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D Tautz

Publications and source records attributed to D Tautz.

At least 73 records · Page 4Linked to original sources
PubMed1994

Evolutionary analysis of genes involved in early embryonic pattern formation in Drosophila.

Segmentation and homeotic genes have originally been identified and analyzed in Drosophila. Molecular techniques such as low stringency hybridization or PCR now allow to clone homologs of these genes from different organisms. This provides a basis to study the evolution of pattern formation mechanisms between organisms at the gene level, creating a new discipline: molecular comparative embryology. This chapter discusses the practical and conceptual problems arising from this approach.

Animals↗
PubMed1994

Regulatory and coding regions of the segmentation gene hunchback are functionally conserved between Drosophila virilis and Drosophila melanogaster.

The segmentation gene hunchback (hb) is involved in setting up the anterior-posterior axis of the Drosophila embryo. It is expressed maternally and zygotically and it plays a key role in integrating the effects of the anterior and posterior maternal systems. The hb gene from D. virilis has previously been cloned and was shown to be well conserved in its coding region, but less so in its upstream region which shows a more patchy pattern of conserved and diverged sequences. This work deals with the functional conservation of hb between the two species. We have mapped two additional regulatory elements for the expression of hb in the early embryo, namely the enhancer for the maternal expression and the enhancer region for the late blastoderm expression. Fragments containing these two elements, the previously identified bicoid dependent element for the early blastoderm expression of hb and the coding region were taken from D. virilis and tested in the D. melanogaster background. We find that all enhancer elements as well as the coding region are functionally conserved between the two species. Comparison of the upstream sequences that include the enhancer region for the late blastoderm expression reveal seven highly conserved blocks. Some of these contain consensus binding sites for transregulatory factors that are likely to control the respective expression domains.

Amino Acid Sequence↗
PubMed1994

Simple sequences.

Simple sequences (or microsatellites) are stretches of monotonous repetitions of short (1-5bp) nucleotide motifs that are distributed across the whole genome in eukaryotes. They are probably generated by slippage during replication and their primary mutation rate seems to be controlled predominantly by the efficiency of the mismatch repair system. Although most mutations in simple sequence loci appear to be neutral, some mutations in particular stretches have been implicated as having a role in human genetic diseases.

Animals↗
PubMed1994

Differential regulation of target genes by different alleles of the segmentation gene hunchback in Drosophila.

hunchback (hb) is a key regulatory gene in the early segmentation gene hierarchy of Drosophila. It codes for a transcription factor of the Cys2-His2 zinc finger type and shows two separate zinc finger domains in its coding region. hb forms a morphogenetic gradient in the middle of the embryo that is required for setting the spatial boundaries of several target genes. We have analyzed the molecular lesions found in the different hb alleles and have studied the differential effects of these alleles on a number of such target genes. We find that in mutants in which the HB protein lacks a functional second finger domain, the regulation of the target genes Krüppel (Kr) and knirps (kni) is differentially affected. While this domain is required for the correct regulation of Kr, it is not necessary for the repression of kni. Furthermore, mutations affecting this domain lead to a decreased protein stability. The integration of the expression pattern of target genes was found to be distorted in a second class of mutants between the two finger domains which lead to gain of function or neomorphic phenotypes. The effects of these mutations were studied in detail and it was found that they fall into two classes, the first one interfering with the function of the maternal hb product, the second leading to a delayed segmentation. The function of the latter class appears to be linked to the secondary expression of hb in the parasegment 4 (PS4) stripe at blastoderm stage.

Alleles↗
PubMed1994

Comparative evolutionary analysis of rDNA ITS regions in Drosophila.

The internal transcribed spacer (ITS) of the ribosomal DNA is generally considered to be under low functional constraint, and it is therefore often treated as a typical nonfunctional spacer sequence. We have analyzed the ITS regions of five species from the Drosophila melanogaster subgroup, two Drosophila species from outside this group (D. pseudoobscura and D. virilis), as well as from the more distantly related dipteran fly Musca domestica. The sequence comparisons show a distinctive conservation/divergence pattern, indicating that some regions are more conserved than others. Moreover, secondary-structure calculations indicate several conserved structural elements within the ITS regions. On the other hand, a statistical test that allows us to estimate the fraction of sites that are not under selective constraint suggests that more than half of the spacer is apparently free to diverge and evolves with a rate that is close to the neutral rate of sequence evolution in Drosophila. The ITS sequences can be used to derive a molecular phylogeny for the species under study. We find that the ITS tree is largely in line with the so-far-known phylogeny of this group of species, with one difference. The species most distant within the D. melanogaster subgroup is D. yakuba, rather than D. orena, as is normally assumed.

