Click
here to close Hello! We notice that
you are using Internet Explorer, which is not supported by Echinobase
and may cause the site to display incorrectly. We suggest using a
current version of Chrome,
FireFox,
or Safari.
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.
Figure 1. Left-right asymmetry in the sea urchin.During cleavage, mesoderm (red cells at 60-cell stage) and small micromeres (purple cells at vegetal pole) become specified. At the end of gastrulation, progeny of these two cell types contribute to the coelomic pouches (red and purple outpockets seen at the tip of the archenteron). During larval stages, the adult rudiment grows from the left coelomic pouch. After metamorphosis, that rudiment grows to become the adult. Embryonic axes are shown relative to the 60-cell cleavage and gastrula stages. The aboral-oral axis is also known as the dorsal-ventral axis. The animal-vegetal axis is the only axis established prior to fertilization. Oral-aboral axis specification occurs early in cleavage, and left-right axis determination occurs at the late gastrula stage.
Duboc,
Left-right asymmetry in the sea urchin embryo is regulated by nodal signaling on the right side.
2005, Pubmed,
Echinobase
Duboc,
Left-right asymmetry in the sea urchin embryo is regulated by nodal signaling on the right side.
2005,
Pubmed
,
Echinobase
Duboc,
Nodal and BMP2/4 signaling organizes the oral-aboral axis of the sea urchin embryo.
2004,
Pubmed
,
Echinobase
Levin,
A molecular pathway determining left-right asymmetry in chick embryogenesis.
1995,
Pubmed
Luo,
Opposing nodal and BMP signals regulate left-right asymmetry in the sea urchin larva.
2012,
Pubmed
,
Echinobase
Nonaka,
De novo formation of left-right asymmetry by posterior tilt of nodal cilia.
2005,
Pubmed
Nonaka,
Randomization of left-right asymmetry due to loss of nodal cilia generating leftward flow of extraembryonic fluid in mice lacking KIF3B motor protein.
1998,
Pubmed
Schier,
Molecular genetics of axis formation in zebrafish.
2005,
Pubmed
Spéder,
Strategies to establish left/right asymmetry in vertebrates and invertebrates.
2007,
Pubmed
Vandenberg,
Far from solved: a perspective on what we know about early mechanisms of left-right asymmetry.
2010,
Pubmed
Vincent,
Cell fate decisions within the mouse organizer are governed by graded Nodal signals.
2003,
Pubmed
Yajima,
Small micromeres contribute to the germline in the sea urchin.
2011,
Pubmed
,
Echinobase
