Secreted frizzled related protein is a target of PaxB and plays a role in aquiferous system development in the freshwater sponge, Ephydatia muelleri.

Chelsea Hall,Omar A Quintero,Josephine Garcia,Malcolm S Hill,Melanie Rodriguez,Erik Wictor,Ajna S Rivera,Dora Posfai,Rachel Dumez,April L Hill,Michael Klymkowsky

doi:10.1371/journal.pone.0212005

Abstract

Canonical and non-canonical Wnt signaling, as well as the Pax/Six gene network, are involved in patterning the freshwater sponge aquiferous system. Using computational approaches to identify transcription factor binding motifs in a freshwater sponge genome, we located putative PaxB binding sites near a Secreted Frizzled Related Protein (SFRP) gene in Ephydatia muelleri. EmSFRP is expressed throughout development, but with highest levels in juvenile sponges. In situ hybridization and antibody staining show EmSFRP expression throughout the pinacoderm and choanoderm in a subpopulation of amoeboid cells that may be differentiating archeocytes. Knockdown of EmSFRP leads to ectopic oscula formation during development, suggesting that EmSFRP acts as an antagonist of Wnt signaling in E. muelleri. Our findings support a hypothesis that regulation of the Wnt pathway by the Pax/Six network as well as the role of Wnt signaling in body plan morphogenesis was established before sponges diverged from the rest of the metazoans.

Highlights

While it is well established that the Kingdom Animalia is monophyletic, and that the Cnidaria and bilaterians are sister groups, the phylogenetic placement of the earliest branching, nonbilaterian animal lineages is currently a point of vigorous debate (e.g., [1,2,3,4,5,6])
We show that EmSFRP is expressed during E. muelleri development and in amoeboid cells with filipodial-like projections in the choanosome and at the periphery of pinacodermal growth. dsRNA directed to EmSFRP leads to formation of additional oscula supporting a hypothesis that Secreted Frizzled Related Protein (SFRP) may act as an antagonist of Wnt signaling in E. muelleri
Likelihood that downstream targets are regulated by EmPaxB were ranked by the compare algorithm based on the number of putative EmPaxB binding sites that were found within 2000 bp of a putative protein coding sequence

Summary

Introduction

While it is well established that the Kingdom Animalia is monophyletic, and that the Cnidaria and bilaterians are sister groups, the phylogenetic placement of the earliest branching, nonbilaterian animal lineages (i.e., the Porifera and Ctenophora) is currently a point of vigorous debate (e.g., [1,2,3,4,5,6]). Regardless of the precise phylogenetic placement of sponges and ctenophores, our knowledge of all aspects of the biology of the extant metazoans will expand through detailed examination of these two poorly studied key animal lineages [8]. A central feature of the sponge body plan is a branched water canal system, and this constitutes the main body axis of sponges [14]. Despite the simple body axis (i.e., ostia to oscula), many complex aspects of metazoan organization, structures, and development are contained in the sponge body. Genetic, and developmental mechanisms that underlie the morphogenesis of the sponge aquiferous system will shed light on our understanding of sponge body plans and may provide clues about the development of more complex animal forms

Methods

Results

Conclusion