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C Nüsslein-Volhard

Publications and source records attributed to C Nüsslein-Volhard.

At least 91 records · Page 5Linked to original sources
PubMed1991

Determination of the embryonic axes of Drosophila.

The principles of embryonic pattern formation have been studied extensively in many systems using classical experimental approaches. In Drosophila, a powerful combination of genetics and transplantation experiments, as well as molecular biology, have helped to elucidate the mechanisms that operate during oogenesis and early embryogenesis to establish a set of positional cues required for axis determination in the early embryo. In systematic searches for maternal effect mutations a small number of about 30 genes have been identified that specifically affect the process of determination of the embryonic axes. These 'coordinate' genes define four systems that determine the anteroposterior (AP) axis (three systems) and the dorsoventral (DV) axis (one system) independently. In the anteroposterior axis, the anterior system determines the segmented region of head and thorax, the posterior system determines the segmented abdominal region, and the terminal system is responsible for the formation of the nonsegmented termini at the anterior and posterior egg tips, the acron and telson. In contrast, pattern along the dorsoventral axis is determined by one system only. Although all four systems use different biochemical mechanisms, they share several properties. (1) The product of one gene in each system is localized in a specific region of the freshly laid egg and functions as a spatial signal. (2) In each system, this spatial information finally results in the asymmetrical distribution of one gene product that functions as a transcription factor. (3) This transcription factor is distributed in a concentration gradient that defines the spatial limits of expression of one or more zygotic target genes. The combined action of these three anteroposterior systems as well as the dorsoventral system defines the expression of zygotic target genes in at least seven distinct regions along the anteroposterior and at least three in the dorsoventral axis. These longitudinal and transverse domains provide a coarse spatial prepattern which is then further refined by the action and interaction of zygotic pattern genes.

Animals↗
PubMed1990

Localized requirement for torso-like expression in follicle cells for development of terminal anlagen of the Drosophila embryo.

The torso (tor) gene, one of six identified maternal genes essential for the development of the anterior and posterior terminal structures in the Drosophila embryo, is likely to function as a transmembrane receptor tyrosine kinase. Although tor protein is uniformly distributed in the membrane of the egg cell and syncytial embryo, genetic and molecular data suggest that tor is locally activated at the ends of the embryo by a ligand present in the perivitelline space. Local activation of tor could be achieved if the ligand were expressed by a subpopulation of the follicle cells that surround the developing oocyte. Here we describe torso-like (tsl), the sixth member of the terminal gene class, and show that it is unique among these genes in that its expression is required in the somatic follicle cells rather than in the germ line. Moreover, mosaic analysis demonstrates that tsl expression is necessary only in subpopulations of follicle cells located at the poles of the oocyte. Thus, the spatially regulated expression of tsl in the follicle cell layer may generate a localized signal that is transduced by tor, ultimately resulting in the formation of the terminal structures of the embryo.

Animals↗
PubMed1990

Autonomous determination of anterior structures in the early Drosophila embryo by the bicoid morphogen.

A small number of maternal effect genes determine anterior-posterior pattern in the Drosophila embryo. Embryos from females mutant for the maternal gene bicoid lack head and thorax. bcd mRNA becomes localized to the anterior tip of the egg during oogenesis and is the source for the morphogen gradient of bcd protein. Here we show that in vitro transcribed bicoid mRNA that has its own leader sequences substituted by the Xenopus beta-globin 5' untranslated sequences is translated more efficiently than bicoid mRNA with the natural 5' mRNA leader when tested in vitro and in Drosophila Schneider cells. When injected into bicoid mutant embryos, only the bcd mRNA with the beta-globin leader sequence, substituted for the natural leader, is able to induce anterior development. We used P-transformation to show that sequences in the 5' leader are neither necessary for localization of the transcript nor for the translational block of the bcd mRNA during oogenesis. For our injection experiments, we used only one of the identified splicing forms of bcd mRNA. The bcd protein species derived from this mRNA is able to induce anterior development at any position along the anterior-posterior axis. Thus bicoid protein can induce development of head and thorax independent of any other specifically localized morphogenetic factor. Our findings further support the notion that the concentration gradient of bcd protein, and not the existence of different forms of bcd protein, is responsible for specifying subregions of the embryo.

Animals↗
PubMed1989

A gradient of nuclear localization of the dorsal protein determines dorsoventral pattern in the Drosophila embryo.