Animals↗
PubMed1994

Low genetic variability in a natural alpine marmot population (Marmota marmota, Sciuridae) revealed by DNA fingerprinting.

Genetic heterogeneity is usually considered an important factor for the viability of a population, yet there are cases in which populations sustain themselves despite virtual homozygosity. A prior step to studying the effects of such low levels of genetic variability can be the analysis of its causes. We analysed a population of the highly social alpine marmot (Marmota marmota, Sciuridae) by multilocus DNA fingerprinting. The fingerprint patterns revealed a very low degree of polymorphism in our main study population. We show that this lack of hypervariability is caused by a low effective population size, rather than by an unusual low mutation rate of the fingerprint loci studied. However, the current number of breeding pairs was found to be about an order of magnitude larger than the one that would be expected to lead to such a low degree of heterozygosity. We conclude that there must have been bottlenecks in the history of the Berchtesgaden marmot population that have severely affected its genetic heterozygosity.

Animals↗
PubMed1994

Autonomous concentration-dependent activation and repression of Krüppel by hunchback in the Drosophila embryo.

The subdivision of the anterior-posterior axis in Drosophila is achieved by a cascade of spatially regulated transcription factors which form short-range gradients at the syncytial blastoderm stage. These factors are assumed to have concentration-dependent regulatory effects on their target genes. However, there is so far little direct in vivo evidence that a single factor can autonomously activate and repress a given target gene. We have analysed here the regulatory capabilities of the gap gene hunchback by creating an artificial gradient of hunchback in the early embryo. This was achieved by providing the maternally expressed mRNA of hunchback with the anterior localization signal of the bicoid RNA. The effects of this artificial hunchback gradient were then studied in different types of mutant background. We show that under these conditions hb is autonomously capable of activating the target gene Krüppel at low concentrations and repressing it at high concentrations. In addition, we show that the artificially created hunchback gradient can organize a large part of the segment pattern, although it is expressed at a different position and in a different shape than the wild-type gradient of hunchback.

Animals↗
PubMed1993

Social structure of pilot whales revealed by analytical DNA profiling.

Long-finned pilot whales swim in large, extremely cohesive social groups known as pods. Molecular typing revealed that pod members form a single extended family. Mature males neither disperse from nor mate within their natal pods, a situation unusual for mammals. Such behavior could be explained in terms of inclusive fitness benefits gained by adult males helping the large number of female relatives with which they swim.

Alleles↗
PubMed1993

Involvement of an orthologue of the Drosophila pair-rule gene hairy in segment formation of the short germ-band embryo of Tribolium (Coleoptera)

The segments in long germ-band insect embryos, like Drosophila, are all determined at syncytial blastoderm stage. This is in contrast to short germ-band embryos which show an early determination of only the anterior head segments, whereas the more posterior thoracic and abdominal segments are sequentially added after formation of a primary germ anlage (reviewed in ref. 1). Segment formation in Drosophila involves the pair-rule genes which define double segmental periodicities and which have been considered to represent a special adaptation to the long germ-band type development hairy belongs to the primary pair-rule genes in Drosophila which are directly regulated by the gap genes, such as Krüppel. We have isolated the orthologues of hairy and Krüppel from the flour beetle Tribolium castaneum which has a short germ type development. We show here that hairy is expressed in several stripes at blastoderm stage and later on in two stripes in the growth zone of the developing embryo. Krüppel expression overlaps hairy stripe three and four expression, very similar to Drosophila. This suggests that the segment patterning mechanism that acts in an open blastoderm in Drosophila works in a similar way in the cellularized Tribolium embryo.

Amino Acid Sequence↗
PubMed1993

Notes on the definition and nomenclature of tandemly repetitive DNA sequences.

Tandemly repetitive DNA is a major component of all eukaryotic genomes. This fact has been known for almost 30 years and research on this class of DNA is still being done. Its biology and evolution are therefore now becoming fairly well understood. DNA-fingerprint techniques rely very much on this knowledge. However, the large amount of research on these sequences has inevitably led to a large number of different concepts and theories about their nature. This has also resulted in some confusion as to the nomenclature. The following notes are intended to resolve this confusion somewhat and to give some definitions for the major classes of tandemly repetitive DNA.

Animals↗
PubMed1992

Evolutionary conservation pattern of zinc-finger domains of Drosophila segmentation genes.

