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C Nüsslein-Volhard

Publications and source records attributed to C Nüsslein-Volhard.

At least 19 recordsLinked to original sources
PubMed1999

Origin and development of the zebrafish endoderm.

The segregation of cells into germ layers is one of the earliest events in the establishment of cell fate in the embryo. In the zebrafish, endoderm and mesoderm are derived from cells that involute into an internal layer, the hypoblast, whereas ectoderm is derived from cells that remain in the outer layer, the epiblast. In this study, we examine the origin of the zebrafish endoderm and its separation from the mesoderm. By labeling individual cells located at the margin of the blastula, we demonstrate that all structures that are endodermal in origin are derived predominantly from the more dorsal and lateral cells of the blastoderm margin. Frequently marginal cells give rise to both endodermal and mesodermal derivatives, demonstrating that these two lineages have not yet separated. Cells located farther than 4 cell diameters from the margin give rise exclusively to mesoderm, and not to endoderm. Following involution, we see a variety of cellular changes indicating the differentiation of the two germ layers. Endodermal cells gradually flatten and extend filopodial processes forming a noncontiguous inner layer of cells against the yolk. At this time, they also begin to express Forkhead-domain 2 protein. Mesodermal cells form a coherent layer of round cells separating the endoderm and ectoderm. In cyclops-mutant embryos that have reduced mesodermal anlage, we demonstrate that by late gastrulation not only mesodermal but also endodermal cells are fewer in number. This suggests that a common pathway initially specifies germ layers together before a progressive sequence of determinative events segregate endoderm and mesoderm into morphologically distinct germ layers.

Animals↗
PubMed1998

Zebrafish touch-insensitive mutants reveal an essential role for the developmental regulation of sodium current.

Developmental changes in neuronal connectivity and membrane properties underlie the stage-specific appearance of embryonic behaviors. The behavioral response of embryonic zebrafish to tactile stimulation first appears at 27 hr postfertilization. Because the touch response requires the activation of mechanosensory Rohon-Beard neurons, we have used whole-cell recordings in semi-intact preparations to characterize Rohon-Beard cell electrical membrane properties in several touch-insensitive mutants and then to correlate the development of excitability in these cells with changes in wild-type behavior. Electrophysiological analysis of mechanosensory neurons of touch-insensitive zebrafish mutants indicates that in three mutant lines that have been examined the sodium current amplitudes are reduced, and action potentials either have diminished overshoots or are not generated. In macho mutants the action potential never overshoots, and the sodium current remains small; alligator and steifftier show similar but weaker effects. The effects are specific to sodium channel function; resting membrane potentials are unaffected, and outward currents of normal amplitude are present. Developmental analysis of sodium current expression in mechanosensory neurons of wild-type embryos indicates that, during the transition from a touch-insensitive to a touch-sensitive embryo, action potentials acquire larger overshoots and briefer durations as both sodium and potassium currents increase in amplitude. However, in macho touch-insensitive mutants, developmental changes in action potential overshoot and sodium current are absent despite the normal regulation of action potential duration and potassium current. Thus, the maturation of a voltage-dependent sodium current promotes a behavioral response to touch. A study of these mutants will allow insight into the genes controlling the maturation of the affected sodium current.

Action Potentials↗
PubMed1998

Zebrafish segmentation and pair-rule patterning.

