Transcriptional regulation of the Ciona Gsx gene in the neural plate

Work by R. E. in the laboratory of H. Y. was supported by a European Molecular Biology Organisation (EMBO) short term fellowship (ASTF 534–2014). Work by P. L. and E. F. was supported by CNRS and the Agence Nationale de la Recherche (ANR-13-BSV2–0011-01,TED; ANR-08-BLAN-0067, Chor-Evo-Net). Work by R. E., A. P. and L. S. in the laboratory of A. S. was supported by SZN PhD fellowships. The group of D. E. K. F. is supported by the Leverhulme Trust (RPG-2016-351). Isolation of the Gsx containing cosmid was conducted in the laboratory of Peter Holland and supported by the Biotechnology and Biological Sciences Research Council (BBSRC) (no. G09218).The ascidian neural plate consists of a defined number of identifiable cells organized in a grid of rows and columns, representing a useful model to investigate the molecular mechanisms controlling neural patterning in chordates. Distinct anterior brain lineages are specified via unique combinatorial inputs of signalling pathways with Nodal and Delta-Notch signals patterning along the medial-lateral axis and FGF/MEK/ERK signals patterning along the anterior-posterior axis of the neural plate. The Ciona Gsx gene is specifically expressed in the a9.33 cells in the row III/column 2 position of anterior brain lineages, characterised by a combinatorial input of Nodal-OFF, Notch-ON and FGF-ON. Here, we identify the minimal cis-regulatory element (CRE) of 376 bp, which can recapitulate the early activation of Gsx. We show that this minimal CRE responds in the same way as the endogenous Gsx gene to manipulation of FGF- and Notch-signalling pathways and to overexpression of Snail, a mediator of Nodal signals, and Six3/6, which is required to demarcate the anterior boundary of Gsx expression at the late neurula stage. We reveal that sequences proximal to the transcription start site include a temporal regulatory element required for the precise transcriptional onset of gene expression. We conclude that sufficient spatial and temporal information for Gsx expression is integrated in 376 bp of non-coding cis-regulatory sequences.PostprintPeer reviewe