Search PubMed⌕ Search

Biomedical subjects

D Tautz

Publications and source records attributed to D Tautz.

At least 55 records · Page 3Linked to original sources
PubMed1998

Regulation of the Tribolium homologues of caudal and hunchback in Drosophila: evidence for maternal gradient systems in a short germ embryo.

In short germ embryos, the germ rudiment forms at the posterior ventral side of the egg, while the anterior-dorsal region becomes the extra-embryonic serosa. It is difficult to see how an anterior gradient like that of bicoid in Drosophila could in these embryos be directly involved in patterning of the germ rudiment. Moreover, since it has not yet been possible to recover a bicoid homologue from any species outside the diptera, it has been speculated that the anterior bicoid gradient could be a late addition during insect evolution. We addressed this question by analysing the regulation of potential target genes of bicoid in the short germ embryo of Tribolium castaneum. We demonstrate that homologues of caudal and hunchback from Tribolium are regulated by Drosophila bicoid. In Drosophila, maternal caudal RNA is translationally repressed by bicoid. We find that Tribolium caudal RNA is also translationally repressed by bicoid, when it is transferred into Drosophila embryos under a maternal promoter. This strongly suggests that a functional bicoid homologue must exist in Tribolium. The second target gene, hunchback, is transcriptionally activated by bicoid in Drosophila. Transfer of the regulatory region of Tribolium hunchback into Drosophila also results in regulation by early maternal factors, including bicoid, but in a pattern that is more reminiscent of Tribolium hunchback expression, namely in two early blastoderm domains. Using enhancer mapping constructs and footprinting, we show that caudal activates the posterior of these domains via a specific promoter. Our experiments suggest that a major event in the evolutionary transition from short to long germ embryogenesis was the switch from activation of the hunchback gap domain by caudal to direct activation by bicoid. This regulatory switch can explain how this domain shifted from a posterior location in short germ embryos to its anterior position in long germ insects, and it also suggest how an anterior gradient can pattern the germ rudiment in short germ embryos, i.e. by regulating the expression of caudal.

Animals↗
PubMed1997

A screen for fast evolving genes from Drosophila.

In an attempt to quantify the rates of protein sequence divergence in Drosophila, we have devised a screen to differentiate between slow and fast evolving genes. We find that over one-third of randomly drawn cDNAs from a Drosophila melanogaster library do not cross-hybridize with Drosophila virilis DNA, indicating that they evolve with a very high rate. To determine the evolutionary characteristics of such protein sequences, we sequenced their homologs from a more closely related species (Drosophila yakuba). The amino acid substitution rates among these cDNAs are among the fastest known and several are only about 2-fold lower than the corresponding values for silent substitutions. An analysis of within-species polymorphisms for one of these sequences reveals an exceptionally high number of polymorphic amino acid positions, indicating that the protein is not under strong negative selection. We conclude that the Drosophila genome harbors a substantial proportion of genes with a very high divergence rate.

Animals↗
PubMed1997

Paternity assessment and population subdivision in a natural population of the larger mouse-eared bat Myotis myotis.

A hypervariable simple sequence locus and mitochondrial D-loop sequences were used to analyse genetically a natural population of the larger mouse-eared bat Myotis myotis in southern Bavaria. Tests for population subdivision and direct observations suggest that females return to their natal sites, while males disperse. The males present in female nursery colonies are not related to the females. Paternity assessment for 46 offspring from a particular nursery colony showed that there are no males that monopolize the reproduction, and that the resident males in the colony had only a small mating success. Instead, the results suggest that females actively seek matings outside their colony. Most interestingly, it appears that a group of males about 16 km away from the nursery colony had a relatively high mating success and that this group of males may be related to the females of the nursery colonies. If this finding can be confirmed in a larger study, it may have important consequences for future conservation strategies.

Animals↗
PubMed1997

Polymorphism and locus-specific effects on polymorphism at microsatellite loci in natural Drosophila melanogaster populations.