Segmentation in the vertebrate embryo is evident within the paraxial mesoderm in the form of somites, which are repeated structures that give rise to the vertebrae and muscle of the trunk and tail. In the zebrafish, our genetic screen identified two groups of mutants that affect somite formation and pattern. Mutations of one class, the fss-type mutants, disrupt the formation of the anterior-posterior somite boundaries during somitogenesis. However, segmentation within the paraxial mesoderm is not completely eliminated in these mutants. Irregular somite boundaries form later during embryogenesis and, strikingly, the vertebrae are not fused. Here, we show that formation of the irregular somite boundaries in these mutants is dependent upon the activity of a second group of genes, the you-type genes, which include sonic you, the zebrafish homologue of the Drosophila segment polarity gene, sonic hedgehog. Further to characterize the defects caused by the fss-type mutations, we examined their effects on the expression of her1, a zebrafish homologue of the Drosophila pair-rule gene hairy. In wild-type embryos, her1 is expressed in a dynamic, repeating pattern, remarkably similar to that of its Drosophila and Tribolium counterparts, suggesting that a pair-rule mechanism also functions in the segmentation of the vertebrate paraxial mesoderm. We have found that the fss-type mutants have abnormal pair-rule patterning. Although a her1 mutant could not be identified, analysis of a double mutant that abolishes most her1 expression suggests that a her1 mutant may not display a pair-rule phenotype analogous to the hairy phenotype observed in Drosophila. Cumulatively, our data indicate that zebrafish homologues of both the Drosophila segment polarity genes and pair-rule genes are involved in segmenting the paraxial mesoderm. However, both the relationship between these two groups of genes within the genetic heirarchy governing segmentation and the precise roles that they play during segmentation likely differ significantly between the two organisms.

Animals↗
PubMed1998

fork head domain genes in zebrafish.

Nine members of the fork head domain gene family (fkd1-fkd9) were isolated from early cDNA libraries in the zebrafish. They show unique expression patterns in whole-mount RNA in situ hybridization during the first 24 h of embryonic development. These fkd genes fall into three of ten classes, based on sequence similarities within the DNA-binding domain, whereas members for the other seven classes described in other vertebrates were not found. In addition to conserved residues at certain positions in the fork head domain, characteristic transcription activation domains as well as similarities in expression patterns were found for members of the different classes. Members of class I (fkd1/axial, fkd2/Zffkh1, fkd4 and fkd7) are differentially transcribed in unsegmented dorsal axial structures such as the floor plate, the notochord, the hypochord and, in addition, the endoderm. Transcripts of fkd3 and fkd5 (class II) are mainly detected in the cells of the ectoderm which form neural tissues, as is the case for genes of this class in other species. RNAs of the three members of class V (fkd6, fkd8 and fkd9) are expressed in the paraxial mesoderm and transiently in the neuroectoderm. fkd6 is strongly expressed in neural crest cells from early stages on, whereas fkd2 and fkd7 are transcribed in individual neural crest cells in the pharyngula period.

Amino Acid Sequence↗
PubMed1998

Genetic analysis of vertebrate sensory hair cell mechanosensation: the zebrafish circler mutants.

The molecular basis of sensory hair cell mechanotransduction is largely unknown. In order to identify genes that are essential for mechanosensory hair cell function, we characterized a group of recently isolated zebrafish motility mutants. These mutants are defective in balance and swim in circles but have no obvious morphological defects. We examined the mutants using calcium imaging of acoustic-vibrational and tactile escape responses, high resolution microscopy of sensory neuroepithelia in live larvae, and recordings of extracellular hair cell potentials (microphonics). Based on the analyses, we have identified several classes of genes. Mutations in sputnik and mariner affect hair bundle integrity. Mutant astronaut and cosmonaut hair cells have relatively normal microphonics and thus appear to affect events downstream of mechanotransduction. Mutant orbiter, mercury, and gemini larvae have normal hair cell morphology and yet do not respond to acoustic-vibrational stimuli. The microphonics of lateral line hair cells of orbiter, mercury, and gemini larvae are absent or strongly reduced. Therefore, these genes may encode components of the transduction apparatus.

Acoustic Stimulation↗
PubMed1997

A sponge-like structure involved in the association and transport of maternal products during Drosophila oogenesis.

