Rhombomere boundaries are Wnt signaling centers that regulate metameric patterning in the zebrafish hindbrain.
The vertebrate hindbrain develops from a series of segments (rhombomeres) distributed along the anteroposterior axis. We are studying the roles of Wnt and Delta-Notch signaling in maintaining rhombomere boundaries as organizing centers in the zebrafish hindbrain. Several wnt genes (wnt1, wnt3a, wnt8b, and wnt10b) show elevated expression at rhombomere boundaries, whereas several delta genes (dlA, dlB, and dlD) are expressed in transverse stripes flanking rhombomere boundaries. Partial disruption of Wnt signaling by knockdown of multiple wnt genes, or the Wnt mediator tcf3b, ablates boundaries and associated cell types. Expression of dlA is chaotic, and cell types associated with rhombomere centers are disorganized. Similar patterning defects are observed in segmentation mutants spiel-ohne-grenzen (spg) and valentino (val), which fail to form rhombomere boundaries due to faulty interactions between adjacent rhombomeres. Stripes of wnt expression are variably disrupted, with corresponding disturbances in metameric patterning. Mutations in dlA or mind bomb (mib) disrupt Delta-Notch signaling and cause a wide range of patterning defects in the hindbrain. Stripes of wnt1 are initially normal but subsequently dissipate, and metameric patterning becomes increasingly disorganized. Driving wnt1 expression using a heat-shock construct partially rescues metameric patterning in mib mutants. Thus, rhombomere boundaries act as Wnt signaling centers required for precise metameric patterning, and Delta signals from flanking cells provide feedback to maintain wnt expression at boundaries. Similar feedback mechanisms operate in the Drosophila wing disc and vertebrate limb bud, suggesting coaptation of a conserved signaling module that spatially organizes cells in complex organ systems.
Riley
Bruce B
BB
Biology Department, Texas A&M University, College Station, Texas 77843-3258, USA. briley@mail.bio.tamu.edu
Chiang
Ming-Yung
MY
Storch
Elly M
EM
Heck
Rebecca
R
Buckles
Gerri R
GR
Lekven
Arne C
AC
D000818:Animals; D019521:Body Patterning; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004628:Embryonic Structures / Q000033:anatomy & histology / Q000502:physiology*; D051542:Hepatocyte Nuclear Factor 3-beta; D017403:In Situ Hybridization; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009024:Morphogenesis; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D051880:Receptors, Notch; D012249:Rhombencephalon / Q000033:anatomy & histology / Q000196:embryology* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D051153:Wnt Proteins; D051155:Wnt1 Protein; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009687:Nuclear Proteins; D051880:Receptors, Notch; D014157:Transcription Factors; D051153:Wnt Proteins; D051155:Wnt1 Protein; D029961:Zebrafish Proteins; C064045:delta protein; D051542:Hepatocyte Nuclear Factor 3-beta