Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.     

Genetic population structure of the large blue butterfly Maculinea alcon in Denmark

We have investigated the genetic population structure within and the genetic differentiation between local populations of the large blue butterfly Maculinea alcon throughout the Jutland peninsula. Samples were collected as eggs on foodplants (Gentiana pneumonanthe), and reared to 4th instar caterpillars in the laboratory. A significant excess of homozygotes was found for all the investigated allozyme loci in most of the populations. A North-South cline was observed for the allele frequencies at some of the loci and for several linkage groups. Because some of the allele frequency clines were parallel to clines in adult morphological variation, we interpret our results as evidence for the co-existence of at least two gene pools within the Danish Maculinea alcon populations. Multilocus electrophoretic data revealed highly positive but variable FST values, which under this scenario would reflect varying frequencies of the Maculinea gene pools across the local populations. The significantly positive FIS values indicate that these gene pools are at least partly reproductively isolated (Wahlund effect). The co-occurrence of several Maculinea alcon gene pools on many local sites in Jutland is of great importance for conservation of the fragmented Maculinea populations. Our results show that there is probably more Maculinea biodiversity to conserve than was previously thought, and suggests that extant populations are more fragmented and vulnerable than counts of flying adults or eggs on foodplants indicate.