Publications in 2004

Koch, R., Rauch, G.J., Humphray, S., Geisler, T.R. and Plasterk, R.H.A. (2004). Bacterial artificial chromosome (BAC) clones and the current clone map of the zebrafish genome. Methods Cell Biol 77, 295-304.

Lee, J.S., von der Hardt, S., Rusch, M.A., Stringer, S.E., Stickney, H.L., Talbot, W.S., Geisler, R., Nüsslein-Volhard, C., Selleck, S.B., Chien, C.B. and Roehl, H. (2004). Axon Sorting in the Optic Tract Requires HSPG Synthesis by ext2 (dackel) and extl3 (boxer). Neuron 16, 947-60.

Retinal ganglion cell (RGC) axons are topographically ordered in the optic tract according to their retinal origin. In zebrafish dackel (dak) and boxer (box) mutants, some dorsal RGC axons missort in the optic tract but innervate the tectum topographically. Molecular cloning reveals that dak and box encode ext2 and extl3, glycosyltransferases implicated in heparan sulfate (HS) biosynthesis. Both genes are required for HS synthesis, as shown by biochemical and immunohistochemical analysis, and are expressed maternally and then ubiquitously, likely playing permissive roles. Missorting in box can be rescued by overexpression of extl3. dak;box double mutants show synthetic pathfinding phenotypes that phenocopy robo2 mutants, suggesting that Robo2 function requires HS in vivo; however, tract sorting does not require Robo function, since it is normal in robo2 null mutants. This genetic evidence that heparan sulfate proteoglycan function is required for optic tract sorting provides clues to begin understanding the underlying molecular mechanisms.

Söllner, C., Schwarz, H., Geisler. R. and Nicolson, T. (2004). Mutated otopetrin 1 affects the genesis of otoliths and the localization of Starmaker in zebrafish. Dev Genes Evol 214, 582 - 90.

Otoliths in bony fishes and otoconia in mammals are composite crystals consisting of calcium carbonate and proteins. These biominerals are part of the gravity and linear acceleration detection system of the inner ear. Mutations in otopetrin 1 have been shown to result in lack of otoconia in tilted and mergulhador mutant mice. The molecular function of Otopetrin 1, a novel protein that contains ten predicted transmembrane domains, however, has remained elusive. Here we show that a mutation in the orthologous gene in zebrafish is responsible for the complete absence of otoliths in backstroke mutants. We examined the localization of Starmaker, a secreted protein that is highly abundant in otoliths in backstroke mutants. Starmaker protein accumulated within cells of the otic epithelium, indicating a possible defect in secretion. Our data suggest that Otopetrin 1 in zebrafish may be involved in the protein trafficking of components required for formation of biominerals in the ear.

Gilmour D., Knaut H., Maischein H.-M., Nüsslein-Volhard C. (2004). Towing of sensory axons by their migrating target cells in vivo. Nat Neurosci. 7(5):491-492

Many pathfinding axons must locate target fields that are themselves positioned by active migration. A hypothetical method for ensuring that these migrations are coordinated is towing, whereby the extension of axons is entirely dependent on the migration of their target cells. Here we combine genetics and time-lapse imaging in the zebrafish to show that towing by migrating cells is a bona fide mechanism for guiding pathfinding axons in vivo.

Wolff, C., Roy, S., Lewis, K. E., Schauerte, H., Rauch, J., Kirn, A., Weiler, C., Geisler, R., Haffter, P., Ingham, P. (2004). Iguana encodes a novel zinc-finger protein with coiled-coil domains essential for Hedgehog signal transduction in the zebrafish embryo. Genes Development 13, 1565-1576

Signaling by lipid-modified secreted glycoproteins of the Hedgehog family play fundamental roles during pattern formation in animal development and in humans; dysfunction of Hedgehog pathway components is frequently associated with a variety of congenital abnormalities and cancer. Transcriptional regulation of Hedgehog target genes is mediated by members of the Gli zinc-finger transcription factors. The relative nuclear concentrations of Gli activator (Gli(act)) and repressor (Gli(rep)) forms, together with their nucleocytoplasmic trafficking, appear to be critical determinants for target gene expression. Whereas such stringent controls of Gli activity are critical in ensuring appropriate levels of pathway activation, the mechanisms by which these processes are regulated remain inadequately understood. Here, using genetic analysis, we show that the zebrafish iguana gene product acts downstream of the Smoothened protein to modulate Gli activity in the somites of the developing embryo. Positional cloning reveals that iguana encodes the zebrafish ortholog of Dzip1, a novel zinc-finger/coiled-coil domain protein that we show can shuttle between the cytoplasm and nucleus in a manner correlated with Hedgehog pathway activity.

