Identification of distinct classes and functional domains of Wnts through expression of wild-type and chimeric proteins in Xenopus embryos.
Wnts are secreted signaling factors which influence cell fate and cell behavior in developing embryos. Overexpression in Xenopus laevis embryos of a Xenopus Wnt, Xwnt-8, leads to a duplication of the embryonic axis. In embryos ventralized by UV irradiation, Xwnt-8 restores expression of the putative transcription factor goosecoid, and rescues normal axis formation. In contrast, overexpression of Xwnt-5A in normal embryos generates defects in dorsoanterior structures, without inducing goosecoid or a secondary axis. To determine whether Xwnt-4 and Xwnt-11 fall into one of these two previously described classes of activity, synthetic mRNAs were introduced into animal caps, normal embryos, and UV-treated embryos. The results indicate that Xwnt-4, Xwnt-5A, and Xwnt-11 are members of a single functional class with activities that are indistinguishable in these assays. To investigate whether distinct regions of Xwnt-8 and Xwnt-5A were sufficient for eliciting the observed effects of overexpression, we generated a series of chimeric Xwnts. RNAs encoding the chimeras were injected into normal and UV-irradiated Xenopus embryos. Analysis of the embryonic phenotypes and goosecoid levels reveals that chimeras composed of carboxy-terminal regions of Xwnt-8 and amino-terminal regions of Xwnt-5A are indistinguishable from the activities of native Xwnt-8 and that are the reciprocal chimeras elicit effects indistinguishable from overexpression of native Xwnt-5A. We conclude that the carboxy-terminal halves of these Xwnts are candidate domains for specifying responses to Xwnt signals.
Du
S J
SJ
Department of Pharmacology, University of Washington School of Medicine, Seattle, USA.
Purcell
S M
SM
Christian
J L
JL
McGrew
L L
LL
Moon
R T
RT
D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D004625:Embryo, Nonmammalian; D005260:Female; D015870:Gene Expression; D008969:Molecular Sequence Data; D010641:Phenotype; D011518:Proto-Oncogene Proteins / Q000145:classification / Q000235:genetics / Q000502:physiology*; D012315:RNA Caps / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction; D014982:Xenopus laevis / Q000196:embryology / Q000235:genetics
D017931:DNA Primers; D011518:Proto-Oncogene Proteins; D012315:RNA Caps; D011993:Recombinant Fusion Proteins