Chaotic gene regulatory networks can be robust against mutations and noise

Robustness to mutations and noise has been shown to evolve through stabilizing selection for optimal phenotypes in model gene regulatory networks. The ability to evolve robust mutants is known to depend on the network architecture. How do the dynamical properties and state-space structures of networks with high and low robustness differ? Does selection operate on the global dynamical behavior of the networks? What kind of state-space structures are favored by selection? We provide damage propagation analysis and an extensive statistical analysis of state spaces of these model networks to show that the change in their dynamical properties due to stabilizing selection for optimal phenotypes is minor. Most notably, the networks that are most robust to both mutations and noise are highly chaotic. Certain properties of chaotic networks, such as being able to produce large attractor basins, can be useful for maintaining a stable gene-expression pattern. Our findings indicate that conventional measures of stability, such as damage propagation, do not provide much information about robustness to mutations or noise in model gene regulatory networks.     

An assessment of impact strength of the mandible

In this study, an animal biomechanical study was performed to investigate the absorbed energy and impact strength of the mandible in relation to specimen position. Four regions of mandibles were loaded as complete pieces and gripped by the jaw of an Izod impact tester. All tests were carried out wet using the Izod impact test under two different impact loading directions, lateral and ventral.Absorbed energy and impact strength in kilojoules per square meter of specimen area were determined for each specimen. Under lateral impact loading, the absorbed energy was lowest for the anterior section due to the mental foramen's notch effect. The premolar region demonstrated more absorbed energy per unit area, or impact strength, than any other region. However, due to its small cross-sectional area, the premolar region also absorbs less impact energy.Under ventral impact loading conditions, anterior region absorbed twice as much impact energy than under lateral loading conditions. Premolar region absorbed the same impact energy under both lateral and ventral loading. Interestingly, mandibular angle under ventral loading absorbed five times more impact energy than under lateral loading. This behaviour is considered to be a mechanical adaptation to the actual loading of the mandible in vivo.     

Connexin 26 (GJB2) mutations in the Turkish population: implications for the origin and high frequency of the 35delG mutation in Caucasians

Mutations in the Connexin 26 (GJB2/Cx26) gene are responsible for more than half of all cases of prelingual non-syndromic recessive deafness in many Caucasian populations. To determine the importance of Cx26 mutations as a cause of deafness in Turks we screened 11 families with prelingual non-syndromic deafness, seven (64%) of which were found to carry the 35delG mutation. We subsequently screened 674 Turkish subjects with no known hearing loss and found twelve 35delG heterozygotes (1.78%; 95% confidence interval: 0.9%-3%) but no examples of the 167delT mutation. To search for possible founder effects, we typed chromosomes carrying the 35delG mutation for closely linked polymorphic markers in samples from Turkey and United States and compared the allele frequencies with those of hearing subjects. The data showed a modest degree of disequilibrium in both populations. Analyses of two pedigrees from Turkey demonstrated both conserved and different haplotypes, suggesting possible founder effects and multiple origins of the 35delG mutation.