Nüsslein-Volhard, C. (2004). The Bicoid Morphogen Paper (I). Cell 116, 1 - 9

Luschnig, S., Moussian, B., Krauss, J., Desjeux, I., Perkovic, J., Nüsslein-Volhard, C. (2004). An F1 genetic screen for maternal-effect mutations affecting embryonic pattern formation in Drosophila melanogaster. Genetics 167, 325 - 342

Large-scale screens for female-sterile mutations have revealed genes required maternally for establishment of the body axes in the Drosophila embryo. Although it is likely that the majority of components involved in axis formation have been identified by this approach, certain genes have escaped detection. This may be due to (1) incomplete saturation of the screens for female-sterile mutations and (2) genes with essential functions in zygotic development that mutate to lethality, precluding their identification as female-sterile mutations. To overcome these limitations, we performed a genetic mosaic screen aimed at identifying new maternal genes required for early embryonic patterning, including zygotically required ones. Using the Flp-FRT technique and a visible germline clone marker, we developed a system that allows efficient screening for maternal-effect phenotypes after only one generation of breeding, rather than after the three generations required for classic female-sterile screens. We identified 232 mutants showing various defects in embryonic pattern or morphogenesis. The mutants were ordered into 10 different phenotypic classes. A total of 174 mutants were assigned to 86 complementation groups with two alleles on average. Mutations in 45 complementation groups represent most previously known maternal genes, while 41 complementation groups represent new loci, including several involved in dorsoventral, anterior-posterior, and terminal patterning.

Söllner, C., Rauch, G.-J., Siemens, J., Geisler, R., Schuster, S.C., The Tübingen 2000 Screen Consortium, Müller, U., and Nicolson, T. (2004). Mutations in cadherin 23 affect tip links in zebrafish sensory hair cells. Nature 428, 955-959.

Hair cells have highly organized bundles of apical projections, or stereocilia, that are deflected by sound and movement. Displacement of stereocilia stretches linkages at the tips of stereocilia that are thought to gate mechanosensory channels. To identify the molecular machinery that mediates mechanotransduction in hair cells, zebrafish mutants were identified with defects in balance and hearing. In sputnik mutants, stereociliary bundles are splayed to various degrees, with individuals displaying reduced or absent mechanotransduction. Here we show that the defects in sputnik mutants are caused by mutations in cadherin 23 (cdh23). Mutations in Cdh23 also cause deafness and vestibular defects in mice and humans, and the protein is present in hair bundles. We show that zebrafish Cdh23 protein is concentrated near the tips of hair bundles, and that tip links are absent in homozygous sputnik(tc317e) larvae. Moreover, tip links are absent in larvae carrying weak alleles of cdh23 that affect mechanotransduction but not hair bundle integrity. We conclude that Cdh23 is an essential tip link component required for hair-cell mechanotransduction.

Srinivasan, J., Otto, G.W., Kahlow, U., Geisler, R. and Sommer, R.J. (2004): AppaDB: an AcedB database for the nematode satellite organism Pristionchus pacificus. Nucleic Acids Research Vol.32, Database issue D421-422.

Pristionchus pacificus is a free-living nematode of the Diplogastridae family and was recently developed as a satellite system in evolutionary developmental biology. AppaDB, a P.pacificus database, was created (http://appadb.eb.tuebingen.mpg.de) to integrate the genomic data of P.pacificus, comprising the physical map, genetic linkage map, EST and BAC end sequence and hybridization data. This developing database serves as a repository to search and find any information regarding physical contigs or genetic markers required for mapping of mutants. Additionally, it provides a platform for the Caenorhabditis elegans community to compare nematode genetic data in an evolutionary perspective.