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XB-ART-44583
Curr Biol January 10, 2012; 22 (1): 33-9.

Serotonin signaling is required for Wnt-dependent GRP specification and leftward flow in Xenopus.

Beyer T , Danilchik M , Thumberger T , Vick P , Tisler M , Schneider I , Bogusch S , Andre P , Ulmer B , Walentek P , Niesler B , Blum M , Schweickert A .


Abstract
In vertebrates, most inner organs are asymmetrically arranged with respect to the main body axis [1]. Symmetry breakage in fish, amphibian, and mammalian embryos depends on cilia-driven leftward flow of extracellular fluid during neurulation [2-5]. Flow induces the asymmetric nodal cascade that governs asymmetric organ morphogenesis and placement [1, 6, 7]. In the frog Xenopus, an alternative laterality-generating mechanism involving asymmetric localization of serotonin at the 32-cell stage has been proposed [8]. However, no functional linkage between this early localization and flow at neurula stage has emerged. Here, we report that serotonin signaling is required for specification of the superficial mesoderm (SM), which gives rise to the ciliated gastrocoel roof plate (GRP) where flow occurs [5, 9]. Flow and asymmetry were lost in embryos in which serotonin signaling was downregulated. Serotonin, which we found uniformly distributed along the main body axes in the early embryo, was required for Wnt signaling, which provides the instructive signal to specify the GRP. Importantly, serotonin was required for Wnt-induced double-axis formation as well. Our data confirm flow as primary mechanism of symmetry breakage and suggest a general role of serotonin as competence factor for Wnt signaling during axis formation in Xenopus.

PubMed ID: 22177902
Article link: Curr Biol

Genes referenced: cat.2 ctnnb1 dvl2 foxj1 foxj1.2 gal.2 nodal nodal1 nodal3.1 nodal3.2 pitx2 rpsa sia1 tekt2 wnt8a
Morpholinos: htr3a MO1 htr3a MO2


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