Localization of maternally provided RNAs during oogenesis is required for formation of the antero-posterior axis of the Drosophila embryo. Here we describe a subcellular structure in nurse cells and oocytes which may function as an intracellular compartment for assembly and transport of maternal products involved in RNA localization. This structure, which we have termed "sponge body," consists of ER-like cisternae, embedded in an amorphous electron-dense mass. It lacks a surrounding membrane and is frequently associated with mitochondria. The sponge bodies are not identical to the Golgi complexes. We suggest that the sponge bodies are homologous to the mitochondrial cloud in Xenopus oocytes, a granulo-fibrillar structure that contains RNAs involved in patterning of the embryo. Exuperantia protein, the earliest factor known to be required for the localization of bicoid mRNA to the anterior pole of the Drosophila oocyte, is highly enriched in the sponge bodies but not an essential structural component of these. RNA staining indicates that sponge bodies contain RNA. However, neither the intensity of this staining nor the accumulation of Exuperantia in the sponge bodies is dependent on the amount of bicoid mRNA present in the ovaries. Sponge bodies surround nuage, a possible polar granule precursor. Microtubules and microfilaments are not present in sponge bodies, although transport of the sponge bodies through the cells is implied by their presence in cytoplasmic bridges. We propose that the sponge bodies are structures that, by assembly and transport of included molecules or associated structures, are involved in localization of mRNAs in Drosophila oocytes.

Animals↗
PubMed1997

The function of silberblick in the positioning of the eye anlage in the zebrafish embryo.

In zebrafish, as in other vertebrates, an initially singular eye field within the neural plate has to split during morphogenesis to allow the development of two separated eyes. It has been suggested that anterior progression of midline tissue within the neural plate is involved in the bilateralization of the eye field. Mutations in the recently identified silberblick (slb) gene cause an incomplete separation of the eyes. During gastrulation and early somitogenesis, the ventral midline of the central nervous system (CNS) together with the underlying axial mesendoderm is shortened and broadened in slb embryos. While in wild-type embryos the ventral CNS midline extends to the anterior limit of the neural plate at the end of gastrulation, there is a gap between the anterior tip of the ventral CNS midline and the anterior edge of the neural plate in slb. To investigate the cause for the shortening of the ventral CNS midline in slb we determined the fate of labeled ventral CNS midline cells in wild-type and slb embryos at different stages of development. In slb, anterior migration of ventral CNS midline cells is impaired, which indicates that migration of these cells is needed for elongation of the ventral CNS midline. The anterior shortening of the ventral CNS midline in slb leads to medial instead of bilateral induction of optic stalks followed by a partial fusion of the eyes at later developmental stages. The analysis of the slb phenotype indicates that anterior migration of midline cells within the neural plate is required for proper induction and subsequent bilateralization of an initially singular eye field. These findings may therefore provide a starting point in elucidating the role of neural plate morphogenesis in positioning of the eyes.

Animals↗
PubMed1997

RNA-RNA interaction is required for the formation of specific bicoid mRNA 3' UTR-STAUFEN ribonucleoprotein particles.

The formation of the anterior pattern of the Drosophila embryo is dependent on the localization of the mRNA of the morphogen Bicoid (bcd) to the anterior pole of the egg cell. Staufen protein (STAU) is required in a late step of the localization to anchor the bcd mRNA in the anterior cytoplasm. We have shown previously that endogenous STAU associates specifically with injected bcd mRNA 3'-untranslated region (UTR), resulting in the formation of characteristic RNA-protein particles that are transported along microtubules of the mitotic spindles in a directed manner. The regions recognized by STAU in this in vivo assay are predicted to form three stem-loop structures involving large double-stranded stretches. Here, we show that the STAU interaction requires a double-stranded conformation of the stems within the RNA localization signal. In addition, base pairing between two single-stranded loops plays a major role in particle formation. This loop-loop interaction is intermolecular, not intramolecular; thus dimers or multimers of the RNA localization signal must be associated with STAU in these particles. The bcd mRNA 3' UTR can also dimerize in vitro in the absence of STAU. Thus, in addition to RNA-protein interactions, RNA-RNA interaction might be involved in the formation of ribonucleoprotein particles for transport and localization.

Animals↗
PubMed1997

Left-right pattern of cardiac BMP4 may drive asymmetry of the heart in zebrafish.

