A cellular model for drug interactions on hematopoiesis: The use of human umbilical cord blood progenitors as a model for the study of drug-related myelosuppression of normal hematopoiesis

A cellular model of hematopoiesis which would be more convenient than bone marrow (BM) progenitors and directly relevant to human pathology is needed in order to investigate xenobiotic toxicity. Human umbilical cord blood (HCB), previously shown to be able to repopulate BM, provides a powerful in vitro model of normal human hematopoiesis. In order to validate the use of normal HCB progenitors as targets for dose-related myelosuppression, we used clonogenic assays and expansion in a liquid culture of progenitor-enriched cell suspensions from HCB. A series of 8 reference molecules, doxorubicin, cytosine-arabinoside, 5-fluorouracil, 3-azido-3-deoxythymidine, acetylsalicyclic acid, sodium valproate and two cephalosporin antibiotics, were tested. In vitro 50% inhibition concentrations (IC₅₀) were compared to those observed or reported with BM progenitors, and to the values of plasma concentrations from treated patients. HCB progenitors as in vitro targets for cytotoxic molecules were easy to access and handle, and their use was sensitive, specific and reproducible. They gave results similar to BM progenitors and allowed a qualitative approach to cellular metabolism and toxicity using morphological, flow cytometric and chromatographic methods.Abbreviations ARA-CC cytosine arabinoside - AS acetylsalicylic acid - AZTT 3-azido-3-deoxythymidine - BFUU burst-forming units - BM bone marrow - CFU colony-forming units - DOXX doxorubicin - FU 5-fluorouracil - glyAA glyAcophorin A - HCB human umbilical cord blood - IU international units - PCMEM human placenta-conditioned medium - VA sodium valproate     

Characteristics of lactococci cultures produced in commercial media

Strains ofLactococcus lactis ssplactis andL. lactis sspcremoris were propagated on milk, three commercial highly buffered media (HB media), and four commercial media designed for external pH control (EC media). With milk and HB media, fermentation was allowed to proceed until a pH of 4.9 was reached. With EC media, pH was maintained at 6.0 with 5 N NH₄OH. The cultures were analyzed for chain length, viable population, specific acidifying activity (SAA) and specific proteolytic activity (SPA). The starters were stored at 4° C for 3 days, and analyses for chain length, viable population and SAA were repeated. It was more difficult to standardize medium composition with the rehydrated commercial blends, as their titratable acidities had greater proportional variations than milk. As a rule, chain length was longer in fresh cultures than in the stored starters, andL. lactis sppcremoris cultures had longer chains thanL. lactis ssplactis. All commercial media produced starters with total populations at least as high as that obtained in milk. With the EC media, populations could be five times greater than with milk; increases were less important in HB media. The increase in population in EC and HB media was more marked withL. lactis ssplactis than forL. lactis sspcremoris strains. Storage at 4° C for 3 days did not significantly reduceL. lactis populations, but mortality (up to 70%) was observed withL. lactis sspcremoris. The overall SAA ofL. lactis ssplactis cultures in EC media was 35% lower than milk- or HB media-grown starters, but the greater populations reached in EC media enabled a significant reduction in inoculation rate. Some statistically significant correlations were obtained between SAA and SPA (positive) as well as with chain length (negative), but the coefficients of determination were generally very low. The drop in pH during storage at 4° C was less with HB media than in milk, and was in relation to their buffering capacity.     

Kinetics of leucrose formation from sucrose by dextransucrase

Leucrose formation from sucrose and fructose by dextransucrase is of practical interest. It has been investigated at different experimental conditions, including the influence of temperature on reaction rate and selectivity. Under appropriate conditions high product yield can be obtained. Furthermore, a model is presented that allows interpretation of the experimental data.     

Tropical tree species diversity: a test of the Janzen-Connell model

To test the premises and predictions of the Janzen-Connell model (Janzen's spacing mechanism), seeds of the rainforest canopy tree, Brosimum alicastrum, were placed at different distances from the parent tree and their removal observed over 3 weeks. The number and density of naturally occurring seeds at different distances from the parent tree were also estimated. Predation was not greater near the parent tree, except on the very small spatial scale: the proportion of experimental seeds removed was greater 1 m from the trunk than it was 5–25 m from the trunk. Predation was negatively correlated with seed density, not positively as the Janzen-Connell model assumes-presumably due to predator satiation. The density of seeds after predation peaked 5 m from the tree trunk, but this is well within the crown radius of the parent tree. There is a peak in the number of potential recruits at a distance of 10 m from the parent tree, due to the peaked initial distribution of seeds. This peak is caused by the interaction between the seed density curve and the increasing area of an annulus around the parent tree at increasing distances, not by the product of the density curve and the predation curve. However, it is important to realize that it is not the presence of a peak in recruitment away from the parent that is essential to maintaining tropical tree species diversity, but frequency-dependent recruitment induced by poor recruitment near conspecifics. Predator satiation seems to be an important factor in the survival of B. alicastrum seeds, possibly at several spatial scales. The number of seeds produced by the tree is negatively correlated with the loss to predators, and trees that have a fruiting conspecific nearby also suffer lower levels of predation. Seed predation increases as one moves from the forest edge into the interior, creating an edge effect that may have long-term effects on the forest composition and tree species diversity. More studies are needed, for other species, other localities, and larger spatial and temporal scales, on both the Janzen-Connell mechanism and this edge effect.     

