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H Schnabel

Publications and source records attributed to H Schnabel.

At least 19 recordsLinked to original sources
PubMed2000

CYK-4: A Rho family gtpase activating protein (GAP) required for central spindle formation and cytokinesis.

During cytokinesis of animal cells, the mitotic spindle plays at least two roles. Initially, the spindle positions the contractile ring. Subsequently, the central spindle, which is composed of microtubule bundles that form during anaphase, promotes a late step in cytokinesis. How the central spindle assembles and functions in cytokinesis is poorly understood. The cyk-4 gene has been identified by genetic analysis in Caenorhabditis elegans. Embryos from cyk-4(t1689ts) mutant hermaphrodites initiate, but fail to complete, cytokinesis. These embryos also fail to assemble the central spindle. We show that the cyk-4 gene encodes a GTPase activating protein (GAP) for Rho family GTPases. CYK-4 activates GTP hydrolysis by RhoA, Rac1, and Cdc42 in vitro. RNA-mediated interference of RhoA, Rac1, and Cdc42 indicates that only RhoA is essential for cytokinesis and, thus, RhoA is the likely target of CYK-4 GAP activity for cytokinesis. CYK-4 and a CYK-4:GFP fusion protein localize to the central spindle and persist at cell division remnants. CYK-4 localization is dependent on the kinesin-like protein ZEN-4/CeMKLP1 and vice versa. These data suggest that CYK-4 and ZEN-4/CeMKLP1 cooperate in central spindle assembly. Central spindle localization of CYK-4 could accelerate GTP hydrolysis by RhoA, thereby allowing contractile ring disassembly and completion of cytokinesis.

Animals↗
PubMed2000

OOC-3, a novel putative transmembrane protein required for establishment of cortical domains and spindle orientation in the P(1) blastomere of C. elegans embryos.

Asymmetric cell divisions require the establishment of an axis of polarity, which is subsequently communicated to downstream events. During the asymmetric cell division of the P(1) blastomere in C. elegans, establishment of polarity depends on the establishment of anterior and posterior cortical domains, defined by the localization of the PAR proteins, followed by the orientation of the mitotic spindle along the previously established axis of polarity. To identify genes required for these events, we have screened a collection of maternal-effect lethal mutations on chromosome II of C. elegans. We have identified a mutation in one gene, ooc-3, with mis-oriented division axes at the two-cell stage. Here we describe the phenotypic and molecular characterization of ooc-3. ooc-3 is required for the correct localization of PAR-2 and PAR-3 cortical domains after the first cell division. OOC-3 is a novel putative transmembrane protein, which localizes to a reticular membrane compartment, probably the endoplasmic reticulum, that spans the whole cytoplasm and is enriched on the nuclear envelope and cell-cell boundaries. Our results show that ooc-3 is required to form the cortical domains essential for polarity after cell division.

Amino Acid Sequence↗
PubMed1999

Ballistic transformation of Caenorhabditis elegans.

A novel method to transform the nematode Caenorhabditis elegans is described. DNA coprecipitated with gold particles is shot at worms by means of a helium beam. Transformed worms are either identified by a dominant visible marker or selected by a conditional lethal system.

Animals↗
PubMed1999

Dissection of cell division processes in the one cell stage Caenorhabditis elegans embryo by mutational analysis.

To identify novel components required for cell division processes in complex eukaryotes, we have undertaken an extensive mutational analysis in the one cell stage Caenorhabditis elegans embryo. The large size and optical properties of this cell permit observation of cell division processes with great detail in live specimens by simple differential interference contrast (DIC) microscopy. We have screened an extensive collection of maternal-effect embryonic lethal mutations on chromosome III with time-lapse DIC video microscopy. Using this assay, we have identified 48 mutations in 34 loci which are required for specific cell division processes in the one cell stage embryo. We show that mutations fall into distinct phenotypic classes which correspond, among others, to the processes of pronuclear migration, rotation of centrosomes and associated pronuclei, spindle assembly, chromosome segregation, anaphase spindle positioning, and cytokinesis. We have further analyzed pronuclear migration mutants by indirect immunofluorescence microscopy using antibodies against tubulin and ZYG-9, a centrosomal marker. This analysis revealed that two pronuclear migration loci are required for generating normal microtubule arrays and four for centrosome separation. All 34 loci have been mapped by deficiencies to distinct regions of chromosome III, thus paving the way for their rapid molecular characterization. Our work contributes to establishing the one cell stage C. elegans embryo as a powerful metazoan model system for dissecting cell division processes.