We have studied the natural variation at microsatellite loci in two African and five non-African populations of Drosophila melanogaster. Ten dinucleotide simple sequence loci were cloned from chromosomally mapped P1 clones and typed for single individuals from isofemale lines of the respective populations. We find that the African populations harbor the largest degree of diversity, while the non-African populations show a lower diversity. This supports previous results that D. melanogaster originated in Africa and spread across the rest of the world in historic times. Using genetic distance measures, we find also a distinct population subdivision between the non-African populations. Most interestingly, we find for some loci in some populations a strongly reduced variability, which cannot be explained by bottleneck effects. Employing a conservative test based on the variance in repeat number, we find that at least one locus in one population deviates significantly from the expectations of mutation-drift equilibrium. We suggest that this may be due to a recent selective sweep in this chromosomal region that may have been caused by a linked locus that was involved in local adaptation of the population.

Adaptation, Physiological↗
PubMed1997

An episodic change of rDNA nucleotide substitution rate has occurred during the emergence of the insect order Diptera.

We have studied the potential reasons for a conspicuous deviation of substitution rates in Dipteran ribosomal genes. Systematic pairwise relative-rate tests reveal that a significant increase in substitution rate is characteristic for Diptera, but not for the other insects analyzed. Estimation of sequence change in specific lineages reveals that most of these substitutions took place during the evolution of the Dipteran stem lineage. When related to the paleontologically documented periods of absolute time, the substitution rate in the stem lineage of the Diptera underwent an at least 20-fold increase compared to other insect groups and subsequently dropped by a factor of 10 before the diversification of the major Dipteran subgroups. Systematic comparisons of nucleotide composition show that this episodic change in substitution rate was accompanied by a significant increase in A+T content of Dipteran rDNA. Our data suggest that the episodic evolution of the Dipteran rDNA has most probably been caused by a change of directional mutation pressure which must have occurred during the evolution of the stem lineage of the Diptera.

Animals↗
PubMed1997

Evolution and phylogeny of the Diptera: a molecular phylogenetic analysis using 28S rDNA sequences.

Portions of the large ribosomal subunit RNA gene (28S rDNA) encompassing the D1 and the D7 region were obtained from 16 dipteran species and families to reconstruct early phylogenetic events in the order Diptera. For outgroup comparison, the corresponding sequences were used from representative taxa of the Siphonaptera, Mecoptera, and Lepidoptera. A subset of 488 unambiguously alignable sites was analyzed with respect to important sequence evolution parameters. We found (1) sequence variability is significantly higher in double-stranded sites than in single-stranded sites, (2) transitions are close to saturation in most pairwise sequence comparisons, (3) significant substitution rate heterogeneity exists across sites, and (4) significant substitution rate heterogeneity exists among lineages. Tree reconstruction was carried out with the neighbor joining, maximum parsimony, and maximum likelihood methods. Four major subgroups are consistently and robustly supported: the Brachycera, the Culicomorpha, the Tipulomorpha sensu stricto, and the hitherto controversial Bibionomorpha sensu lato, which includes the families Sciaridae, Mycetophilidae, Cecidomyiidae, Bibionidae, Scatopsidae, and Anisopodidae. The phylogenetic relationships within or among these subclades and the positions of the families Psychodidae and Trichoceridae were not robustly resolved. These results support the view that the mouthparts of extant dipteran larvae evolved from a derived ground state characterized by subdivided and obliquely moving mandibles. Furthermore, sequence divergence and the paleontological record consistently indicate that a period of rapid cladogenesis gave rise to the major dipteran subgroups.

Animals↗
PubMed1996

Class 3 Hox genes in insects and the origin of zen.

We have cloned, from a beetle and a locust, genes that are homologous to the class 3 Hox genes of vertebrates. Outside the homeobox they share sequence motifs with the Drosophila zerknüllt (zen) and z2 genes, and like zen, are expressed only in extraembryonic membranes. We conclude that the zen genes of Drosophila derive from a Hox class 3 sequence that formed part of the common ancestral Hox cluster, but that in insects this (Hox) gene has lost its role in patterning the anterio-posterior axis of the embryo, and acquired a new function. In the lineage leading to Drosophila, the zen genes have diverged particularly rapidly.

Amino Acid Sequence↗
PubMed1995

Ribosomal DNA phylogeny of the major extant arthropod classes and the evolution of myriapods.

