Cell migration is essential for embryonic development, it occurs in adult
organisms during processes like wound healing and its misregulation contributes
to pathological conditions such as metastasis. Despite this, most studies of cell
migration have been undertaken in vitro. Ena/VASP proteins, believed to be
actin anti-capping proteins, have been studied extensively in fibroblasts in vitro,
and using Drosophila macrophages (hemocytes) within the developing embryo,
the role of the Drosophila homologue of Mena, Ena, is investigated in vivo.
Consistent with data from fibroblasts in vitro, Ena localised to regions of actin
dynamics within migratory hemocytes, where this protein stimulated
lamellipodial dynamics and positively regulated filopodial number and length.
However, whilst overexpression of Ena/VASP proteins in fibroblasts reduced
migration speeds, Ena overexpression in hemocytes dramatically increased
migration speeds in three different assays. This positive regulation of migration
speed closely resembled the increased motility of breast cancer cells that
overexpress Mena and evidence presented here, suggests that this key difference
may be explained by spatial constraints that are imposed upon cells within three dimensional environments. Indeed, such constraints prevented ruffling, a more
detrimental form of retraction, in hemocytes in vivo. Furthermore, fibroblasts
overexpressing Mena in vitro form membrane ruffles more frequently. Therefore
Ena/VASP proteins drive migration by enhancing lamellipodial protrusion, but in
certain environments these protrusions are lost as ruffles slowing migration.
The method by which Ena regulates lamellipodial protrusion and migration
speeds was then investigated: Ena increased Fascin-mediated actin bundling and
the number of Fascin rich-actin bundles that coalesced. Analysis of individual
actin bundles revealed that coalescence increased protrusion rate and that both
protrusion rate and coalescence, increased cell migration speeds. This suggests
that Ena facilitates an increase in cell migration by promoting the coalescence of
Fascin bundles, and positions Ena as a key regulator of migration speeds in vivo.
|Date of Award||29 Sep 2011|
|Supervisor||William Wood (Supervisor) & Iwan Evans (Supervisor)|
- cell migration