Morphological characteristics of Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju in laboratory cultures.

The freshwater cyanoprokaryote Cylindrospermopsis raciborskii has become increasingly prevalent in tropical and temperate water bodies worldwide. The morphological characteristics of this species were investigated under different growth rates in continuous cultures (at steady state) and in batch (phosphorus starved) cultures with different mineral nitrogen forms. The species displays an enormous morphological variability under controlled condition. The occurrence of extreme long twisted filaments was found near the maximum growth rate and under high ammonium concentration. Rarely the heterocytes of Cylindrospermopsis raciborskii arise intercalarly between two neighbouring cells(i.e. intercalary heterocytes were found). The morphological features are highly effected by environmental conditions and nutrient availability. Under P-starvation extreme morphology appeared. The specifications of C. africana and C. cuspis overlap with that of C. raciborskii accordingly this is not clear characteristic feature to distinguish species. A pure culture of a pro- or eukaryote alga growing in continuous cultures is a good method for giving a suitable overview on all morphological possibilities of a tested organism.

Recombinant human interferon beta ser protects against zidovudine-induced genetic damage in AIDS patients.

This study was conducted to evaluate the in vivo genotoxicity of zidovudine (ZDV) in patients with Acquired Immune Deficiency Syndrome (AIDS). Patients with this disease who were non-smokers and on ZDV (1200 mg/day) as their only medication for 4 weeks to 7 months were studied. Patients with AIDS who had not received ZDV served as a negative control. Whole blood cultures were initiated by conventional methods with PHA 1:50 dilution. In addition, for each culture there was an untreated control and a recombinant interferon-beta (rIFN-beta)-treated culture. The IFN-treated cultures were exposed to 10, 100, 1000, or 10000 units of rIFN-beta for the entire incubation period. The cells were harvested at 72 h and stained with a fluorescence plus Giemsa method which permits the determination of the number of division cycles a cell has completed. One hundred metaphases from first division cells were scored from each culture for chromosome aberrations that were mainly from the chromatid-type, i.e. chromatid, chromosome, and isochromatid breaks. The frequency of breaks in the ZDV and no ZDV group was 8.29 +/- 2.65 and 0.5 +/- 0.29 per 100 cells respectively (P less than 0.05). Cultures from ZDV patients that were incubated with 100 and 1000 units of rIFN-beta, however, showed a frequency of 1.3 +/- 0.71 and 1.9 +/- 1.08 respectively, which was significantly lower than observed in the cultures not exposed to IFN (P less than 0.05). At the highest dose of rIFN-beta utilized no aberrations were detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of X-ray-induced chromosome breakpoints in Down syndrome lymphocytes.

Down syndrome (DS) individuals are known to be predisposed to develop leukemia and their lymphocytes are highly sensitive to the induction of chromosome aberrations by X-rays. A study was conducted to identify the chromosome breakpoints and to evaluate whether site specificity for chromosome breakage and rearrangement may exist which may explain the predisposition phenomenon. DS lymphocytes at the G1 phase of the cell cycle were irradiated with 300, 450, and 600 rad of X-rays. Cells were harvested after 3 days in culture and 193 G-banded karyotypes were analyzed to identify the induced chromosome abnormalities. Out of 273 breakpoints identified, 122 were involved in the formation of stable chromosome rearrangements and 151 in the formation of unstable abnormalities. The Poisson analysis of these breakpoints demonstrated that 16 chromosome bands located in chromosomes 1, 3, 7, 12, 17, 19 and X were preferentially involved in breakage and rearrangement (P less than 0.05). These 16 bands are also found to be locations of "cancer breakpoints," oncogenes, or fragile sites. Many abnormal cells were observed to carry stable chromosome rearrangements only. Therefore, these cells are presumed to be compatible with survival and to be "initiated" in the transformation process. We propose that similar stable and site-specific chromosome rearrangements may exist in proliferating cells in DS individuals after exposure to clastogens and that this abnormality predisposes them to develop leukemia.

Chromosomal radiosensitivity of Down syndrome lymphocytes at different stages of the cell cycle.

Down syndrome (DS) is one of the most common types of congenital anomalies. In addition to a wide spectrum of developmental abnormalities, DS patients are also highly sensitive to the induction of chromosomal aberrations when their GO lymphocytes are exposed to ionizing radiation. We conducted the present study to evaluate the effect of X-rays on proliferating lymphocytes from DS and normal individuals. We found that DS lymphocytes were significantly more sensitive to X-ray induction of chromosome aberrations than normal cells, when they were irradiated at the G0, G1 and S phases of the cell cycle. The S phase was the most radiosensitive phase and would lead to extensive cell killing, whereas the G1 phase seemed to be more prone to the induction of chromosome rearrangements that would potentially lead to serious long-term consequences.