Differential mitotic rates and patterns of growth in compartments in the Drosophila wing

In the wing disks of Drosophila slowly dividing cells of Minute mutations are progressively eliminated from Minute/Minute⁺ mosaic compartments by a process known as cell competition. From a study of two different Minutes we show here that the intensity of competition is greater in the more extreme Minute with the slowest rate of cell division. The way in which the more rapidly growing Minute⁺ clones grow and overcome the surrounding Minute cells is described and cell competition is shown to be a result of local interactions between slow- and faster-growing cells.     

Distribution of Polymorphus minutus among its intermediate hosts

Hirsch R. P. 1979. Distribution of Polymorphus minutus among its intermediate hosts. International journal for Parasitology10: 243–248. In 1971, Crofton investigated patterns of distribution of Polymorphus minutus in the intermediate host, Gammarus pulex. Among his conclusions were: (1) P. minutus populations occur in patterns similar to negative binomial distributions, and (2) parasite-induced host mortality results in patterns similar to truncated (high end) negative binomial distributions. Those conclusions, however, were not tested by statistical analyses. To test Crofton's observations, Chi-square goodness of fit tests were applied to data used by Crofton and an additional two stations sampled by Hynes & Nicholas in 1963. Analyses were expanded to include five theoretical distributions, four patterns of host mortality and various rates of host mortality. Truncated forms of negative binomial, positive binomial and Poisson distributions were also investigated where nontruncated distributions failed to fit observed distributions. It was found that negative binomial distributions most frequently describe patterns of P. minutus distribution with the exception of one population described by Poisson and another by positive binomial distributions. Crofton's assumption that truncated distributions result from parasite-induced host mortality seems unlikely in light of those analyses.     

Genetic variation in Cameroon: Thermostability variants of hemoglobin and of glucose-6-phosphate dehydrogenase

The technique of heat denaturation was used in addition to electrophoresis for the detection of thermostability variants of hemoglobin and glucose-6-phosphate dehydrogenase in an attempt to measure the amount of genetic variability present in villages in the United Republic of Cameroon, Equatorial Africa. A minimum of three to a maximum of 13 thermostability variants were estimated for HbA and HbS, and a minimum of two to a maximum of ten thermostability variants were estimated for GdA, GdB, and GdA —. It is suggested that hemoglobin and glucose-6-phosphate dehydrogenase thermostability variants are genetically determined and that the sites of these variants are at the hemoglobin and glucose-6-phosphate dehydrogenase structural loci. The evidence for the existence of these hidden variants and their importance in the neutralist v. selectionist controversy are discussed.This work was supported in part by National Institutes of Health Grant HL 16005. S. C. B. was an International Telephone and Telegraph International Fellow to Cameroon, was supported by Training Grant NIH-GM 07197, and is currently an Insurance Medical Scientist Scholar. This work is in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Genetics by S. C. B.     

The interaction of deoxyhemoglobin with the red cell membrane

The interaction of deoxyhemoglobin with the red cell membrane is characterized by comparing the affinity of deoxyhemoglobin for the membrane with that of oxyhemoglobin. The two techniques used, namely light scattering induced changes and quenching of the fluorescence intensity of a membrane embedded probe, demonstrate that deoxyhemoglobin exhibits a much lower affinity for the membrane than that of oxyhemoglobin. The binding constant of 2×10 M^?1 calculated for deoxyhemoglobin at 5 mM phosphate buffer and pH=6.0 is two orders of magnitude lower than the one calculated for oxyhemoglobin. It is estimated that under physiological conditions the only species capable of interacting with the membrane is the oxyhemoglobin.     

Preparation and conformational characterization of Cr(III) hemoglobin

Chromium(III) substituted hemoglobin has been prepared. Circular dichroism spectra in the UV region have been recorded in the presence and absence of the allosteric affector inositol hexaphosphate. The reactivity with bromthymol blue and p-mercuribenzoate has been measured. All data indicate a T state (or T state-like) structure, whereas an R structure would be expected from the chromium stereochemistry. Similarities to cobalt(III) hemoglobin suggest that the chromium derivative also exists as an internal hemichrome. Thus, despite major tertiary structure differences, “denatured” hemichromes may have a quaternary structure quite similar to deoxyhemoglobin.     