The evolutionary relationships among arthropods are of particular interest because the best-studied model system for ontogenetic pattern formation, the insect Drosophila, is a member of this phylum. Evolutionary inferences about the developmental mechanisms that have led to the various designs of the arthropod body plan depend on a knowledge of the phylogenetic framework of arthropod evolution. Based on morphological evidence, but also on palaeontological consideration, the sister group of the insects is believed to be found among the myriapods. Using nuclear ribosomal gene sequences for constructing a molecular phylogeny, we provide strong evidence that the crustaceans and not the myriapods should be considered to be the sister group of the insects. Moreover, the degree of sequence divergence suggests that the diversification of the myriapods occurred during the Cambrian. Our findings have general implications for the course of land colonization by the different arthropod groups, as well as for the interpretation of primitive and derived features of arthropod morphology.

Animals↗
PubMed1995

Evolution of segmentation genes in insects.

Systematic genetic analysis of the segmentation process in Drosophila has established a paradigm for the molecular control of the formation of metameric segments. However, it has been suggested that some of the mechanisms involved in this process in Drosophila are uniquely adapted to the syncytial mode of embryogenesis in such higher dipterans. A particularly contentious problem is the role of early segmentation genes in short-germ insects, in which development proceeds by sequential addition of segments in a cellular environment. However, analysis of the expression of presumptive homologs of segmentation genes in holometabolous short-germ insects suggests that they do indeed have a role in segmentation and that the Drosophila paradigm may be more widely applicable than is usually assumed. Most interestingly, these results suggest that the molecular mechanisms of pattern formation in noncellular and in cellular environments may not be as radically different as it is often thought to be.

Animals↗
PubMed1995

Conserved and divergent expression aspects of the Drosophila segmentation gene hunchback in the short germ band embryo of the flour beetle Tribolium.

The segmentation gene hunchback (hb) plays a central role in determining the anterior-posterior pattern in the Drosophila embryo. We have cloned the homologue of hb from the flour beetle Tribolium and show that, on the basis of its expression pattern, most of its functions seem to be conserved between these two species. Like Drosophila, Tribolium has a maternal hb expression that appears to be under translational control by a factor at the posterior pole of the embryo. The maternal expression is followed by a zygotic expression in the region of the developing head and thoracic segments. During germ band extension, a posterior expression domain appears that is likely to be homologous to the posterior blastoderm expression of hb in Drosophila. These observations suggest that hb may have the same functions in early Drosophila and Tribolium development, despite the different types of embryogenesis in these two species (long versus short germ development). One differing aspect of hb expression in Tribolium concerns a structure that is not present in Drosophila, namely the serosa. An hb expression domain at the anterior pole precisely demarcates the border between the extraembryonic serosa and the embryonic field in the Tribolium embryo at an early stage, and hb protein remains expressed in the serosa cells until the end of embryogenesis.

Amino Acid Sequence↗
PubMed1995

Zygotic caudal regulation by hunchback and its role in abdominal segment formation of the Drosophila embryo.

caudal (cad) is a maternally and zygotically expressed gene in Drosophila whereby the two phases of expression can functionally replace each other. The zygotic expression forms an abdominal and a posterior domain, whereby only the posterior domain has so far been studied with respect to its regulation and function. We show here that the abdominal cad domain is regulated by the hunchback (hb) gradient through repression at high concentrations and activation at low concentrations of HB protein. To study the function of the abdominal cad domain in the absence of redundant interactions, we have utilized an experimental system in which the embryo lacks the normal bicoid (bcd) and hb expression. An artificial hb gradient is then introduced into such embryos, which results in an induction of an ectopic zygotic cad domain in the more anterior region. Employing this system, we show that the cad domain functions by activating the expression of the abdominal gap genes knirps (kni) and giant (gt). We conclude that cad is the so far missing region-specific activator of abdominal segmentation genes.

Abdomen↗
PubMed1994

Chromosomal homogeneity of Drosophila ribosomal DNA arrays suggests intrachromosomal exchanges drive concerted evolution.