The first evident break in left-right symmetry of the primitive zebrafish heart tube is the shift in pattern of BMP4 expression from radially symmetric to left-predominant. The midline heart tube then 'jogs' to the left and subsequently loops to the right. We examined 279 mutations, affecting more than 200 genes, and found 21 mutations that perturb this process. Some cause BMP4 to remain radially symmetric. Others randomize the asymmetric BMP4 pattern. Retention of BMP4 symmetry is associated with failure to jog: right-predominance of the BMP4 pattern is associated with reversal of the direction of jogging and looping. Raising BMP4 diffusely throughout the heart, via sonic hedgehog injection, or the blocking of its action by injection of a dominant negative BMP4 receptor, prevent directional jogging or looping. The genes crucial to directing cardiac asymmetry include a subset of those needed for patterning the dorsoventral axis and for notochord and ventral spinal cord development. Thus, the pattern of cardiac BMP4 appears to be in the pathway by which the heart interprets lateralizing signals from the midline.

Animals↗
PubMed1996

A gradient of cytoplasmic Cactus degradation establishes the nuclear localization gradient of the dorsal morphogen in Drosophila.

Dorsoventral axis formation in the Drosophila embryo is established by a signal transduction pathway that comprises the products of at least 12 maternal genes. Two of these genes, dorsal and cactus, show homology to the mammalian transcription factor NF-kappa B and its inhibitor I kappa B, respectively. As in the case for I kappa B and NF-kappa B, Cactus inhibits Dorsal by retaining it in the cytoplasm. In response to the signal produced and transmitted by the products of the other genes, Dorsal translocates to the nucleus preferentially on the ventral side of the embryo. Here, we show that Cactus forms a cytoplasmic concentration gradient inversely correlated to the nuclear translocation gradient of Dorsal. Deletions of the N-terminus and C-terminus of Cactus reveal that two modes of degradation control cactus activity: signal-induced degradation and signal-independent degradation, respectively. Genetic evidence indicates that degradation of Cactus is required, but not sufficient to translocates Dorsal completely into the nucleus.

Animals↗
PubMed1996

Fishing for genes controlling development.

In recent years, the zebrafish has become a popular system for studying vertebrate development. Large scale mutant searches have led to the identification of >400 genes with unique functions during embryonic and larval development. A number of these genes play important roles in well studied processes, such as dorsoventral patterning of the early embryo, notochord formation and signaling, somitogenesis and neural specification. Other newly identified genes offer opportunities to investigate less well understood processes, including locomotion behavior, organogenesis, neural crest development and axonal pathfinding.

Animals↗
PubMed1996

The identification of genes with unique and essential functions in the development of the zebrafish, Danio rerio.

In a large-scale screen, we isolated mutants displaying a specific visible phenotype in embryos or early larvae of the zebrafish, Danio rerio. Males were mutagenized with ethylnitrosourea (ENU) and F2 families of single pair matings between sibling F1 fish, heterozygous for a mutagenized genome, were raised. Egg lays were obtained from several crosses between F2 siblings, resulting in scoring of 3857 mutagenized genomes. F3 progeny were scored at the second, third and sixth day of development, using a stereomicroscope. In a subsequent screen, fixed embryos were analyzed for correct retinotectal projection. A total of 4264 mutants were identified. Two thirds of the mutants displaying rather general abnormalities were eventually discarded. We kept and characterized 1163 mutants. In complementation crosses performed between mutants with similar phenotypes, 894 mutants have been assigned to 372 genes. The average allele frequency is 2.4. We identified genes involved in early development, notochord, brain, spinal cord, somites, muscles, heart, circulation, blood, skin, fin, eye, otic vesicle, jaw and branchial arches, pigment pattern, pigment formation, gut, liver, motility and touch response. Our collection contains alleles of almost all previously described zebrafish mutants. From the allele frequencies and other considerations we estimate that the 372 genes defined by the mutants probably represent more than half of all genes that could have been discovered using the criteria of our screen. Here we give an overview of the spectrum of mutant phenotypes obtained, and discuss the limits and the potentials of a genetic saturation screen in the zebrafish.

Animals↗
PubMed1996

Mutations affecting the formation of the notochord in the zebrafish, Danio rerio.