Replication of ultraviolet-irradiated simian virus 40 in monkey kidney cells

This paper extends the concepts of linkage and control, previously studied in single phase allosteric and polysteric systems, to multiple phase (polyphasic) systems. In particular, a study has been made of the dependence of the solubility of sickle cell hemoglobin on oxygen partial pressure. Phase diagrams are obtained from observations of birefringence changes of hemoglobin solutions in a thin film optical cell. The effects of temperature and pH are found to be correlated largely with oxygen binding curves for non-gelling solutions. This suggests only small enthalpy and proton release changes for the gelation process. Variable time delays for the onset of birefringence were observed for partial deoxygenation of a fully oxygenated sample. The reciprocal of the time delay depends on a high power of the supersaturation ratio. The nucleation kinetics are, thereby, similar to those found in fully deoxygenated solutions in temperature-jump studies. Oxygen binding curves for non-gelling solutions of sickle cell hemoglobin were used in conjunction with the phase diagram results to evaluate oxygen binding curves for the polymer gel. Account was taken of the water content of the gel and of the large non-ideality of the solution. Analysis of the phase diagram data based on polyphasic linkage relationships suggests that some reversible oxygen-binding by the gel is present. The difference in oxygen binding between solution and gel obtained in this way is similar to that found by Hofrichter (1979) for carbon monoxide.     

Plasmodium falciparum: physiological interactions with the human sickle cell.

The malaria parasite, Plasmodium falciparum, enhances the rate and extent of sickling of infected hemoglobin S heterozygous human erythrocytes. Upon sickling of the host cell, the parasite is killed. Parasite-free lysates of highly infected cells were analyzed to determine the mechanism by which sickling is enhanced. The intraerythrocytic pH of the infected cell was estimated to be 0.4 units below that of the uninfected cell, a difference which could result in a 20-fold increase in the extent of sickling under physiological conditions. Sickle-cell hemoglobin (HbS) heterozygous (AS) erythrocytes had decreased intracellular potassium after 24 hr of culture under conditions which cause sickling and parasite death. When infected AS cells were cultured in high-potassium medium under these conditions the parasites were protected. The medium did not prevent sickling but did maintain normal intracellular potassium levels. It is suggested that sequestration of trophozoite-infected AS cells in the venules leads to the sickling of the host cell, loss of erythrocytic potassium, and parasite death. The resulting attenuation of parasite multiplication would favor the survival of the HbS heterozygote and maintain the HbS gene at high frequencies in areas endemic for falciparum malaria.     

Proliferation and morphology of chick embryo cells cultured in the presence of horse serum and hemoglobin

Summary We have shown previously that hemoglobin greatly stimulates chick embryo cell proliferation in Eagle's minimal essential medium supplemented with horse serum. In the present study we compared the effects of horse serum plus 10 μM hemoglobin to those of fetal bovine serum on subcultures of chick embryo cells serially propagated at high cell densities. The cells became elongated in the presence of fetal bovine serum and their rate of proliferation progressively decreased, whereas they became polygonal in the presence of horse serum plus hemoglobin and proliferated well in successive cell passages. The polygonal cell obtained in the presence of horse serum plus hemoglobin rapidly elongated if cultured at low cell densities in the presence of fetal bovine serum, but, in contrast, elongated cells did not yield polygonal cells if cultured at low densities in the presence of horse serum plus hemoglobin. It is possible that the polygonal and elongated cells are undifferentiated cells and differentiating myogenic cells, respectively.     

Two-nucleotide codon change in a hemoglobin polymorphism of the Celebes black ape (Macaca nigra)

A hemoglobin polymorphism involving variant -chains was demonstrated in the Celebes black ape, Macaca nigra. Fingerprinting and amino acid analysis of the tryptic peptides from the two chain types have shown that they differ by a single amino acid substitution, between lysine and aspartic acid, which requires a two-nucleotide change in the corresponding codon. Another substitution in the same codon is found as a species difference between the black ape -chain and that of other macaques.