The surprising complexity of the transcriptional regulation of the spdri gene reveals the existence of new linkages inside sea urchin's PMC and Oral Ectoderm Gene Regulatory Networks.

During sea urchin embryogenesis the spdri gene participates in two separate Gene Regulatory Networks (GRNs): the Primary Mesenchyme Cells' (PMCs) and the Oral Ectoderm's one. In both cases, activation of the gene follows initial specification events [Amore, G., Yavrouian, R., Peterson, K., Ransick, A., McClay, D., Davidson, E., 2003. Spdeadringer, a sea urchin embryo gene required separately in skeletogenic and oral ectoderm gene regulatory networks. Dev. Biol. 261, 55-81.]. We identified a portion of genomic DNA ("4.7IL" -3456;+389) which is sufficient to replicate sdpri's expression pattern in experiments of transgenesis, using a GFP reporter. In our experiments, the activation kinetic of 4.7IL-GFP was similar to that of the endogenous gene and the reporter responded to known spdri's transcriptional regulators (Ets1, Alx1, Gsc and Dri). Here we present a dissection of this regulatory region and a description of the modules involved in spdri's transcriptional regulation. Both in the PMCs' and Oral Ectoderm's expression phases, activation of spdri is obtained through the integration of three kinds of inputs: positive and globally distributed ones; negative ones (that prevent ectopic expression); positive and tissue-specific ones. Our results allow to expand the map of the regulatory connections at the spdri node, both in the PMCs and in the Oral Ectoderm Gene Regulatory Networks (GRNs).