Animals↗
PubMed1999

Complexity of developmental control: analysis of embryonic cell lineage specification in Caenorhabditis elegans using pes-1 as an early marker.

In the early Caenorhabditis elegans embryo five somatic founder cells are born during the first cleavages. The first of these founder cells, named AB, gives rise to 389 of the 558 nuclei present in the hatching larva. Very few genes directly involved in the specification of the AB lineage have been identified so far. Here we describe a screen of a large collection of maternal-effect embryonic lethal mutations for their effect on the early expression of a pes-1::lacZ fusion gene. This fusion gene is expressed in a characteristic pattern in 14 of the 32 AB descendants present shortly after the initiation of gastrulation. Of the 37 mutations in 36 genes suspected to be required specifically during development, 12 alter the expression of the pes-1::lacZ marker construct. The gene expression pattern alterations are of four types: reduction of expression, variable expression, ectopic expression in addition to the normal pattern, and reduction of the normal pattern together with ectopic expression. We estimate that approximately 100 maternal functions are required to establish the pes-1 expression pattern in the early embryo.

Animals↗
PubMed1998

cyk-1: a C. elegans FH gene required for a late step in embryonic cytokinesis.

A maternally expressed Caenorhabditis elegans gene called cyk-1 is required for polar body extrusion during meiosis and for a late step in cytokinesis during embryonic mitosis. Other microfilament- and microtubule-dependent processes appear normal in cyk-1 mutant embryos, indicating that cyk-1 regulates a specific subset of cytoskeletal functions. Because cytokinesis initiates normally and cleavage furrows ingress extensively in cyk-1 mutant embryos, we propose that the wild-type cyk-1 gene is required for a late step in cytokinesis. Cleavage furrows regress after completion of mitosis in cyk-1 mutants, leaving multiple nuclei in a single cell. Positional cloning and sequence analysis of the cyk-1 gene reveal that it encodes an FH protein, a newly defined family of proteins that appear to interact with the cytoskeleton during cytokinesis and in the regulation of cell polarity. Consistent with cyk-1 function being required for a late step in embryonic cytokinesis, we show that the CYK-1 protein co-localizes with actin microfilaments as a ring at the leading edge of the cleavage furrow, but only after extensive furrow ingression. We discuss our findings in the context of other studies suggesting that FH genes in yeast and insects function early in cytokinesis to assemble a cleavage furrow.

Actin Cytoskeleton↗
PubMed1998

Serine hydroxymethyltransferase is maternally essential in Caenorhabditis elegans.

The mel-32 gene in the free living soil nematode Caenorhabditis elegans encodes a serine hydroxymethyltransferase (SHMT) isoform. Seventeen ethylmethanesulfonate (EMS)-induced mutant alleles of mel-32(SHMT) have been generated, each of which causes a recessive maternal effect lethal phenotype. Animals homozygous for the SHMT mutations have no observable mutant phenotype, but their offspring display an embryonic lethal phenotype. The Mel-32 phenotype has been rescued with a transgenic array containing only mel-32(SHMT) genomic DNA. Heteroduplex analysis of the 17 alleles allowed 14 of the mutations to be positioned to small regions. Subsequent sequence analysis has shown that 16 of the alleles alter highly conserved amino acids, while one allele introduces a stop codon that truncates two thirds of the predicted protein. mel-32(SHMT) has a 55-60% identity at the amino acid level with both isoforms of SHMT found in yeast and humans and a 50% identity with the Escherichia coli isoform. The C. elegans mel-32 mutation represents the first case where SHMT has been shown to be an essential gene.

Amino Acid Sequence↗
PubMed1997

Binary specification of the embryonic lineage in Caenorhabditis elegans.

