First published online March 20, 2009
Development 136, 804e (2009)
© The Company of Biologists Limited
Cadherin function: right place, right time
Cadherins are a large family of cell-cell adhesion receptors, but despite
intense research into their functions, many aspects of their activity remain
somewhat elusive. Two papers in this issue of Development now shed
new light on the significance of both cell-type specific cadherin expression
and their subcellular localisation for their roles in development.
In the first study (p.
1327), Christopher Wylie and co-workers report that, in
Xenopus ectoderm, distinct morphogenetic movements result from actin
assembly mediated by differential cadherin expression. The authors show that
the Type I sub-family members C-, E- and N-cadherin all assemble cortical
actin. They then analysed the localisation of these three cadherins in the
developing ectoderm, which separates into two parts (neural and non-neural).
The cadherins, they find, are temporally and spatially differentially
expressed in the neural and non-neural ectoderm; where expression domains
overlap, the cadherins are predominantly found in different subcellular
locations. In addition, whereas N-cadherin depletion affects actin assembly
in, and the morphogenetic movements of, neural ectoderm, E-cadherin depletion
has similar effects in the non-neural ectoderm. The two cadherins, however,
cannot replace each other in rescue experiments. Thus, the researchers
propose, cadherins are important for actin assembly during morphogenesis, and
their differential expression is crucial for generating distinct morphogenetic
movements.
In the second study, Mahendra Sonawane, Christiane Nüsslein-Volhard
and colleagues investigate cellular junction assembly in zebrafish and report
that E-cadherin is involved in regulating this process
(p. 1231). The authors
find that during the formation of hemidesmosomes, a type of cell junction that
links the basal domain of epithelial cells to the extracellular matrix,
E-cadherin and the polarity regulator Lgl2 localise to the lateral domain of
epithelial cells. By contrast, the hemidesmosome component Integrin alpha 6
(Itga6) localises to both the lateral and the basal domain. The authors then
demonstrate that Lgl2 promotes the targeting of Itga6 to the basal membrane
during hemidesmosome formation, whereas E-cadherin negatively regulates this
process. Thus, two proteins localised to the lateral domain act
antagonistically to regulate basal hemidesmosome formation. Together, these
two studies highlight the context-dependent nature of cadherin interactions
and indicate that their function might be influenced by their subcellular
localisation.
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