In a large scale screen for mutants with defects in the embryonic development of the zebrafish we identified mutations in four genes,floating head (flh), momo (mom), no tail (ntl), and doc, that are required for early notochord formation. Mutations in flh and ntl have been described previously, while mom and doc are newly identified genes. Mutant mom embryos lack a notochord in the trunk, and trunk somites from the right and left side of the embryo fuse underneath the neural tube. In this respect mom appears similar to flh. In contrast, notochord precursor cells are present in both ntl and doc embryos. In order to gain a greater understanding of the phenotypes, we have analysed the expression of several axial mesoderm markers in mutant embryos of all four genes. In flh and mom, Ntl expression is normal in the germ ring and tailbud, while the expression of Ntl and other notochord markers in the axial mesodermal region is disrupted. Ntl expression is normal in doc embryos until early somitic stages, when there is a reduction in expression which is first seen in anterior regions of the embryo. This suggests a function for doc in the maintenance of ntl expression. Other notochord markers such as twist, sonic hedgehog and axial are not expressed in the axial mesoderm of ntl embryos, their expression parallels the expression of ntl in the axial mesoderm of mutant doc, flh and mom embryos, indicating that ntl is required for the expression of these markers. The role of doc in the expression of the notochord markers appears indirect via ntl. Floor plate formation is disrupted in most regions in flh and mom mutant embryos but is present in mutant ntl and doc embryos. In mutant embryos with strong ntl alleles the band of cells expressing floor plate markers is broadened. A similar broadening is also observed in the axial mesoderm underlying the floor plate of ntl embryos, suggesting a direct involvement of the notochord precursor cells in floor plate induction. Mutations in all of these four genes result in embryos lacking a horizontal myoseptum and muscle pioneer cells, both of which are thought to be induced by the notochord. These somite defects can be traced back to an impairment of the specification of the adaxial cells during early stages of development. Transplantation of wild-type cells into mutant doc embryos reveals that wild-type notochord cells are sufficient to induce horizontal myoseptum formation in the flanking mutant tissue. Thus doc, like flh and ntl, acts cell autonomously in the notochord. In addition to the four mutants with defects in early notochord formation, we have isolated 84 mutants, defining at least 15 genes, with defects in later stages of notochord development. These are listed in an appendix to this study.

Animals↗
PubMed1996

Mutations affecting development of the midline and general body shape during zebrafish embryogenesis.

Tissues of the dorsal midline of vertebrate embryos, such as notochord and floor plate, have been implicated in inductive interactions that pattern the neural tube and somites. In our screen for embryonic visible mutations in the zebrafish we found 113 mutations in more than 27 genes with altered body shape, often with additional defects in CNS development. We concentrated on a subgroup of mutations in ten genes (the midline-group) that cause defective development of the floor plate. By using floor plate markers, such as the signaling molecule sonic hedgehog, we show that the schmalspur (sur) gene is needed for early floor plate development, similar to one-eyed-pinhead (oep) and the previously described cyclops (cyc) gene. In contrast to oep and cyc, sur embryos show deletions of ventral CNS tissue restricted to the mid- and hindbrain, whereas the forebrain appears largely unaffected. In the underlying mesendodermal tissue of the head, sur is needed only for development of the posterior prechordal plate, whereas oep and cyc are required for both anterior and posterior prechordal plate development. Our analysis of sur mutants suggests that defects within the posterior prechordal plate may cause aberrant development of ventral CNS structures in the mid- and hindbrain. Later development of the floor plate is affected in mutant chameleon, you-too, sonic-you, iguana, detour, schmalhans and monorail embryos; these mutants often show additional defects in tissues that are known to depend on signals from notochord and floor plate. For example, sur, con and yot mutants show reduction of motor neurons; median deletions of brain tissue are seen in sur, con and yot embryos; and cyc, con, yot, igu and dtr mutants often show no or abnormal formation of the optic chiasm. We also find fusions of the ventral neurocranium for all midline mutants tested, which may reveal a hitherto unrecognized function of the midline in influencing differentiation of neural crest cells at their destination. As a working hypothesis, we propose that midline-group genes may act to maintain proper structure and inductive function of zebrafish midline tissues.

