Biomedical Engineering – From Theory to Applications

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Biomedical Engineering – From Theory to Applications
among different species, but it is always quantifiable by standardized protocols in terms of
median lethal concentration and median lethal time (LC50 and LT50). For this reason short
term (lethality) and long-term (sub-lethality) tests based on the evaluation of polyp
morphology, reproductive activity and regeneration efficiency, can be used to test the
potential toxicity/teratogenic effect of any kind of medium suspended compound.
Beside the effects detectable at macroscopic level, the availability of the genome sequence
makes it possible to study the molecular mechanisms and gene pathways activated by the
addition of external (chemical or physical) stressors. One of the main outcomes of the genomic
sequencing projects of cnidarian species (corals, anemones, jellyfish and Hydras) (Chapman et
al., 2010; Putnam et al., 2007) is the recognition that many genes, including those associated
with diseases, are conserved in evolution from yeast to man (Steele et al., 2011). Remarkably, a
surprisingly complexity was found in cnidarian genomes, in the range of higher vertebrates,
while other invertebrates routinely used as model organisms, such as the fruit fly Drosophila
melanogaster or the flatworm Caernorabditis elegans, have lost during speciation many genes
belonging to the common eumetazoan primitive ancestor. In Hydra, the key pathways
underlying development, regeneration and re-aggregation have been identified and their
characterization showed the presence of almost complete gene repertoires: the canonical and
non canonical Wnt pathways for maintaining and re-establishing apical organizer activity and
for cellular evagination processes, respectively; the BMP/chordin pathway for axis patterning;
the MAPK– CREB pathway for head regeneration; the FGF pathway for bud detachment, and
the Notch pathway for differentiating some interstitial cell lineages (reviewed by Galliot, 2010;
Galliot and Ghila, 2010).
Fig. 2. The regeneration process in Hydra vulgaris
Hydra body column has a high capacity for regeneration of both the head and foot. Because of
the tissue dynamics that take place in adult Hydra, the processes governing axial patterning are
continuously active to maintain the form of the animal. Following amputation at mid-gastric
level, the two polyp halves immediately initiate an asymmetric process at the wound site: the