Wild pearl millet population (Pennisetum glaucum,Poaceae) integrity in agricultural Sahelian areas. An example from Keita (Niger)

Morphometric and isozymic analyses of adjacent cultivated and spontaneous populations of pearl millet in Niger revealed in the field a unique continuous distribution of phenotypes ranging from the most cultivated one to a typical cultivated × wild hybrid. The natural population was subdivided into a major wild group and a hybrid wild × cultivated group. Cultivated millet displayed an equilibrium state between recombined domesticated and wild genes. The natural population, in spite of a high rate of immigration by pollen from cultivated plants, retained its structure by apparently reproducing itself exclusively from the major wild group.     

Brood size and the cost of provisioning nestlings: interpreting Lack's hypothesis

A recent model of parental provisioning (the tradeoff model) suggests that the maximum delivery rate of food to nestlings represents a tradeoff between parental residual reproductive value and nestling survival. In contrast, Lack's hypothesis suggests that maximum provisioning rate determines brood size and therefore delivery rates are limited by shortages of food or foraging time, not by tradeoffs of parental investment. Several authors have examined the shape of the per-nestling feeding curves to test the tradeoff model against Lack's hypothesis. We show that Lack's hypothesis can produce per-nestling feeding curves consistent with the tradeoff model. Therefore, the shape of the per-nestling feeding curve cannot be used to distinguish between the models.     

Annual survival rate and age structure of habu,Trimeresurus flavoviridis (Viperidae), on Minna island,Japan: Estimation from removal trapping

A population of a viperid snake,Trimeresurus flavoviridis, was studied over 10 years by removal trapping on a small subtropical island in Japan. The sex ratio of trapped individuals changed seasonally, but was not biased to either sex in the whole sample of 258 individuals. The age of each individual was estimated through the size structure and the age-size relationship. The minimum number of individuals at the beginning of the study was estimated through accumulating older individuals trapped in the subsequent years. By assuming an annual natural survival rate in the course of this accumulation, an age structure was simulated which led to calculate a resulted natural survival rate. The assumed rate of 0.62 fitted best to the resulted one. The annual trapped proportion estimated on the simulated absolute number of individuals was higher in older individuals than in younger ones with the overall mean of 16%.     

Time and biosequences

In this paper we discuss and demonstrate the importance of several factors relative to the relationship between time and evolution of biosequences. In both quantitative and qualitative measurements of the genetic distances, the compositional constraints of the nucleotide sequences play a very important role. We demonstrate that when homologous sequences significantly differ in base composition we get erratic branching order and/or wrong evaluation of the evolutionary rates. We must consider that every gene may have a different evolutionary dynamic along its sequence, generally linked to its functional constraints; this too can seriously affect its clocklike behavior. We report some cases showing how these factors can affect the quantitative measurements of the genetic distances of biosequences. Presented at the NATO Advanced Research Workshop onGenome Organization and Evolution, Spetsai, Greece, 16–22 September 1992     

PEAK SHIFTS AND POLYMORPHISM DURING PHASE THREE OF WRIGHT'S SHIFTING-BALANCE PROCESS

The third phase of Wright's shifting-balance theory involves the export of adaptive gene combinations from one subpopulation to another. Previous results have demonstrated that this can occur at very low migration rates, but it has been argued that this simply reflects the ability of migration to overcome selection and fix any (even deleterious) alleles. Here, previous analyses are extended by concentrating on the critical balance between forward and reverse migration rates that still allows phase III to proceed. It is shown that selective advantage, dominance, recombination rate, and the number of loci all affect the ability of a genotype to invade and become fixed in a new subpopulation, but it is unlikely that phase III will occur in the absence of differential migration unless the invading genotype consists of a few dominant loci with a large selection advantage, spreading into a few populations of lower fitness. Therefore, as was envisioned by Wright, differential migration from more to less fit populations will be necessary for phase III to occur under most circumstances.     

Geographic differences in Blainville's beaked whale (Mesoplodon densirostris) echolocation clicks

Aim

Understanding cetacean species' distributions and population structure over space and time is necessary for effective conservation and management. Geographic differences in acoustic signals may provide a line of evidence for population-level discrimination in some cetacean species. We use acoustic recordings collected over broad spatial and temporal scales to investigate whether global variability in echolocation click peak frequency could elucidate population structure in Blainville's beaked whale (Mesoplodon densirostris), a cryptic species well-studied acoustically.

Location

North Pacific, Western North Atlantic and Gulf of Mexico.

Time period

2004–2021.

Major taxa studied

Blainville's beaked whale.

Methods

Passive acoustic data were collected at 76 sites and 150 cumulative years of data were analysed to extract beaked whale echolocation clicks. Using an automated detector and subsequent weighted network clustering on spectral content and interclick interval of clicks, we determined the properties of a primary cluster of clicks with similar characteristics per site. These were compared within regions and across ocean basins and evaluated for suitability as population-level indicators.

Results

Spectral averages obtained from primary clusters of echolocation clicks identified at each site were similar in overall shape but varied in peak frequency by up to 8 kHz. We identified a latitudinal cline, with higher peak frequencies occurring in lower latitudes.

Main conclusions

It may be possible to acoustically delineate populations of Blainville's beaked whales. The documented negative correlation between signal peak frequency and latitude could relate to body size. Body size has been shown to influence signal frequency, with lower frequencies produced by larger animals, which are subsequently more common in higher latitudes for some species, although data are lacking to adequately investigate this for beaked whales. Prey size and depth may shape frequency content of echolocation signals, and larger prey items may occur in higher latitudes, resulting in lower signal frequencies of their predators.