The dorsoventral axis of the Drosophila embryo is determined by a morphogen gradient established by the action of 12 maternal-effect genes: the dorsal group genes and cactus. One of the dorsal group genes, dorsal (dl), encodes the putative morphogen. Although no overall asymmetry in the distribution of dorsal protein is observed, a gradient of nuclear concentration of dl protein is established during cleavage stages, with a maximum at the ventral side of the egg. At the dorsal side of the egg, the protein remains in the cytoplasm. Nuclear localization of the dl protein, and hence gradient formation, is blocked in dorsalizing alleles of all of the other dorsal group genes, while in ventralizing mutants nuclear localization extends to the dorsal side of the egg. A correlation between dl protein distribution and embryonic pattern in mutant embryos indicates that the nuclear concentration of the dl protein determines pattern along the dorsoventral axis.

Animals↗
PubMed1989

Rescue of bicoid mutant Drosophila embryos by bicoid fusion proteins containing heterologous activating sequences.

The maternal gene bicoid (bcd) determines pattern in the anterior half of the Drosophila embryo. It is reported here that the injection of bcd mutant embryos with messenger RNAs that encode proteins consisting of heterologous acidic transcriptional activating sequences fused to the DNA-binding portion of the bcd gene product, can completely restore the anterior pattern of the embryo.

Animals↗
PubMed1989

Determination of spatial domains of zygotic gene expression in the Drosophila embryo by the affinity of binding sites for the bicoid morphogen.

The maternal gene bicoid is a key component of the system that determines the pattern of the anterior half of Drosophila embryos. The bicoid protein forms a concentration gradient in early embryos, and is known to bind DNA. Specific binding sites are now shown to confer expression in a region of the embryo that depends on their affinity for bicoid protein: sites of high affinity allow expression further down the bicoid protein gradient than sites of low affinity.

Animals↗
PubMed1989

The Drosophila gene torso encodes a putative receptor tyrosine kinase.

The maternal gene torso, required for determination of anterior and posterior terminal structures in the Drosophila embryo, was cloned using P-element tagging. Genetic evidence suggests that the action of the gene product is spatially restricted to the terminal regions; the torso messenger RNA, however, is evenly distributed. Structural similarities of the predicted torso protein with growth-factor receptor tyrosine kinases suggest that the spatial restriction of torso activity results from a localized activation of the torso protein at the anterior and posterior egg pole.

Animals↗
PubMed1989

Axis determination in insect embryos.

The principles of pattern formation in insects have been studied extensively using classical experimental approaches. In Drosophila, a powerful combination of genetics and transplantation experiments, as well as molecular biology, has helped to elucidate the mechanisms that operate during oogenesis to establish a set of positional cues required for axis determination in the early embryo. These studies suggest the following model: for the anteroposterior axis of the embryo, three groups of maternal genes define three largely independent systems that determine (1) the anterior segmented region of head and thorax, (2) the posterior segmented region of the abdomen, and (3) the terminal non-segmented regions of acron and telson. In contrast, the dorsoventral egg axis appears to require only one system. In each of the four systems, one key gene has an active product that is unequally distributed in the egg. This product provides the spatial signal for the region-specific activation of the transcription of at least one zygotic target gene. The other members within each group serve accessory functions such as determining the correct spatial distribution of the key gene products or controlling their localized activation. The unique expression patterns of the individual zygotic target genes provide a coarse spatial framework which is then refined by the action and interaction of zygotic genes. The notion of three independent systems determining the anteroposterior axis is at variance with a previous model (Meinhardt 1977, Nüsslein-Volhard 1979) of only one gradient, with a high point at the posterior pole, determining a series of states in a concentration-dependent manner. Concentration-dependent determination of more than one quality is likely to occur in the anterior and the dorsoventral system. In contrast, position and polarity within the posterior pattern appear to depend largely on the interaction between gap genes expressed in neighbouring regions rather than on the concentration of the posterior signal.

Animals↗
PubMed1989

Multiple steps in the localization of bicoid RNA to the anterior pole of the Drosophila oocyte.

