Melanocytes Respond to Mechanical Stretch by Activation of Mitogen‐Activated Protein Kinases (MAPK)

Cells of human epidermis are permanently targeted by mechanical stimuli. Besides mechanical forces from external sources the body itself generates mechanical forces via muscle contractions and growth processes. Recently, it was demonstrated that mechanical stretch is connected to enhanced proliferation in epidermal cells. The underlying biochemical events are still a matter of debate. Here we show that mechanical stretch leads to activation of both ERK1/2 and SAPK/JNK in human melanocytes and keratinocytes. In response to a 5 min single stretch ERK1/2 becomes moderately induced in melanocytes and peaked 30 min after the stimulus. In keratinocytes strong activation of ERK1/2 is present directly after the stimulus. SAPK/JNK shows the same activation pattern in both cell species – a slow but steady activation. The different kinetics of both MAPK suggest that different signalling cascades were activated. Future studies should evaluate the relevance of stretch‐dependent MAPK activation in triggering the cell proliferation.     

Developmental strategies in an invasive spider: constraints and plasticity

1. Growth defines the major life‐history traits such as size, weight, and age at maturity that determine an organism's fitness. Different models have been developed to describe growth by means of geometric progressions (e.g. Dyar's rule). However, growth forced along a geometric trajectory might constrain a plastic response to variable environmental conditions (e.g. food availability). 2. The present study investigated growth patterns under varying food conditions in the bridge spider, Larinioides sclopetarius, an extremely successful species in colonising urban habitats. 3. In L. sclopetarius growth ratios of successive instars were not constant but decreased over development. Instead, these spiders' growth is well described by a developmental growth rate (weight gain per moult) and a growth coefficient (weight gain per development time), both of which are based on a geometric progression. All developmental parameters, including developmental growth rate and growth coefficient as well as the intermoult duration and the number of instars, highly depend on food availability in L. sclopetarius and thus show plasticity. 4. Our study shows that geometric growth patterns do not necessarily preclude plasticity and that the parameters of geometric growth are affected by developmental plasticity. We suggest that their high developmental plasticity may facilitate bridge spiders' success in invading urban habitats.