Animals↗
PubMed1996

Mutations affecting morphogenesis during gastrulation and tail formation in the zebrafish, Danio rerio.

We have identified several genes that are required for various morphogenetic processes during gastrulation and tail formation. Two genes are required in the anterior region of the body axis: one eyed pinhead (oep) and dirty nose (dns).oep mutant embryos are defective in prechordal plate formation and the specification of anterior and ventral structures of the central nervous system. In dns mutants, cells of the prechordal plate, such as the prospective hatching gland cells, fail to specify. Two genes are required for convergence and extension movements. In mutant trilobite embryos, extension movements on the dorsal side of the embryo are affected, whereas in the formerly described spadetail mutants, for which two new alleles have been isolated, convergent movements of ventrolateral cells to the dorsal side are blocked. Two genes are required for the development of the posterior end of the body axis. In pipetail mutants, the tailbud fails to move ventrally on the yolk sac after germ ring closure, and the tip of the tail fails to detach from the yolk tube. Mutants in kugelig (kgg) do not form the yolk tube at the posterior side of the yolk sac.

Animals↗
PubMed1996

Mutations affecting somite formation and patterning in the zebrafish, Danio rerio.

Somitogenesis is the basis of segmentation of the mesoderm in the trunk and tail of vertebrate embryos. Two groups of mutants with defects in this patterning process have been isolated in our screen for zygotic mutations affecting the embryonic development of the zebrafish (Danio rerio). In mutants of the first group, boundaries between individual somites are invisible early on, although the paraxial mesoderm is present. Later, irregular boundaries between somites are present. Mutations in fused somites (fss) and beamter (bea) affect all somites, whereas mutations in deadly seven (des), after eight (aei) and white tail (wit) only affect the more posterior somites. Mutants of all genes but wit are homozygous viable and fertile. Skeletal stainings and the expression pattern of myoD and snail1 suggest that anteroposterior patterning within individual somites is abnormal. In the second group of mutants, formation of the horizontal myoseptum, which separates the dorsal and ventral part of the myotome, is reduced. Six genes have been defined in this group (you-type genes). you-too mutants show the most severe phenotype; in these the adaxial cells, muscle pioneers and the primary motoneurons are affected, in addition to the horizontal myoseptum. The horizontal myoseptum is also missing in mutants that lack a notochord. The similarity of the somite phenotype in mutants lacking the notochord and in the you-type mutants suggests that the genes mutated in these two groups are involved in a signaling pathway from the notochord, important for patterning of the somites.

Animals↗
PubMed1996

Mutations in zebrafish genes affecting the formation of the boundary between midbrain and hindbrain.

Mutations in two genes affect the formation of the boundary between midbrain and hindbrain (MHB): no isthmus (noi) and acerebellar (ace). noi mutant embryos lack the MHB constriction, the cerebellum and optic tectum, as well as the pronephric duct. Analysis of noi mutant embryos with neuron-specific antibodies shows that the MHB region and the dorsal and ventral midbrain are absent or abnormal, but that the rostral hindbrain is unaffected with the exception of the cerebellum. Using markers that are expressed during its formation (eng, wnt1 and pax-b), we find that the MHB region is already misspecified in noi mutant embryos during late gastrulation. The tectum is initially present and later degenerates. The defect in ace mutant embryos is more restricted: MHB and cerebellum are absent, but a tectum is formed. Molecular organisation of the tectum and tegmentum is disturbed, however, since eng, wnt1 and pax-b marker gene expression is not maintained. We propose that noi and ace are required for development of the MHB region and of the adjacent mid- and hindbrain, which are thought to be patterned by the MHB region. Presence of pax-b RNA, and absence of pax-b protein, together with the observation of genetic linkage and the occurrence of a point mutation, show that noi mutations are located in the pax-b gene. pax-b is a vertebrate orthologue of the Drosophila gene paired, which is involved in a pathway of cellular interactions at the posterior compartment boundary in Drosophila. Our results confirm and extend a previous report, and show that at least one member of this conserved signalling pathway is required for formation of the boundary between midbrain and hindbrain in the zebrafish.

Animals↗