First published online September 7, 2007
Development 134, 1901e (2007)
© The Company of Biologists Limited
Mesoderm spreads HOW?
During gastrulation in Drosophila embryos, mesoderm cells
invaginate and then spread evenly over the ectoderm. Even spreading is
essential for the patterning of the mesoderm by ectodermal signals but is
defective in embryos mutant for the RNA-binding protein Held out wings (HOW).
Now, on p. 3473,
Toledano-Katchalski and co-workers report that HOW regulates mesoderm
spreading in a novel manner - by downregulating several mRNA species. The
researchers used microarray screening to identify four mRNAs with increased
mesodermal expression in how mutant embryos early in development - a
time when only the HOW(L) isoform (a post-transcriptional repressor) is
expressed. All four mRNAs bind specifically to HOW via their 3'UTRs, an
interaction that leads to mRNA degradation. Overexpression of one of the mRNAs
- miple, the Drosophila homolog of midkine and pleiotrophin
(vertebrate proteins involved in cell migration) - causes mesoderm spreading
defects and scattered activation of MAPK in mesodermal cells. Many tissues
express HOW(L) and its vertebrate homolog quaking (QKI) early in development,
so repression of specific RNAs might be an important developmental control
mechanism.

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Related articles in Development:
- Post-transcriptional repression of the Drosophila midkine and pleiotrophin homolog miple by HOW is essential for correct mesoderm spreading
- Hila Toledano-Katchalski, Ronit Nir, Gloria Volohonsky, and Talila Volk
Development 2007 134: 3473-3481.
[Abstract]
[Full Text]