Zebrafish wnt8 Encodes Two Wnt8 Proteins on a Bicistronic Transcript and Is Required for Mesoderm and Neurectoderm Patterning

Abstract

In vertebrates, wnt8 has been implicated in the early patterning of the mesoderm. To determine directly the embryonic requirements for wnt8, we generated a chromosomal deficiency in zebrafish that removes the bicistronic wnt8 locus. We report that homozygous mutants exhibit pronounced defects in dorso-ventral mesoderm patterning and in the antero-posterior neural pattern. Despite differences in their signaling activities, either coding region of the bicistronic RNA can rescue the deficiency phenotype. Specific interference of wnt8 translation by morpholino antisense oligomers phenocopies the deficiency, and interference with wnt8 translation in ntl and spt mutants produces embryos lacking trunk and tail. These data demonstrate that the zebrafish wnt8 locus is required during gastrulation to pattern both the mesoderm and the neural ectoderm properly.

Development of the zebrafish inner ear

“…Thus, signals that specify positional identity of the ectoderm can be viewed as early determinants of otic competence. From this perspective, it is noteworthy that putative otic inducers Wnt8 and Fgf8 also play early roles in axial specification (Fü rthauer et al, 1997;Lekven et al, 2001). The graded expression of fgf3 during early gastrulation, and the effects of misexpression of fgf3, suggest that it, too, regulates axial development (Phillips et al, 2001;Raible and Brand, 2001).…”

“…These cultures were not able to be maintained long enough to allow for gene transfer and cell selection for targeted gene insertion, but further elaboration of this technology may eventually lead to the ability to target specific genes for disruption as in the mouse. In the mean time, morpholinos provide a reliable method of transient gene "knockdown", and reverse genetics can still be accomplished by screening for randomly induced mutations affecting genes of interest (Appel et al, 1999;Lekven et al, 2001; reviewed in Lekven et al, 2000).…”

Constructing the hindbrain: Insights from the zebrafish

“…Several lines of evidence have implicated wnt signals in the specification of posterior neural fates. Wnt8 is expressed in the lateral germ ring at the onset of gastrulation, and blocking wnt8 function, either genetically, with dominant-negative forms of the protein, or by using antisense "morpholino" oligonucleotides that prevent translation of the cognate mRNA (Nasevicius and Ekker, 2000) causes expansion of forebrain markers and loss of hindbrain markers in zebrafish and Xenopus embryos (McGrew et al, 1997;Lekven et al, 2001;Erter et al, 2001). The presence of a posteriorizing wnt signal in the embryo is also strongly suggested by the observation, in several vertebrate systems, that wnt antagonists are required in the anterior of the embryos to specify forebrain development.…”

Zebrafish peptidoglycan recognition protein SC (zfPGRP-SC) mediates multiple intracellular signaling pathways

“…Zebrafish Wnt-8 is thought to activate b-catenin signaling which is required for regulating gene expression and cell fates [22], and Wnt-11 for eliciting Wnt/Ca 2þ signals that control cell movement, but not in specification of cell fates [23]. The up-regulation of Wnt-8, Wnt-11 and frizzled receptor for Wnt proteins in embryos silenced by zfPGRP-SC indicates that the suppression of zfPGRP-SC may activate both Wnt/b-catenin and Wnt/Ca 2þ signaling.…”