Canonical and non-canonical Wnt signaling pathways define the expression domains of Frizzled 5/8 and Frizzled 1/2/7 along the early anterior-posterior axis in sea urchin embryos

• Published in: Developmental biology Vol. 444; no. 2; pp. 83 - 92
• Main Author: Range, Ryan C.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-12-2018
• Subjects: Animals; Anterior-posterior; Blastomeres - metabolism; Blastula - metabolism; Body Patterning - genetics; Deuterostome evolution; Frizzled Receptors - genetics; Frizzled Receptors - physiology; Fzl1/2/7; Fzl5/8; Gastrula - metabolism; Gene Expression Regulation, Developmental - genetics; Gene regulatory networks; Neural Plate - embryology; Sea Urchins - embryology; Sea Urchins - genetics; Spatio-Temporal Analysis; Transcription Factors - metabolism; Wnt Proteins - metabolism; Wnt signal transduction; Wnt Signaling Pathway; Gene regulatory networks; Anterior-posterior; Fzl1/2/7; Fzl5/8; Wnt signal transduction; Deuterostome evolution
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1016/j.ydbio.2018.10.003

The spatiotemporal expression of Frizzled receptors is critical for patterning along the early anterior-posterior axis during embryonic development in many animal species. However, the molecular mechanisms that regulate the expression of Frizzled receptors are incompletely understood in any species. In this study, I examine how the expression of two Frizzled receptors, Fzl1/2/7 and Fzl5/8, is controlled by the Wnt signaling network which directs specification and positioning of early regulatory states along the anterior-posterior (AP) axis of sea urchin embryos. I used a combination of morpholino- and dominant negative-mediated interference to knock down each Wnt signaling pathway involved in the AP Wnt signaling network. I found that the expression of zygotic fzl5/8 as well as that of the anterior neuroectoderm gene regulatory network (ANE GRN) is activated by an unknown broadly expressed regulatory state and that posterior Wnt/β-catenin signaling is necessary to down regulate fzl5/8's expression in posterior blastomeres. I show that zygotic expression of fzl1/2/7 in the equatorial ectodermal belt is dependent on an uncharacterized regulatory mechanism that works in the same cells receiving the TGF-β signals patterning this territory along the dorsal-ventral axis. In addition, my data indicate that Fzl1/2/7 signaling represses its own expression in a negative feedback mechanism. Finally, we discovered that a balance between the activities of posterior Wnt8 and anterior Dkk1 is necessary to establish the correct spatial expression of zygotic fzl12/7 expression in the equatorial ectodermal domain during blastula and gastrula stages. Together, these studies lead to a better understanding of the complex interactions among the three Wnt signaling pathway governing AP axis specification and patterning in sea urchin embryos.
•Spatiotemporal expression of fzl1/2/7 and fzl5/8 is remarkably similar in early invertebrate deuterostome embryos.•A broadly active regulatory mechanism activates the anterior neuroectoderm gene regulatory network in sea urchin embryos.•The sea urchin AP Wnt network controls the spatiotemporal expression of fzl1/2/7 and fzl5/8 during early development.•A balance among anterior and posterior secreted Wnt modulators establishes zygotic fzl1/2/7 expression in the ectoderm.