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Originally published In Press as doi:10.1074/jbc.M110637200 on March 23, 2002
J. Biol. Chem., Vol. 277, Issue 22, 19806-19810, May 31, 2002
The Molecular Basis of Src Kinase Specificity during Vertebrate
Mesoderm Formation*
Joanne
Hama ,
Crystal
Suri ,
Tomomi
Haremaki, and
Daniel C.
Weinstein§
From the Department of Pharmacology and Biological Chemistry, Mount
Sinai School of Medicine, New York, New York 10029
Members of the Src family of non-receptor
tyrosine kinases play a critical role in mesoderm formation in the
frog, Xenopus laevis, acting as required
mediators downstream of the fibroblast growth factor receptor.
At least four members of this gene family, Src, Fyn, Yes, and Laloo,
are expressed during early embryonic development. Ectopic expression of
Laloo and Fyn, but not Src, induce mesoderm in ectodermal explants,
indicating that these factors are non-redundant during early vertebrate
development. Here we investigate the basis for the differential
activity of the Src and Laloo kinases during mesoderm formation. We
demonstrate that although both Src and Laloo physically interact with
the substrate protein SNT-1/FRS2 only Laloo phosphorylates SNT-1, an
event previously shown to be required for the activity of the latter
and for mesoderm induction in vivo. We show that Src is enzymatically capable of stimulating mesoderm formation, as an activated Src construct both phosphorylates SNT-1 and induces mesoderm
in explant cultures. However, a chimeric Laloo construct containing a
Src C-terminal tail is inactive, suggesting that the early embryo
contains a specific Laloo-activating, or Src-inactivating, factor.
Finally, through further chimeric analysis, we provide evidence
to suggest that differences in Laloo and Src activity are also mediated
by the SH2, SH3, and kinase domains of these molecules.
*
This work was supported by an Irma T. Hirschl Career
Scientist Award, by the Speaker's Fund for Biomedical Research: Toward the Science of Patient Care, awarded by the City of New York, by the
AMDeC (Academic Medicine Development Company) Foundation of New York
City, through its Tartikoff/Perelman/Entertainment Industry Fund for
Young Investigators in Women's Cancers, and by United States Public
Health Service Grant R01-GM61671 (all to D. C. W.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Members of the graduate training program in molecular, cellular,
biochemical, and developmental sciences.
§
To whom correspondence should be addressed: Dept. of
Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, 1 Gustave L. Levy Pl., Box 1215, New York, NY 10029. Tel.:
212-659-1721; Fax: 212-831-0114; E-mail: weinsd01@doc.mssm.edu.
Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2002 by the American Society for Biochemistry and Molecular Biology.
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