BACKGROUND: The individual copies of tandemly repeated genes, such as ribosomal DNA (rDNA), evolve coordinately within a species. This phenomenon has been called concerted evolution, and is thought to be caused by sequence-homogenizing mechanisms, such as gene conversion or unequal crossing-over between individual copies of the gene family. As these processes would act between the arrays on homologous and non-homologous chromosomes, the whole family of repeats would be expected to undergo homogenization in a given interbreeding population. RESULTS: In order to study the homogenization process, we have examined polymorphisms within the internal transcribed spacer (ITS) of the rDNA in populations of Drosophila melanogaster at the sequence level, by DNA sequencing and temperature-gradient gel electrophoresis. Among 84 ITS clones sequenced from five different wild-type strains, we found three polymorphic sites that are apparently in the process of homogenization. However, these three sites, as well as combinations of them, occurred at different frequencies in the different strains. Moreover, temperature-gradient gel electrophoresis analysis of an ITS fragment including these three sites shows that single chromosomes from locally interbreeding populations can harbor rDNA arrays that are largely homogenized for different sequence variants. CONCLUSIONS: The presence of chromosomal arrays that are homogeneous for different variants in interbreeding populations of Drosophila melanogaster indicates that there is little recombination between the chromosomes while new mutations are being homogenized along the individual arrays. The most likely explanation for this finding is that intrachromosomal recombination events occur at much higher rates than recombination between homologous chromosomes. Thus, the first step of the homogenization process would occur mainly within chromosomal lines. Such behavior of tandem repeat arrays suggests a simple explanation of how selection can act on a multigene family, namely by acting on whole chromosomally confined repeat arrays rather than on individual repeat units.

Animals↗
PubMed1994

Sympatric speciation suggested by monophyly of crater lake cichlids.

The existence of sympatric speciation--that populations diverge into species in the absence of physical or ecological barriers--is controversial. The East African Great Lakes harbour hundreds of cichlid species representing only a few monophyletic lineages, although palaeolimnological evidence and local restrictions on species distribution suggest that speciation in these lakes could have been allopatric. The case for sympatry in restricted areas of Lakes Malawi and Tanganyika is stronger but not unassailable. A better case might be made for cichlid species flocks in small, ecologically monotonous crater lakes. Here we present a mitochondrial DNA analysis of cichlid species flocks endemic to two such lakes in Cameroon. The results suggest that the flocks in each lake are monophyletic: the implication being that each lake was colonized once only, the size and shape of each lake being such that subsequent diversification would have been sympatric.

Animals↗
PubMed1994

Insect calcium channels. Molecular cloning of an alpha 1-subunit from housefly (Musca domestica) muscle.

The complete amino acid sequence of an invertebrate calcium channel alpha 1-subunit from housefly (Musca domestica) larvae (designated Mdl alpha 1) has been deduced by cDNA cloning and sequence analysis. Mdl alpha 1 shares higher percent sequence identity with 1,4-dihydropyridine (DHP)-sensitive L-type than with DHP-insensitive calcium channels. As shown by whole mount in situ hybridization and immunostaining Mdl alpha 1 is predominantly expressed in the larval body wall musculature.

Amino Acid Sequence↗
PubMed1994

Expression patterns of twist and snail in Tribolium (Coleoptera) suggest a homologous formation of mesoderm in long and short germ band insects.

The mesodermal region in Drosophila is determined by a maternally derived morphogenetic gradient system which specifies the different cell fates along the dorsoventral axis, including the prospective mesodermal cells at the ventral side of the embryo. There are at least two zygotic target genes, twist and snail, which are required for mesoderm formation in Drosophila. To analyze whether a similar mode of mesoderm specification might also apply to short germband insect embryos, we have cloned twist and snail-related gene fragments from the flour beetle Tribolium and have analyzed their expression pattern. Both genes are expressed in a ventral stripe at early blastoderm stage, which is restricted to the region of the developing germ rudiment. The cells expressing the two genes are those that invaginate during gastrulation, indicating that the early stages of mesoderm specification are indeed very similar between the two species. Interestingly, both genes are also expressed during germband extension in a subregion of the growth zone of the embryo which forms the mesodermal cells. This suggests that the expression of the two genes is required for mesoderm formation both at early blastoderm stage and during germband elongation until the end of the segmental growth process.

Amino Acid Sequence↗