Loss of heterozygosity in tumor cells requires re-evaluation: the data are biased by the size-dependent differential sensitivity of allele detection

Normal tissue contamination of tumors may eclipse the detection of loss of heterozygosity (LOH) by microsatellite analysis and may also hamper isolation of tumor suppressor genes. To test the potential impact of this problem, we prepared artificial mixtures of mouse-human microcell hybrid lines that carried different alleles of the same chromosome 3 marker. After performing an allele titration assay, we found a consistent difference between the LOH of a high molecular weight (H) allele and the LOH of a low molecular weight (L) allele of the same CA repeat marker. It follows that normal tissue admixtures will be less of a problem when LOH affects a H allele than with a L allele. Random screening of 100 papers published between 1994 and 1999 revealed that the loss of a L allele was recorded at about half the frequency (52%) of loss of a H allele. To avoid this bias, we have developed rules for the evaluation of LOH data. We suggest that the loss of a L allele should be given more weight than the loss of a H allele in LOH studies using microsatellite markers.     

Relationships between basic life history parameters and population size

We consider an ideal population with a stable age composition changing according Lotka equation. Additional assumptions are made concerning the constancy of population size, independence of specific mortality rate on age, and linear dependence of female fecundity on its weight. A relationship has been obtained [formula: see text] where N0 is initial numbers of a generation, N[alpha, omega] is total numbers of the mature part of the population, w[alpha, omega] is a mean weight of a mature individual, s is sex ratio, c is specific fecundity (per unit of weight) and l0 is the probability of larval surviving. The growth of an individual is described by the Bertalanffy function. Methods of calculation of life history parameters are discussed. A method is proposed to calculate the age of maturity (alpha) and at the end (omega) of the reproduction period as first and second inflection points of the growth rate curve. Based upon data on development of 27 populations of several species of fishes of inland waters of Russia the following relationship have been obtained: [formula: see text] for populations with [formula: see text] < or = 100 g, [formula: see text] for populations with [formula: see text] > 100 g, and [formula: see text] for all populations.     

Fluorimetric study of phospholipase A-induced efflux of Ca2+ from liposomes]

Artificial vesicles, liposomes, were prepared from the total fraction of phospholipids of rat liver mitochondria. Electron microscopy showed that the structure of liposomes depended on cation composition of the medium in which they were formed. Fluorescence of chlorotetracycline increased in the suspension of liposomes loaded with Ca+2 due to the formation of Ca+2-chlorotetracycline-phospholipid membrane complex. Incubation of liposome suspension with phospholipase A in the presence of EDTA resulted in a decrease of chlorotetracycline fluorescence indicating a break of the integrity of liposome membranes and Ca+2 efflux.