The anterior region of the Drosophila embryonic pattern is determined by a gradient of the bicoid (bcd) protein. The correct formation of this gradient requires the localization of bcd RNA to the anterior pole of the egg. Here we use a wholemount in situ technique to examine the process of bcd RNA localization during oogenesis and embryogenesis. While bcd protein becomes distributed in a gradient that extends throughout the anterior two thirds of the early embryo, bcd RNA remains restricted to a much smaller region at the anterior pole. The difference between these distributions indicates that the shape of the protein gradient must depend to some extent on the posterior movement of the protein after it has been synthesized. Four distinct phases of bcd RNA localization can be distinguished during oogenesis. Between stages 6 and 9 of oogenesis, the RNA accumulates in a ring at the anterior end of the oocyte. During the second phase, in stage 9-10a follicles, the RNA also localizes to the apical regions of the nurse cells, demonstrating that the nurse cells possess an intrinsic polarity. As the nurse cells contract during stages 10b-11, all of the bcd RNA becomes localized to the cortex at the anterior end of the oocyte. During a final phase that must occur between stage 12 of oogenesis and egg deposition, the RNA becomes localized to a spherical region that occupies a slightly dorsal position at the anterior pole.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Function of torso in determining the terminal anlagen of the Drosophila embryo.

The formation of the unsegmented terminal regions of the Drosophila larva, acron and telson requires the function of at least five maternal genes (terminal genes class). In their absence, the telson and acron are not formed. One of them, torso (tor), has gain-of-function alleles which have an opposite phenotype to the lack-of-function (tor-) alleles: the segmented regions of the larval body, thorax and abdomen, are missing, whereas the acron is not affected and the telson is enlarged. In strong gain-of-function mutants, the pair-rule gene fushi tarazu (ftz) is not expressed, demonstrating the suppression of the segmentation process in an early stage of development. The tor gain-of-function effect is neutralized, and segmentation is restored in double mutants with the zygotic gene tailless (tll), which has a phenotype similar (but not identical) to that of tor-. This suggests that tor acts through tll, and that in the gain-of-function alleles of tor, the tll gene product is ectopically expressed at middle positions of the embryo, where it inhibits the expression of segmentation genes like ftz.

Animals↗
PubMed1988

A gradient of bicoid protein in Drosophila embryos.

The maternal gene bicoid (bcd) organizes anterior development in Drosophila. Its mRNA is localized at the anterior tip of the oocyte and early embryo. Antibodies raised against bcd fusion proteins recognize a 55-57 kd doublet band in Western blots of extracts of 0-4 hr old embryos. This protein is absent or reduced in embryonic extracts of nine of the 11 bcd alleles. The protein is concentrated in the nuclei of cleavage stage embryos. It cannot be detected in oocytes, indicating temporal control of bcd mRNA translation. The bcd protein is distributed in an exponential concentration gradient with a maximum at the anterior tip, reaching background levels in the posterior third of the embryo. The gradient is probably generated by diffusion from the local mRNA source and dispersed degradation.

Alleles↗
PubMed1988

The bicoid protein determines position in the Drosophila embryo in a concentration-dependent manner.

The bicoid (bcd) protein in a Drosophila embryo is derived from an anteriorly localized mRNA and comes to be distributed in an exponential concentration gradient along the anteroposterior axis. To determine whether the levels of bcd protein are directly related to certain cell fates, we manipulated the density and distribution of bcd mRNA by genetic means, measured the resultant alterations in height and shape of the bcd protein gradient, and correlated the gradient with the fate map of the respective embryos. Increases or decreases in bcd protein levels in a given region of the embryo cause a corresponding posterior or anterior shift of anterior anlagen in the embryo. The bcd protein thus has the properties of a morphogen that autonomously determines positions in the anterior half of the embryo.

Animals↗
PubMed1988

The role of localization of bicoid RNA in organizing the anterior pattern of the Drosophila embryo.

The organization of the anterior pattern in the Drosophila embryo is mediated by the maternal effect gene bicoid. bcd has been identified in an 8.7-kb genomic fragment by germ line transformants that completely rescue the mutant phenotype. The major transcript of 2.6 kb includes a homeobox with low homology to previously known homeoboxes, a PRD-repeat and a M-repeat. In situ hybridizations reveal that bcd is transcribed in the nurse cells. The mRNA is localized at the anterior tip of oocyte and early embryo until the cellular blastoderm stage. The localization of the transcript requires the function of the maternal effect genes exuperantia and swallow while transcript stability is reduced by functions depending on posterior group genes.

Alleles↗
PubMed1988

A group of genes required for pattern formation in the ventral ectoderm of the Drosophila embryo.

