Fundamental stimulus for erythropoietin production in the neonatal rat

A mild degree of hemolytic anemia was induced in neonatal rats by a single subcutaneous injection with phenylhydrazine (PHZ). The ability to respond to this challenge was determined by monitoring serum erythropoietin (EP) levels at 6 and 12 hr. At 6 hr after PHZ, EP reached a level of 4.25 ± 1.03 U/ml, and at the 12-hr interval it had increased to 6.12 ± 1.49 U/ml. Based on these data, it is our suggestion that PHZ-induced hemolysis affords an effective stimulus for EP production in the neonatal rodent.     

Identification of major common extracellular proteins secreted by Aeromonas salmonicida strains isolated from diseased fish

Ten different strains of Aeromonas salmonicida that were isolated from diseased fish were grown under identical conditions (24 h at 25 degree C) in 3% (wt/vol) tryptone soya broth medium supplemented with vitamins and inorganic ions. In each case the extracellular proteins that were formed were compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it was found that there were two significant common components, one with a molecular weight of 70,000 and the other with a weight of 56,000. Application of enzyme purification techniques to the supernatant fraction proteins of a culture of one of the strains resulted in the isolation of a 70-kilodalton (kDa) component, which was found to be a serine protease, and a 56-kDa component, which was hemolytic to trout erythrocytes. Rocket immunoelectrophoresis with rabbit antibodies to the isolated protease and hemolysin showed the same antigenic components in the supernatant fractions of all the cultures. These activities were assayed, and protease activity was found to vary by a factor of three, from 59 to 195 U/ml, while the range of hemolytic activity was over a narrow band, from 28 to 43 U/ml. There was an inconsistency between the immunoelectrophoretic and direct assay data in only one case. This indicated the presence of additional hemolytic activity, in addition to the 56-kDa component. The detection of large amounts of the same protease and hemolysin, two potent degradative activities, in a random series of strains of A. salmonicida suggests that they may be obligatory virulence factors in the development of furunculosis.     

Evolvability of the Cichlid Jaw: New Tools Provide Insights into the Genetic Basis of Phenotypic Integration

Phenotypic integration is a phenomenon that manifests itself as the covariation among traits, and is thought to substantially influence how evolution unfolds, both in terms of rate and direction, which ultimately determines evolvability. To date little is known about how integration may change across an adaptive radiation, nor do we have a way of determining its genetic basis. Here we sought to test the hypotheses that (1) higher magnitudes of integration are associated with a greater degree of eco-morphological divergence, and (2) integration has a tractable genetic basis. To this end, we first evaluated the magnitude of integration at the population level in the lower jaws of two Lake Malawi cichlid species that exhibit different degrees of trophic specialization. We find that the more eco-morphologically divergent species does indeed exhibit a significantly higher magnitude of integration, which is consistent with our first hypothesis. Next, we developed a new statistical approach based on jackknife pseudovalues to produce a quantitative trait representative of inter-individual variation in the magnitude of integration. This metric was successfully applied to map the genetic basis of integration in the lower jaws of F2 hybrids derived from the two parental species that exhibited differences in the magnitude of integration. We detected three QTLs and two epistatic interactions that contribute to variation in integration within the cichlid mandible. We also detected a single QTL for lower jaw shape. None of the single QTLs for integration identified here overlapped with the interval for lower jaw shape, although one of the epistatic loci for integration did overlap with shape QTL. These results underscore a complex relationship between integration and shape, but suggest largely distinct genetic bases for these two traits. In all, our results show that phenotypic integration has a tractable, yet complex, genetic basis and that we now have the tools available to shed new light on the mechanisms that both promote and limit craniofacial diversity.