The African clawed frog, Xenopus laevis, begins development as a compact ball of cells that undergoes a dramatic transformation through cell migrations and positional rearrangements that result in the separation of the embryo into three distinct germ layers, which go on to give rise to all of the tissues and structures in the adult animal's body. During this transformation, known as gastrulation, the embryo changes from a roughly spherical shape to an elongated, streamlined form through a process called convergent extension (CE), in which polarized cells migrate to and merge at the embryo's midline, driving it to lengthen along its anterior-posterior axis.

A number of genes involved in the regulation of convergent extension have been identified in amphibians and other vertebrates, such as zebrafish, but the picture of the underlying molecular mechanisms remains incomplete. Researchers at the RIKEN Center for Developmental Biology (CDB; Kobe, Japan) have now added a new piece to the puzzle. In a report published in the advanced online edition of Nature Cell Biology, Noriaki Sasai and colleagues in the Laboratory for Organogenesis and Neurogenesis (Group Director, Yoshiaki Sasai) show that the product of the gene NRH1 is essential to the regulation of CE movements in the frog.

While performing a screen of genes expressed in the posterior neuroectoderm, Sasai et al. identified a gene encoding a protein that showed similarities to p75NTR, a neurotrophin receptor. (Neurotrophins are molecules that function in the survival, growth and migration of neurons.) However, on testing its affinity for neurotrophin ligands, the group found that, unlike p75NTR, NRH1 did not bind with neurotrophins, which led them to seek other biological roles for the protein.

Experiments in which NRH1 was overexpressed by injecting its messenger RNA directly into very early (4-cell stage) embryos resulted in shortening of the body axis and the failure of mesodermal and neu
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Contact: Doug Sipp
sipp@cdb.riken.jp
81-78-306-3043
RIKEN Center for Developmental Biology
20-Jul-2004

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