Mutations in the genes spitz (spi), Star (S), single-minded (sim), pointed (pnt), rhomboid (rho) (all zygotic), and sichel (sic) (maternal), collectively called the spitz group, cause similar pattern alterations in ventral ectodermal derivatives of the Drosophila embryo. The cuticle structures lacking in mutant embryos normally derive from longitudinal strips of the ventro-lateral blastoderm. Defects were found in the median part of the central nervous system in whole-mount embryos stained with anti-HRP (horseradish peroxidase) antibodies. In addition, the nerve cells expressing the even-skipped protein appeared abnormally arranged. These results suggest that groups of cells from the same region, including both epidermal and neural precursor cells, require spitz-group gene activity for normal development. The members of the spitz group differ from one another: sim affects a more median strip of the ventral ectoderm than the other zygotic genes and pnt causes separation rather than deletion of pattern elements. As shown by pole cell transplantations, spi and S are also required for normal development of the female germ line, while sim, rho, and pnt appear to be exclusively zygotically expressed, and the maternal gene sic acts in the germ line autonomously. Some embryos produced by sic-homozygous females differentiate the spitz phenotype, others develop normally or die early. Of all the spitz-group genes, sim appears to have the most specific effect on the embryonic pattern. The significance of the spitz-group phenotypes for the dorso-ventral pattern formation is discussed.

Animals↗
PubMed1987

Determination of anteroposterior polarity in Drosophila.

The principles of pattern formation in embryogenesis can be studied in Drosophila by means of a powerful combination of genetic and transplantation experiments. The segmented pattern of the Drosophila embryo is organized by two activities localized at the anterior and posterior egg poles. Both activities exert inducing and polarizing effects on the pattern when transplanted to other egg regions. A small set of maternal genes have been identified that are required for these activities. Mutants in these genes lack either the anterior or posterior part of the segmented pattern. The unsegmented terminal embryonic regions require a third class of genes and form independently of the anterior and posterior centers.

Animals↗
PubMed1987

hunchback, a gene required for segmentation of an anterior and posterior region of the Drosophila embryo.

The locus hunchback (hb) is a member of the gap class of segmentation genes of Drosophila. A number of X-ray-induced deletions locate the hb locus at the chromosomal site 85A3-B1, to the right of the pink locus, which maps in the same interval. A total of 14 EMS and 3 X-ray-induced hb alleles have been studied. Homozygous mutant embryos show deletions of segments in two separate regions. In the six strong alleles, the labium and all three thoracic segments are deleted anteriorly while posteriorly the 8th abdominal segment and adjacent parts of the 7th abdominal segment are lacking. The eight weak alleles show smaller deletions both in the thoracic and posterior abdominal region. In the weakest allele only part of the mesothorax is deleted. Three hb alleles produce a homoeotic transformation: superimposed on a strong or weak deletion phenotype, head or thoracic segments are transformed into abdominal segments, respectively. This suggests that hb might also be involved in the regulation of genes in the Bithorax complex (BX-C). Fate mapping of the normal-appearing segments in strong mutant embryos using the UV-laser beam ablation technique (Lohs-Schardin et al., 1979) shows that these segments arise from the normal blastoderm regions. The mutant phenotype can be recognized soon after the onset of gastrulation in a failure to fully extend the germ band. In 6-hr-old mutant embryos, two clusters of dead cells are observed in the thoracic and posterior abdominal region. These observations indicate region specific requirement of hb gene function. The analysis of germ line chimeras by transplantation of homozygous mutant pole cells shows that hb is already expressed during oogenesis. Homozygous mutant embryos derived from a homozygous mutant germ line have a novel phenotype. The anterior affected region is enlarged, including all three gnathal segments and the anterior three abdominal segments. In addition three abdominal segments with reversed polarity are formed between the remaining head structures and the posterior abdomen. Heterozygous mutant embryos derived from a homozygous mutant germ line develop normally, indicating that maternal gene expression is not required for normal development.

Abdomen↗
PubMed1986

Abdominal segmentation, pole cell formation, and embryonic polarity require the localized activity of oskar, a maternal gene in Drosophila.

Embryos derived from oskar females lack pole cells and the specialized pole plasm including polar granules. In addition, the abdominal region remains unsegmented and eventually dies. Transplantation of cytoplasm from normal embryos into mutant embryos reveals that osk-dependent activity is strictly localized at the posterior pole and has three distinct functions. In mutant embryos the activity will normalize pole cell formation when transplanted into the posterior pole and abdominal segmentation after transplantation to a more anterior, the prospective abdominal, region. Furthermore, osk activity can provoke the formation of a second "posterior center" at the anterior. The participation of the osk product in the establishment of a source of morphogenetic activity in the posterior pole plasm is discussed.

Abdomen↗