In Caenorhabditis elegans, the early embryo contains five somatic founder cells (known as AB, MS, E, C and D) which give rise to very different lineages. Two simply produce twenty intestinal (E) or muscle (D) cells each, whereas the remainder produce a total of 518 cells which collectively contribute in a complex pattern to a variety of tissues. A central problem in embryonic development is to understand how the developmental potential of blastomeres is restricted to permit the terminal expression of such complex differentiation patterns. Here we identify a gene, lit-1, that appears to play a central role in controlling the asymmetry of cell division during embryogenesis in C. elegans. Mutants in lit-1 suggest that its product controls up to six consecutive binary switches which cause one of the two equivalent cells produced at each cleavage to assume a posterior fate. Most blastomere identities in C. elegans may therefore stem from a process of stepwise binary diversification.

Animals↗
PubMed1997

Assessing normal embryogenesis in Caenorhabditis elegans using a 4D microscope: variability of development and regional specification.

Caenorhabditis elegans is renowned for its invariant embryogenesis. This pattern of development is in apparent contrast to other organisms from Drosophila to higher vertebrates. With the aid of a 4D microscope system (multifocal, time-lapse video recording system) which permits the extensive documentation and analysis of cell divisions, cell positions, and migrations in single embryos we have analyzed normal embryogenesis of C. elegans. The instrumentation reveals a naturally occurring variability in cell division timing, cell positioning, and cell-cell contacts which could not have been detected by the direct observation used earlier (Sulston et al., 1983, Dev. Biol. 100, 64-119). Embryos are very flexible and produce an essentially invariant premorphogenetic stage from variable earlier stages. An analysis of the distribution of the descendants of the early founder blastomeres at the premorphogenetic stage shows that these establish discrete regions in the embryo, a process involving a considerable amount of cell movement, which again varies in different embryos. Only cell fate assignment remains invariant. However, as shown earlier, this is not due to an autonomous invariant specification of cell fates but due to the fact that cell-cell interactions occur very early when the topology of blastomeres in the embryo is still sufficiently precise to ensure reproducible patterns of inductions. A new concept that founder blastomeres produce embryonic regions in the embryo can explain the striking complexity of the lineage per se and also the complicated asymmetric lineage patterns by which the bilateral symmetry of the embryo is established. Many cells, including bilateral homologs, were apparently chosen for a specific fate solely by their position in the embryo, irrespectively of the lineage descent by which the cells are created. We postulate that the production of regions by cell-cell interactions is the pivotal principle guiding the embryogenesis of C. elegans and that the embryogenesis of the worm follows the same basic principles as embryogenesis in other organisms.

Animals↗
PubMed1996

mex-1 and the general partitioning of cell fate in the early C. elegans embryo.

It is thought that at least some of the initial specification of the five somatic founder cells of the C. elegans embryo occurs cell-autonomously through the segregation of factors during cell divisions. It has been suggested that in embryos from mothers homozygous for mutations in the maternal-effect gene mex-1, four blastomeres of the 8-cell embryo adopt the fate of the MS blastomere. It was proposed that mex-1 functions to localise or regulate factors that determine the fate of this blastomere. Here, a detailed cell lineage analysis of 9 mex-1 mutants reveals that the fates of all somatic founder cells are affected by mutations in this gene. We propose that mex-1, like the par genes, is involved in establishing the initial polarity of the embryo.

Alleles↗
PubMed1994

Genesis of an organ: molecular analysis of the pha-1 gene.

The organisation of organ formation is still an unsolved problem. Mutations in the zygotic lethal gene pha-1 affect a late step during organ development in the nematode C. elegans. In mutant embryos all tissues in the pharynx fail to undergo terminal differentiation and morphogenesis. The expression of an early differentiation marker in pharyngeal muscle precursors is not impaired in mutant embryos, which suggests that pharynx cells still acquire their identity. Therefore the gene defines an organ-specific terminal differentiation function. We cloned and sequenced the pha-1 gene and found that the deduced protein sequence contains features characteristic of the bZIP family of transcription factors. During embryogenesis a transgenic pha-1 reporter construct is expressed transiently in all pharynx precursor cells at the time when these cells become restricted to form the pharynx organ. A mosaic analysis of the requirement of pha-1 activity during pharynx formation is consistent with the notion that pha-1 acts cell-autonomously in all cells of the pharynx primordium. The data suggest that pha-1 initiates and coordinates programs required for cytodifferentiation and morphogenesis in all cell types of the entire organ on the transcriptional level. We propose that organs are independent developmental units whose identity is reflected on the gene regulatory level.

Amino Acid Sequence↗
PubMed1991

Suppressors of the organ-specific differentiation gene pha-1 of Caenorhabditis elegans.

