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.     

Bithorax phenocopy and pattern formation. I. Spatiotemporal characteristics of the phenocopy response

In four different lines of Drosophila melanogaster the highest frequencies of bithorax phenocopies result from ether treatment during the precellular blastoderm stages. The spatial characteristics of the phenocopy spots are dependent on the precise timing of phenocopy induction, and are not in accord with those predicted from the model of sequential determination of whole compartments put forward by Garcia-Bellido et al. in 1976. Ether treatment for 13 successive previous generations gave rise to changes in the spatiotemporal characteristics of the phenocopy response. Our results suggest the involvement of continuous diffusion-like processes in the prepatterning event which is affected by ether.     

No overall benefit of predator exclosure cages for the endangered St. Helena Plover Charadrius sanctaehelenae

Predator exclosure cages are designed to increase the clutch survival of ground‐nesting birds. Predator exclosures provided for the endangered St. Helena Plover Charadrius sanctaehelenae, however, did not result in differences in clutch survival between protected and control nests and may have resulted in elevated adult mortality. Exclosures did not exclude all cats, the dominant nest predator, and it is likely that cats caused the adult mortalities observed close to the exclosures. A population model indicates that even if predator exclosures had excluded all cats, the benefits of increased clutch survival would have been more than negated by the estimated decrease in adult survival. The overall effect of predator exclosures needs to be clarified for other species, taking into consideration annual productivity and adult survival, to understand the circumstances in which predator exclosures are beneficial.