Meeting Abstract

87.4  Monday, Jan. 6 11:00  An ancient deuterostome anterior signaling center patterns and sizes the anterior neuroectoderm territory of the sea urchin embryo RANGE, R.C.*; ANGERER, R.C.; ANGERER, L.M.; Mississippi State University; National Institutes of Health, NIDCR; National Institutes of Health, NIDCR rangery@mail.nih.gov

Anterior signaling centers are essential to specify and pattern the early anterior neuroectoderm (ANE) of many deuterostome embryos, such as the vertebrate forebrain. In the sea urchin embryo, the ANE is restricted to the anterior end of the late blastula-stage embryo where it will form a simple centralized neural territory consisting of several types of neurons as well as the apical tuft. Here, we show that during early development, the sea urchin ANE separates into inner and outer regulatory domains expressing the cardinal ANE transcriptional regulators, FoxQ2 and Six3, respectively. This patterning process is driven by FoxQ2, which is required to eliminate six3 expression from the inner domain. FoxQ2 also activates the expression of two secreted Wnt regulators, sFrp1/5 and Dkk3, the activities of which determine the correct sizes of the inner and outer ANE territories. Furthermore, the levels of sFrp1/5 and Dkk3 are rigidly maintained via auto-repressive and cross-repressive interactions with Wnt signaling components and additional ANE transcription factors. Our data support a model in which Six3 and FoxQ2 initiate an anterior patterning center that implements correct size and positions of ANE structures. Comparisons of functional and expression studies in sea urchins, hemichordates and vertebrates show striking similarities in deuterostome ANE regulatory states and the molecular mechanisms that position and define ANE borders. These data provide strong support for the idea that the sea urchin embryo uses an ancient anterior patterning system that was present in the common ambulacrarian/chordate ancestor.