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Published January 1, 2016 | Supplemental Material
Journal Article Open

Cis-regulatory control of the initial neurogenic pattern of onecut gene expression in the sea urchin embryo

Abstract

Specification of the ciliated band (CB) of echinoid embryos executes three spatial functions essential for postgastrular organization. These are establishment of a band about 5 cells wide which delimits and bounds other embryonic territories; definition of a neurogenic domain within this band; and generation within it of arrays of ciliary cells that bear the special long cilia from which the structure derives its name. In S. purpuratus the spatial coordinates of the future ciliated band are initially and exactly determined by the disposition of a ring of cells that transcriptionally activate the onecut homeodomain regulatory gene, beginning in blastula stage, long before the appearance of the CB per se. Thus the cis-regulatory apparatus that governs onecut expression in the blastula directly reveals the genomic sequence code by which these aspects of the spatial organization of the embryo are initially determined. We screened the entire onecut locus and its flanking region for transcriptionally active cis-regulatory elements, and by means of BAC recombineered deletions identified three separated and required cis-regulatory modules that execute different functions. The operating logic of the crucial spatial control module accounting for the spectacularly precise and beautiful early onecut expression domain depends on spatial repression. Previously predicted oral ectoderm and aboral ectoderm repressors were identified by cis-regulatory mutation as the products of goosecoid and irxa genes respectively, while the pan-ectodermal activator SoxB1 supplies a transcriptional driver function.

Additional Information

© 2015 Elsevier. Received date: 5 August 2015; Revised date: 1 October 2015; Accepted date: 16 October 2015; Available online 30 October 2015. This work is dedicated to the memory of my mentor Eric H. Davidson (1937–2015) whose understanding of biology has shaped the field of embryogenesis in general, and the trajectory of my research in particular. I would like to express my gratitude to Jongmin Nam for having developed the multiplex enhancer assay that served as the cornerstone for this study; to Niles Pierce for HCR in situ reagents; to Julie Hahn and Erika Vielmas for their assistance in generating BAC deletions; and to Patrick Leahy for sourcing the animals utilized in this study - J.C.B. The authors declare no competing or financial interests. Author contributions: J.C.B. & E.H.D. designed the research; J.C.B. performed the research; J.C.B. & E.H.D. analyzed the data; and J.C.B. & E.H.D. wrote the paper. This research was supported by the National Institutes of Health [HD067454 to E.H.D.].

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