Wnt1 and wnt10b function redundantly at the zebrafish midbrain–hindbrain boundary

Abstract

Wnt signals have been shown to be involved in multiple steps of vertebrate neural patterning, yet the relative contributions of individual Wnts to the process of brain regionalization is poorly understood. Wnt1 has been shown in the mouse to be required for the formation of the midbrain and the anterior hindbrain, but this function of wnt1 has not been explored in other model systems. Further, wnt1 is part of a Wnt cluster conserved in all vertebrates comprising wnt1 and wnt10b, yet the function of wnt10b during embryogenesis has not been explored. Here, we report that in zebrafish wnt10b is expressed in a pattern overlapping extensively with that of wnt1. We have generated a deficiency allele for these closely linked loci and performed morpholino antisense oligo knockdown to show that wnt1 and wnt10b provide partially redundant functions in the formation of the midbrain-hindbrain boundary (MHB). When both loci are deleted, the expression of pax2.1, en2, and her5 is lost in the ventral portion of the MHB beginning at the 8-somite stage. However, wnt1 and wnt10b are not required for the maintenance of fgf8, en3, wnt8b, or wnt3a expression. Embryos homozygous for the wnt1-wnt10b deficiency display a mild MHB phenotype, but are sensitized to reductions in either Pax2.1 or Fgf8; that is, in combination with mutant alleles of either of these loci, the morphological MHB is lost. Thus, wnt1 and wnt10b are required to maintain threshold levels of Pax2.1 and Fgf8 at the MHB.

Rhombomere boundaries are Wnt signaling centers that regulate metameric patterning in the zebrafish hindbrain

“…1D-F) and stripes are maintained through at least 48 hpf (data not shown). Similar patterns of expression are seen for wnt10b and wnt3a (Lekven et al, 2003;Fig. 1I, and data not shown).…”

“…Expression of wnt1 is first detected at 8 hours postfertilization (hpf) (80% epiboly) in the future midbrain-hindbrain border (Lekven et al, 2003). Between 11 and 14 hpf (1-10 somites), expression marks dorsal hindbrain and spinal cord, and by 16 hpf (14 somites), expression shows segmental regions of up-regulation ( Fig.…”

“…Embryos homozygous for a deletion that removes both wnt1 and wnt10b (Df w5 , Lekven et al, 2003) develop with nearly normal expression of dlA and hindbrain morphology ( Fig. 2A, and data not shown).…”

“…The Df(LG23)wnt1 w5 deletion (herein referred to as Df w5 ) was induced by gamma-irradiation and identified in a polymerase chain reactionbased screen for loss of wnt1 (Lekven et al, 2000). Subsequent mapping showed that Df w5 removes 500 kb or less of LG 23, including the closely linked wnt10b locus (Lekven et al, 2003). Reference to mutants in the text indicates homozygous mutants unless otherwise noted.…”

Inhibition of Jagged-mediated Notch signaling disrupts zebrafish biliary development and generates multi-organ defects compatible with an Alagille syndrome phenocopy

“…Partial redundancy of duplicated zebrafish jagged gene function is compatible with overlapping jagged gene expression patterns at early developmental time points and may explain several aspects of the zebrafish jagged morphant phenotypes. Such models of organ-specific gene compensation are compatible with the function of other zebrafish gene families (Dorsky et al, 2003;Henry et al, 2002;Lekven et al, 2003).…”