Pattern of dental eruption,skeletal maturation and stress in a Medieval Population from Sudanese Nubia

The present research represents a comparison of dental and skeletal development as a means for determining nutritional stress in a Medieval Christian population from Nubia’sBatn el Hajar. The sample consists of 21 individuals from an early Christian (c 550–750) and 23 individuals from a late Christian cemetery (c mid-16th century) excavated from the site of Kulubnarti, Sudan. Ages at death ranged from 12 to 23 years. For the combined sample, a large majority (70.5%) of individuals had skeletal ages younger than their dental ages. However, a comparison of those individuals that could be sexed revealed that the pattern was not consistent for males and females. Females showed no difference between skeletal and dental age while males showed significant skeletal retardation. This pattern of sex differences is consistent with that observed for modern living children and subadults experiencing nutritional stress. A comparison by cemetry also suggests a reduction in stress from early to late Christian times with later Christians showing a closer correspondence between skeletal and dental ages. While not statistically significant, this apparent reduction is consistent with previous research on the subadult remains.     

Implications of influence function analysis for sliced inverse regression and sliced average variance estimation

Sliced inverse regression, sliced inverse regression II andsliced average variance estimation are three related dimension-reductionmethods that require relatively mild model assumptions. As anapproximation for the relative influence of single observationsfrom large samples, the influence function is used to comparethe sensitivity of the three methods to particular observationaltypes. The analysis carried out here helps to explain why thereis a lack of agreement concerning the preferability of thesedimension-reduction procedures in general. An efficient sampleversion of the influence function is also developed and evaluated.     

Kinetic investigation of the functional role of phenylalanine-31 of recombinant human dihydrofolate reductase

The role of the active site residue phenylalanine-31 (Phe31) for recombinant human dihydrofolate reductase (rHDHFR) has been probed by comparing the kinetic behavior of wild-type enzyme (wt) with mutant in which Phe31 is replaced by leucine (F31L rHDHFR). At pH 7.65 the steady-state kcat is almost doubled, but the rate constant for hydride transfer is decreased to less than half that for wt enzyme, as is the rate of the obligatory isomerization of the substrate complex that precedes hydride transfer. Although steady-state measurements indicated that the mutation causes large increases in Km for both substrates, dissociation constants for many complexes are decreased. These apparent paradoxes are due to major mutation-induced decreases in rate constants (koff) for dissociation of folate, dihydrofolate, and tetrahydrofolate from all of their complexes. This results in a mechanism proceeding almost entirely by only one of the two pathways used by wt enzyme. Other consequences of these changes are a much altered dependence of steady-state kcat on pH, inhibition rather than activation by tetrahydrofolate, absence of hysteresis in transient-state kinetics, and a decrease in enzyme efficiency under physiological conditions. The results indicate that there is no quantitative correlation between dihydrofolate binding and the rate of hydride transfer for this enzyme.     

Down-regulation of Ia expression on macrophages by sea star factor

Sea star factor (SSF), a protein of 39,000 Da isolated from the coelomocytes of Asterias forbesi, was found to inhibit the induction of Ia expression on murine macrophages by concanavalin A supernatants. Addition of SSF to cultured macrophages at the same time as the lymphokine preparation significantly reduced the percentage Ia+ cells after 5 days culture, compared to cultures given lymphokine only. Intraperitoneal injection of SSF also reduced the percentage Ia+ peritoneal exudate macrophages by three-fourths in Listeria-infected mice. Addition of the cyclo-oxygenase inhibitor, indomethacin, to macrophage cultures reversed this Ia-suppressive effect of SSF. Since macrophages from endotoxin-unresponsive and endotoxin-responsive mice were both sensitive to the Ia-inhibitory effect of SSF, the induction of arachidonic acid metabolism and the inhibition of Ia appear to be independent of the action of endotoxin. The SSF-induced down regulation of Ia expression may be a major factor in the suppression of primary immune responses to T-dependent antigens previously noted in studies with SSF.     

Characterizing population vulnerability for 758 species

We investigate relationships between life history traits and the character of population dynamics as revealed by time series data. Our classification of time series is according to 'extinction category,' where we identify three classes of populations: (i) weakly varying populations with such high growth rates that long-term persistence is likely (unless some extreme catastrophe occurs); (ii) populations with such low growth rates that average population size must be large to buffer them against extinction in a variable environment; and (iii) highly variable populations that fluctuate so dramatically that dispersal or some other refuge mechanism is likely to be key to their avoidance of extinction. Using 1941 time series representing 758 species from the Global Population Dynamics Database, we find that, depending on the form of density dependence one assumes, between 46 and 90% of species exhibit dynamics that are so variable that even large carrying capacities could not buffer them against extinction on a 100-year time horizon. The fact that such a large proportion of population dynamics are so locally variable vindicates the growing realization that dispersal, habitat connectedness, and large-scale processes are key to local persistence. Furthermore, for mammals, simply by knowing body size, age at first reproduction, and average number of offspring we could correctly predict extinction categories for 83% of species (60 of 72).