Visit our Expo - Redox and Inflammation signaling 2012

Session III : Protein kinase cascades as therapeutic targets Poster III, 58
The MEKK1-JNK Pathway Regulates Mouse Eyelid Morphogenesis
Atsushi Takatori and Ying Xia
Department of Environmental Health, University of Cincinnati Medical Center,
Cincinnati, Ohio 45267 U.S.A
MEK kinase 1 (MEKK1) is a mitogen-activated protein kinase kinase kinase, known as an
upstream regulator for the c-Jun NH2-terminal kinases (JNKs). Knocking out Mekk1 in mice
results in eye-open at birth (EOB) phenotype that leads to severe eye pathologies. There are
two Jnk isoforms, Jnk1 and Jnk2, that are ubiquitously expressed in various tissues. This
study is aimed at understanding the distinct role for JNK1 and JNK2 in transmitting the
MEKK1 signals during eyelid morphogenesis. Mekk1-/-, Jnk1-/- and Jnk2-/- mice were
backcrossed to C57BL/6 background and intercrosses were carried out to generate Mekk1+/-
Jnk1-/-and Mekk1+/-Jnk2-/- mice. We find that the Mekk1+/-Jnk1-/-, but not Mekk1+/-
Jnk2-/-, mice displayed EOB similar to the Mekk1-/- mice. Unlike the Mekk1+/-Jnk2-/-
fetuses, which showed a thin layer of eyelid epithelium covering the ocular surface at
embryonic day 16.5, the Mekk1+/-Jnk1-/- fetuses lacked eyelid closure and had fully exposed
cornea. Immunohistochemistry studies showed similar levels of JNK phosphorylation, but a
much reduced c-Jun phosphorylation and plasminogen activator inhibitor-1 (PAI-1)
expression in the developing eyelid epithelium of the Mekk1+/-Jnk1-/-, compared to that of
the wild type and the Mekk1+/-Jnk2-/- fetuses. Considering the crucial role of PAI-1 in
epithelial cell migration, we studied the keratinocyte migration using an in vitro wound
healing assay. Our results indicated that the Mekk1+/-Jnk1-/- keratinocytes had slower
wound closure than the wild type and Mekk1+/-Jnk2-/- keratinocytes. Taken together, our
results show that in the absence of JNK1, one functional Mekk1 allele is insufficient to cause
c-Jun phosphorylation and epithelial cell movement, responsible for defective eyelid
morphogenesis of the Mekk1+/-Jnk1-/- fetuses. JNK1 appears to be more critical than JNK2
in transmitting the MEKK1 signals to c-Jun phosphorylation and target gene expression
during mouse embryonic eyelid development.
Support: NIH EY 15227
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