title: The Sox axis, Nodal signaling, and germ layer specification.
abstract: Asymmetries in the egg, established during oogenesis, set the stage for a cascade of intercellular signaling events leading to differential gene expression and subsequent tissue and organ formation. Maternally supplied Sox-type transcription factors have recently emerged as key components in the patterning of the early embryo and the regulation of embryonic stem cell differentiation. In deuterostomes, B1-type Soxs are asymmetrically localized to the future animal/ectodermal region where they act to suppress mesendodermal, and favor neuroectodermal differentiation, while vegetally localized F-type Soxs are involved in mesendodermal differentiation. Here, we review past observations and present new data from studies on the clawed frog Xenopus laevis. Animally localized Sox3 acts to inhibit Nodal (Xnr5 and Xnr6) expression, and induces the expression of genes (Ectodermin, Xema, and Coco) whose products repress Nodal signaling. Vegetally localized Sox7 positively regulates Nodal (Xnr4, Xnr5, and Xnr6) expression, as well as the expression of genes involved in mesodermal (Xmenf, Slug, and Snail) and endodermal (Endodermin and Sox17beta) differentiation. Given the evolutionary strategy of using common regulatory networks, it seems likely that a homologous Sox-Axis is active during embryonic development in many metazoans.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology University of Colorado at Boulder Boulder, CO 80309-0347, USA.
authors.forename: Chi
authors.initials: C
authors.lastname: Zhang
authors.forename: Michael W
authors.initials: MW
authors.lastname: Klymkowsky
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016764:Cell Polarity / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D003907:Dexamethasone / Q000494:pharmacology; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics*; D005855:Germ Layers / Q000196:embryology / Q000378:metabolism*; D006609:High Mobility Group Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D055457:Nodal Protein; D055456:Nodal Signaling Ligands; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000096:biosynthesis; D011965:Receptors, Glucocorticoid / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid / Q000187:drug effects / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055748:SOXB1 Transcription Factors; D055760:SOXF Transcription Factors; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000502:physiology*; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; C526007:NODAL protein, human; D055457:Nodal Protein; D055456:Nodal Signaling Ligands; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D011993:Recombinant Fusion Proteins; C527785:SOX3 protein, human; D055748:SOXB1 Transcription Factors; D055760:SOXF Transcription Factors; C527788:Sox3 protein, Xenopus; C484457:Sox7 protein, Xenopus; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D029867:Xenopus Proteins; C418882:nodal5 protein, Xenopus; C418883:nodal6 protein, Xenopus; D003907:Dexamethasone