon. A comparison between 1731 full-length elements found in the fly sequenced genome (y(1); cn(1)bw(1), sp(1) stock) and 1731 full-length elements amplified by PCR in the two cell line was done. The resulting data provide evidence that all 1731 neocopies were derived from a single copy slightly active in the Drosophila genome and subsequently strongly activated in cultured cells; and that this active copy is related to a newly evolved genomic variant (Kalmykova, A.I., et al., 2004. Selective expansion of the newly evolved genomic variants of retrotransposon 1731 in the Drosophila genomes. Mol. Biol. Evol. 21, 2281-2289). Moreover, neocopies are shown to be inserted in different sets of genes in the two cell lines suggesting they might be involved in the biological and physiological differences observed between Kc and S2 cell lines.

A nested alpha-amylase gene in Drosophila ananassae.

The amylase gene family of Drosophila ananassae consists in seven copies, scattered on several chromosomal arms. We have evidenced that a member of the family, Amy35, lies within an intron of a gene homologous to the CG14696 gene of D. melanogaster. This nested arrangement seems restricted to the D. ananassae subgroup. The nested and the nest genes are encoded on opposite strands. Both are actively transcribed in the midgut at the same time, raising the possibility of interference between their mRNAs. Our data also help to elucidate the history of the Amy family, suggesting that Amy35 arose by duplication and translocation from another ancestral locus, into a formerly short intron, in an ancestor of the subgroup.

[Effects of two inhibitors of RNA synthesis (Actinomycin D and α-amanitin) on embryonic development of an insect: Gene activity from the beginning of embryogenesis inLeptinotarsa decemlineata]. / Comparaison des effets de deux inhibiteurs de la synthèse d'ARN (Actinomycine D et α-amanitine) sur le développement embryonnaire d'un insecte: déterminisme génique du début de l'embryogénèse deLeptinotarsa decemlineata (Coleoptera).

Actinomycin D and α-amanitin were injected into the embryos ofLeptinotarsa from intravitelline cleavage stages to gastrula stages. The effect of injection was controlled. Following the treatment, embryogenesis was blocked at different stages: blastula (pseudo-blastula), abnormal gastrula and atypical germ band. The stages reached depend on the age of treatment. Treatment of intravitelline cleavage stages strongly inhibits morphogenesis: embryos are blocked mainly at the blastula stage (79 to 97%). Treatment of blastoderm formation stages shows different features: gastrulation is at first prevented in 80% of cases, but the capacity to gastrulate is acquired rapidly during the first blastodermic cell cycle; embryos treated at late blastoderm stages reach the germ band stage.From these results, two periods have been characterized in the early embryogenesis ofLeptinotarsa: 1. the intravitelline cleavage period is unaffected by the inhibitor of RNA synthesis. All information needed for cleavage and early blastoderm formation is already present in the fertilized egg, probably in the form of materialmRNA. 2. The blastoderm formation period is involved in further morphogenesis. New information, for the development of late blastula, gastrula and germ band is produced during succesive blastoderm cell cycles. The actinomycin D and α-amanitin treatments show that the acquisition of new morphogenetic capacities is contemporaneous with the arrival of nuclei in the periplasm.