The embryonic lethal gene pha-1 of the nematode Caenorhabditis elegans is required for late differentiation and morphogenesis of the pharynx in the developing embryo. Revertants of two temperature-sensitive alleles of pha-1 were isolated with the aim of obtaining mutations in genes that interact with pha-1. By various methods of mutagenesis, chemical, X-ray, transposon, or by spontaneous reversion, 220 recessive revertants were obtained, defining three complementation groups. The largest, sup-35 on linkage group (LG) III, maps close to but is separable from pha-1. This suppressor can exert its effect either maternally or zygotically to allow survival of pha-1(ts) embryos. The other two, sup-36 and sup-37, are required zygotically and map on LGIV and LGV, respectively. We have not noted a phenotype distinguishing any of the suppressors from wild type except for suppression of pha-1. That suppression is the null phenotype of at least sup-35 is indicated by the high frequency of mutation and by the fact that heterozygotes carrying sup-35 and a deficiency spanning the locus are also able to suppress. Five spontaneous mutations in sup-35 were found to be associated with recombination.

Animals↗
PubMed1990

Early determination in the C. elegans embryo: a gene, cib-1, required to specify a set of stem-cell-like blastomeres.

The early somatic blastomeres founding the tissues in the C. elegans embryo are derived in a stem-cell-like lineage from the P cells. We have isolated maternal effect lethal mutations defining the gene cib-1 in which the P cells, P1-P3, skip a cell cycle and acquire the fates of only their somatic daughters. Therefore, the cib-1 gene is required for the specification of the stem-cell-like fate of these cells. The analysis of the development of these mutants suggests that the clock controlling the cell cycles in the early embryo is directly coupled to the fate of a cell and that there must be another developmental clock that activates the determinative inventory for the early decision-making.

Alleles↗
PubMed1990

[Distemper as the cause of death in badgers in Austria].

A canine distemper virus infection of badgers in a hunting range in Austria is described. A badger which was shot after showing symptoms of rabies infection and one which was found dead were examined by gross pathology and parasitological, histological, bacteriological and virological methods. The examination for rabies was negative in both cases. The badger which was found dead histologically showed signs of a non purulent panencephalitis, the shot animal showed hyperaemia and oedema of the brain. No cytoplasmatic or nuclear inclusion bodies could be observed. The aetiologic viral diagnosis was achieved by immunofluorescence. Using two canine distemper-specific conjugates a typical granular fluorescence of different strength could be observed in organ sections. The bacterial examination showed in both cases a secondary infection with opportunistic pathogenic bacteria (haem. E. coli and Pseudomonas aeruginosa).

Animals↗
PubMed1987

The glp-1 locus and cellular interactions in early C. elegans embryos.

Interactions between the early blastomeres in a C. elegans embryo are required for the specification of certain cell fates. Blastomeres that produce neurons and skin cells when cultured in isolation are induced to also produce pharyngeal cells in intact embryos. We have identified maternal effect lethal mutations that, on the basis of phenotype and temperature-sensitive period, appear to disrupt this inductive interaction. These mutations are all alleles of glp-1, a gene also involved in the control of germ cell proliferation during postembryonic development of C. elegans.

Alleles↗
PubMed1984

Sequence analysis of the insertion element ISH1.8 and of associated structural changes in the genome of phage PhiH of the archaebacterium Halobacterium halobium.

We have sequenced the insertion element ISH1.8 which can be present in one or two copies in the genome of phage PhiH of Halobacterium halobium. ISH1.8 is 1895 bp long, has no inverted repeat at its ends, and one only of the two copies is flanked by two 5-bp duplications. An 8-bp sequence composed of 4 bp from each end of ISH1.8 is present in both sites lacking the element. This 8-bp sequence could either be a specific insertion sequence or a part of the element that is left behind upon deletion. The plasmid pPhiHL, consisting of the invertible L segment of the phage genome which is, in PhiH2 and PhiH5, flanked by two copies of ISH1.8, contains 112 bp of ISH1.8 and is released from the phage genome by recombination within a direct repeat of 9 bp. This 9-bp sequence (TCCCGCCCT) exists as an inverted repeat in ISH1.8 and therefore as two distinct repeats in phage genomes containing two copies of ISH1.8 in inverted orientation.

Journal Article↗