A Requirement for Zic2 in the Regulation of Nodal Expression Underlies the Establishment of Left-Sided Identity
Dykes IM., Szumska D., Kuncheria L., Puliyadi R., Chen C-M., Papanayotou C., Lockstone H., Dubourg C., David V., Schneider JE., Keane TM., Adams DJ., Brown SDM., Mercier S., Odent S., Collignon J., Bhattacharya S.
AbstractZIC2mutation is known to cause holoprosencephaly (HPE). A subset ofZIC2HPE probands harbour cardiovascular and visceral anomalies suggestive of laterality defects. 3D-imaging of novel mouseZic2mutants uncovers, in addition to HPE, laterality defects in lungs, heart, vasculature and viscera. A strong bias towards right isomerism indicates a failure to establish left identity in the lateral plate mesoderm (LPM), a phenotype that cannot be explained simply by the defective ciliogenesis previously noted in Zic2 mutants. Gene expression analysis showed that the left-determining NODAL-dependent signalling cascade fails to be activated in the LPM, and that the expression ofNodalat the node, which normally triggers this event, is itself defective in these embryos. Analysis of ChiP-seq data,in vitrotranscriptional assays and mutagenesis reveals a requirement for a low-affinity ZIC2 binding site for the activation of theNodalenhancer HBE, which is normally active in node precursor cells. These data show that ZIC2 is required for correctNodalexpression at the node and suggest a model in which ZIC2 acts at different levels to establish LR asymmetry, promoting both the production of the signal that induces left side identity and the morphogenesis of the cilia that bias its distribution.