title: Differential role of Axin RGS domain function in Wnt signaling during anteroposterior patterning and maternal axis formation.
abstract: Axin is a critical component of the β-catenin destruction complex and is also necessary for Wnt signaling initiation at the level of co-receptor activation. Axin contains an RGS domain, which is similar to that of proteins that accelerate the GTPase activity of heterotrimeric Gα/Gna proteins and thereby limit the duration of active G-protein signaling. Although G-proteins are increasingly recognized as essential components of Wnt signaling, it has been unclear whether this domain of Axin might function in G-protein regulation. This study was performed to test the hypothesis that Axin RGS-Gna interactions would be required to attenuate Wnt signaling. We tested these ideas using an axin1 genetic mutant (masterblind) and antisense oligo knockdowns in developing zebrafish and Xenopus embryos. We generated a point mutation that is predicted to reduce Axin-Gna interaction and tested for the ability of the mutant forms to rescue Axin loss-of-function function. This Axin point mutation was deficient in binding to Gna proteins in vitro, and was unable to relocalize to the plasma membrane upon Gna overexpression. We found that the Axin point mutant construct failed to rescue normal anteroposterior neural patterning in masterblind mutant zebrafish, suggesting a requirement for G-protein interactions in this context. We also found that the same mutant was able to rescue deficiencies in maternal axin1 loss-of-function in Xenopus. These data suggest that maternal and zygotic Wnt signaling may differ in the extent of Axin regulation of G-protein signaling. We further report that expression of a membrane-localized Axin construct is sufficient to inhibit Wnt/β-catenin signaling and to promote Axin protein turnover.
authors.affiliation: Interdisciplinary Graduate Program in Genetics, Department of Biology, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Patricia N
authors.initials: PN
authors.lastname: Schneider
authors.forename: Diane C
authors.initials: DC
authors.lastname: Slusarski
authors.forename: Douglas W
authors.initials: DW
authors.lastname: Houston
mesh_terms: D000818:Animals; D060466:Axin Protein / Q000378:metabolism*; D019521:Body Patterning; D051157:Frizzled Receptors / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008954:Models, Biological; D009154:Mutation; D010641:Phenotype; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D051153:Wnt Proteins / Q000378:metabolism*; D014982:Xenopus laevis; D015027:Zebrafish; D051176:beta Catenin / Q000378:metabolism
chemical_list: D060466:Axin Protein; D051157:Frizzled Receptors; D012333:RNA, Messenger; D051153:Wnt Proteins; D051176:beta Catenin; D019204:GTP-Binding Proteins