A number of genes of the developmental gene hierarchy in Drosophila encode transcription factors containing Cys2His2 zinc finger domains as DNA-binding motifs. To learn more about the evolution of these genes, it is necessary to clone the homologs, or more correctly the orthologs, from different species. Using PCR, we were able to obtain apparently orthologous fragments of hunchback (hb), Krüppel (Kr), and snail (sna) from a variety of arthropods and partly also from other animal phyla. Sequence alignments of these fragments show that the amino acid differences can normally not be correlated with the evolutionary distances of the respective species. This is due to an apparent saturation of potential replacements within the finger domains, which is also evident from the frequent occurrence of convergent replacements. Another recurrent feature of these alignments is that those amino acids that are directly involved in determining the DNA-binding specificity of the fingers are most conserved. Using in vitro bandshift experiments we can indeed show that the binding specificity of a hunchback finger fragment from different species is not changed. This implies that there is a high selective pressure to maintain the regulatory target elements of these genes during evolution.

Amino Acid Sequence↗
PubMed1992

Slippage synthesis of simple sequence DNA.

The analysis of slippage synthesis of simple sequence DNA in vitro sheds some light on the question of how simple sequences arise in vivo. We show that it is possible to synthesize all types of repetitious di- and trinucleotide motifs starting from short primers and a polymerase in vitro. The rate of this synthesis depends on a sequence specific slippage rate, but is independent of the length of the fragments being synthesized. This indicates that only the ends of the DNA fragments are involved in determining this rate and that slippage is accordingly a short range effect. Slippage synthesis occurs also on a fixed template where only one strand is free to move, a situation which resembles chromosome replication in vivo. It seems therefore likely that slippage during replication is the cause of the observed length polymorphism of simple sequence stretches between individuals of a population.

Base Sequence↗
PubMed1992

Redundancies, development and the flow of information.

There is increasing evidence for the wide-spread existence of functionally redundant genetic pathways in developmental processes. However, both their significance and manner of evolution are still matters of debate. I will argue here that redundancy of gene actions may, in fact, be a necessary requirement for the development and evolution of complex life forms. One can view development as a process that transmits information from the egg to the adult organism. Transmission of information is, however, always an error-prone process, which can only be safeguarded by including redundancies in the message. Molecular examples for well analysed redundant processes indicate that redundancies may best be understood within a conceptual framework of overlaps between different gene functions.

Animals↗
PubMed1991

Conservation of polymorphic simple sequence loci in cetacean species.

Length polymorphisms within simple-sequence loci occur ubiquitously in non-coding eukaryotic DNA and can be highly informative in the analysis of natural populations. Simple-sequence length polymorphisms (SSLP) in the long-finned pilot whale Globicephala melas (Delphinidae) have provided useful information on the mating system as well as on the genetic structure of populations. We have therefore tested whether the polymerase chain reaction primers designed for Globicephala could also be used to uncover variability in other whale species. Homologous loci could indeed be amplified from a diverse range of whales, including all toothed (Odontoceti) and baleen whales (Mysticeti) tested. Cloning and sequencing these loci from 11 different species revealed an unusually high conservation of sequences flanking the simple-sequence stretches, averaging 3.2% difference over 35-40 Myr. This represents the lowest divergence rate for neutral nucleotide positions found for any species group so far and raises the possible need for a re-evaluation of the age of the modern whales. On the other hand, the high conservation of non-coding sequences in whales simplifies the application of SSLP DNA fingerprinting in cetacean species, as primers designed for one species will often uncover variability in other species.

Animals↗
PubMed1991

Gap genes and gradients--the logic behind the gaps.

Gap genes stand at the top of the zygotic segmentation hierarchy in Drosophila. Their expression domains are set up by a combination of maternal regulatory signals and interactions among themselves. In addition, these regulatory pathways are partially redundantly specified by the maternal and zygotic genomes, or by multiple zygotic gene products. The gap genes code for transcription factors which exert their function by forming short-range morphogenetic gradients; differential concentrations of these transcription factors can either act as activators or as repressors for the expression domains of neighboring genes. It is possible to view the gap genes as a system of genes that subdivides the embryo by forming an activation-repression cascade proceeding from anterior towards posterior.

Animals↗
PubMed1991

Segmentation gene expression in the housefly Musca domestica.

Drosophila and Musca both belong to the group of higher dipteran flies and show morphologically a very similar early development. However, these two species are evolutionary separated by at least 100 million years. This presents the opportunity for a comparative analysis of segmentation gene expression across a large evolutionary distance in a very similar embryonic background. We have analysed in detail the early expression of the maternal gene bicoid, the gap genes hunchback, Krüppel, knirps and tailless, the pair-rule gene hairy, the segment-polarity gene engrailed and the homoeotic gene Ultrabithorax. We show that the primary expression domains of these genes are conserved, while some secondary expression aspects have diverged. Most notable is the finding of hunchback expression in 11-13 stripes shortly before gastrulation, as well as a delayed expression of terminal domains of various genes. We conclude that the early developmental gene hierarchy, as it has been defined in Drosophila, is evolutionary conserved in Musca domestica.

Animals↗