Left-Right Asymmetry in the Sea Urchin Embryo: BMP and the Asymmetrical Origins of the Adult

Jacob F Warner,David R Mcclay,Deirdre C Lyons

doi:10.1371/journal.pbio.1001404

Abstract

Bilateral animals, including humans and most metazoans, are not perfectly symmetrical. Some internal structures are distributed asymmetrically to the right or left side. A conserved Nodal and BMP signaling system directs molecular pathways that impart the sidedness to those asymmetric structures. In the sea urchin embryo, one such asymmetrical structure, oddly enough, is the entire adult, which grows out of left sided structures produced in the larva. In a paper just published in PLOS Biology, BMP signaling is shown to be necessary early in larval development to initiate the asymmetric specification of one of those left-sided structures, called the left coelomic pouch. This study reports that BMP signaling activates a group of transcription factors asymmetrically in the left coelomic pouch only, which launch the pathway that eventually leads to the formation of the adult that emerges from the larva at metamorphosis.

Highlights

Bilateral animals, including humans and most metazoans, are not perfectly symmetrical
Two coelomic pouches bud from the anterior end of the foregut, and these structures exhibit left-right asymmetry
In 2005, Nodal was discovered to participate in establishing L-R asymmetry in sea urchin embryos as well, but in sea urchins, rather than being expressed on the left side, Nodal was expressed on the right side, where it was shown to inhibit the right coelomic pouches (CPs) from forming the adult rudiment

Summary

Introduction

Bilateral animals, including humans and most metazoans, are not perfectly symmetrical. That future adult body cavity is called a coelom, and its lining originates in the sea urchin from the mesodermal coelomic pouches (CPs). During larval growth in the sea urchin, the left CP becomes modified and produces major components of the rudiment (the term used for the primitive form of the adult) (Figure 1).

Results

Conclusion