Chromosomal alterations and DNA content in rats during ageing

Chromosome analysis of bone marrow cells from 96 sex-matched Rattus norvegicus of 12 different age groups showed a significant increase in hypodiploid cells with ageing. However, in meiotic preparations from gonadal cells of male rats the frequency of hypodiploid or hyperdiploid cells did not change significantly. In situ DNA estimation of bone marrow nuclei, following Feulgen cytophotometry, also did not show any significant difference with gradual age changes.Key words: senescence, DNA content, age-related changes.

A different level of X-chromosomal transcription in an In(1)BM2 (reinverted) strain and in its hyperploid derivatives resolves an X-coded regulatory activity for dosage compensation in Drosophila

SummaryThe transcriptional competence of the X-chromosome of a mutant strain of Drosophila melanogaster, [in(1)BM2 (reinverted)], and of hyperploid derivatives with different additional segments of the X-chromosome has been examined. The single X in the mutant male shows twice as much puffiness and RNA synthesis as does that in the normal male, revealing a level of X-coded activity in addition to the normal male and female levels. Feulgen cytophotometry reveals no duplication of DNA content in the mutant X. When duplication for the segments 1A-3E, 9A-20F, 11A-20F and 16A-20F of the X-chromosome are combined in the male with the mutant chromosome, the super-hyperactivity of the mutant X is completely abolished. In combination with the Bs. Y duplication, which contains 16A7-B2, the two-fold activity is also completely suppressed.The mutant chromosome can appear in three discrete manifestations, namely, highly flabby, intermittently flabby and normal, suggesting a leaky nature of the mutant. The effect is also temperature-sensitive. Our results suggest that there may be a modulator gene complex (M+) in the 16A7-B2 region as well as regulators elsewhere on the X, which in combination influence the hyperactivity of the male X in Drosophila. We suggest that the In(1)BM2 (reinverted) chromosome carries a hypomorphic mutation of M+(Mm). The results presented here and earlier data on various X-chromosomal and autosomal hyperploids are discussed in the light of a model for dosage compensation in Drosophila.

Applications of microcomputer technology to cytophotometry.

Lack of appropriate software support for microprocessor program development has previously limited the applications of such technology in the field of microspectrophotometry. This paper describes our use of a Vickers M86 integrating microdensitometer coupled through a custom-designed interface circuit to a Processor Technology SOL III microcomputer. W e have developed a series of interactive, user-oriented programs for DNA-Feulgen cytophotometry with this instrument to allow automatic storage of data in files on floppy disks and instant retrieval of sets of measurements for statistical processing. The same data files can also be used to generate graphic displays in the form of bar histograms or plots of linear regressions on a video monitor and to produce hardcopy output of data files and graphic displays through the use of a high speed DIABLO printer.

The occurrence of nuclear fusion in the amoebal phase of the slime mold Echinostelium minutum: a reinterpretation of the significance of this phenomenon

Nuclear fusion occurs in less than 1% of the myxamoebae of Echinostelium minutum de Bary, isolate D-3, sublines 1965 and 1971. Binucleate amoebae undergo synchronous mitosis, the two nuclei fuse, the fusion nucleus divides, cytokinesis occurs, and uninucleate daughter cells are formed. Failure to find a haploid–diploid alternance between the amoebal and plasmodial phases using Feulgen cytophotometry suggests that nuclear fusion is not a prerequisite for plasmodial formation in this isolate. Nuclear fusion may be one of the mechanisms which has led to the polyploid condition of the 1971 subline. This phenomenon may also represent a parasexual process.