Biomedical subjects

H M Maischein

Publications and source records attributed to H M Maischein.

4 recordsLinked to original sources

PubMed1998

Function of zebrafish beta-catenin and TCF-3 in dorsoventral patterning.

We report the molecular cloning and expression of the zebrafish tcf-3 homologue and study its function and that of zebrafish betacat in dorsoventral patterning. Overexpression of mutant zTcf-3 products and Cadherin leads to a reduction in the expression of the dorsal-specific genes goosecoid and chording at the blastula stages, indicating a conserved role for betacat and tcf-3 in zebrafish dorsal axis induction. Later during gastrulation, overexpression of these same products leads to the ectopic expression of dorsal-specific genes in the marginal zone and the induction of ectopic axes, suggesting an additional role for betacat and Tcf-3 at these later stages in the repression of dorsal fates.

Amino Acid Sequence↗

PubMed1996

The zebrafish epiboly mutants.

Epiboly, the enveloping of the yolk cell by the blastoderm, is the first zebrafish morphogenetic movement. We isolated four mutations that affect epiboly: half baked, avalanche, lawine and weg. Homozygous mutant embryos arrest the vegetal progress of the deep cells of the blastoderm; only the yolk syncytial layer of the yolk cell and the enveloping layer of the blastoderm reach the vegetal pole of the embryo. The mutations half baked, avalanche and lawine produce a novel dominant effect, termed a zygotic-maternal dominant effect: heterozygous embryos produced from heterozygous females slow down epiboly and accumulate detached cells over the neural tube; a small fraction of these mutant individuals are viable. Heterozygous embryos produced from heterozygous males crossed to homozygous wild-type females complete epiboly normally and are completely viable. Additionally, embryos heterozygous for half baked have an enlarged hatching gland, a partial dominant phenotype. The phenotypes of these mutants demonstrate that, for the spreading of cells during epiboly, the movement of the deep cells of the blastoderm require the function of genes that are not necessary for the movement of the enveloping layer or the yolk cell. Furthermore, the dominant zygotic-maternal effect phenotypes illustrate the maternal and zygotic interplay of genes that orchestrate the early cell movements of the zebrafish.

Animals↗

PubMed1996

The zebrafish early arrest mutants.

This report describes mutants of the zebrafish having phenotypes causing a general arrest in early morphogenesis. These mutants identify a group of loci making up about 20% of the loci identified by mutants with visible morphological phenotypes within the first day of development. There are 12 Class I mutants, which fall into 5 complementation groups and have cells that lyse before morphological defects are observed. Mutants at three loci, speed bump, ogre and zombie, display abnormal nuclei. The 8 Class II mutants, which fall into 6 complementation groups, arrest development before cell lysis is observed. These mutants seemingly stop development in the late segmentation stages, and maintain a body shape similar to a 20 hour embryo. Mutations in speed bump, ogre, zombie, specter, poltergeist and troll were tested for cell lethality by transplanting mutant cells into wild-type hosts. With poltergeist, transplanted mutant cells all survive. The remainder of the mutants tested were autonomously but conditionally lethal: mutant cells, most of which lyse, sometimes survive to become notochord, muscles, or, in rare cases, large neurons, all cell types which become postmitotic in the gastrula. Some of the genes of the early arrest group may be necessary for progression though the cell cycle; if so, the survival of early differentiating cells may be based on having their terminal mitosis before the zygotic requirement for these genes.

Animals↗

PubMedDate not supplied

A mutation in the zebrafish maternal-effect gene nebel affects furrow formation and vasa RNA localization.

BACKGROUND: In many animals, embryonic patterning depends on a careful interplay between cell division and the segregation of localized cellular components. Both of these processes in turn rely on cytoskeletal elements and motor proteins. A type of localized cellular component found in most animals is the germ plasm, a specialized region of cytoplasm that specifies the germ-cell fate. The gene vasa has been shown in Drosophila to encode an essential component of the germ plasm and is thought to have a similar function in other organisms. In the zebrafish embryo, the vasa RNA is localized to the furrows of the early cellular divisions. RESULTS: We identified the gene nebel in a pilot screen for zebrafish maternal-effect mutations. Embryos from females homozygous for a mutation in nebel exhibit defects in cell adhesion. Our analysis provides genetic evidence for a function of the microtubule array that normally develops at the furrow in the deposition of adhesive membrane at the cleavage plane. In addition, nebel mutant embryos show defects in the early localization of vasa RNA. The vasa RNA localization phenotype could be mimicked with microtubule-inhibiting drugs, and confocal microscopy suggests an interaction between microtubules and vasa-RNA-containing aggregates. CONCLUSIONS: Our data support two functions for the microtubule reorganization at the furrow, one for the exocytosis of adhesive membrane, and another for the translocation of vasa RNA along the forming furrow.

Animals↗