title: The role of Mixer in patterning the early Xenopus embryo.
abstract: The transcription factor VegT, is required in early Xenopus embryos for the formation of both the mesoderm and endoderm germ layers. Inherited as a maternal mRNA localized only in vegetal cells, VegT activates the transcription of a large number of transcription factors, as well as signaling ligands that induce cells in the vegetal mass to form endoderm, and the marginal zone to form mesoderm. It is important now to understand the extent to which transcription factors downstream of VegT play individual, or overlapping, roles in the specification and patterning of the endoderm and mesoderm. In addition, it is important to understand the mechanism that specifies the boundary between endoderm and mesoderm. One of the downstream targets of VegT, the homeodomain protein Mixer, is expressed at high levels at the mesoderm/endoderm boundary at the late blastula stage. We therefore examined its functions by blocking its translation using morpholino oligos. In Mixer-depleted embryos, the expression of many signaling ligands and transcription factors was affected. In particular, we found that the expression of several genes, including several normally expressed in mesoderm, was upregulated. Functional assays of Mixer-depleted vegetal cells showed that they have increased mesoderm-inducing activity. This demonstrates that Mixer plays an essential role in controlling the amount of mesoderm induction by the vegetal cells.
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Research Foundation, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, USA.
authors.forename: Matt
authors.initials: M
authors.lastname: Kofron
authors.forename: Chris
authors.initials: C
authors.lastname: Wylie
authors.forename: Janet
authors.initials: J
authors.lastname: Heasman
mesh_terms: D000818:Animals; D001483:Base Sequence; D036703:Blastula; D019521:Body Patterning / Q000502:physiology*; D000013:Congenital Abnormalities / Q000235:genetics; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology*; D004707:Endoderm / Q000502:physiology; D005775:Gastrula / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D008648:Mesoderm / Q000502:physiology; D008969:Molecular Sequence Data; D009843:Oligoribonucleotides / Q000737:chemistry; D009924:Organ Culture Techniques; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D029867:Xenopus Proteins / Q000235:genetics*; D014982:Xenopus laevis / Q000196:embryology*; D015053:Zygote / Q000502:physiology
chemical_list: D018398:Homeodomain Proteins; D009843:Oligoribonucleotides; D012333:RNA, Messenger; D014157:Transcription Factors; D029867:Xenopus Proteins; C405705:mixer protein, Xenopus