ABSTRACT
The Sn locus of maize is functionally similar to the R and B loci, in that Sn differentially controls the tissue-specific deposition of anthocyanin pigments in certain seedling and plant cells. We show that Sn shows molecular similarity to the R gene and have used R DNA probes to characterize several Sn alleles. Northern analysis demonstrates that all Sn alleles encode a 2.5 kb transcript, which is expressed in a tissue-specific fashion consistent with the distribution of anthocyanins. Expression of the Sn gene is light-regulated. However, the Sn: bol3 allele allows Sn mRNA transcription to occur in the dark, leading to pigmentation in dark-grown seedlings and cob integuments. We report the isolation of genomic and cDNA clones of the light-independent Sn: bol3 allele. Using Sn cDNA as a probe, the spatial and temporal expression of Sn has been examined. The cell-specific localization of Sn mRNA has been confirmed by in situ hybridization using labelled antisense RNA probes. According to its proposed regulatory role, expression of Sn precedes and, in turn, causes a coordinate and tissue-specific accumulation of mRNA of structural genes for pigment synthesis and deposition, such as A1 and C2. The functional and structural relationship between R, B, Lc and Sn is discussed in terms of an evolutionary derivation from a single ancestral gene which gave rise this diverse gene family by successive duplication events.
Subject(s)
Genes, Regulator , Zea mays/genetics , Acyltransferases/genetics , Alcohol Oxidoreductases/genetics , Alleles , Anthocyanins/genetics , Blotting, Northern , Blotting, Southern , Cloning, Molecular , DNA , Gene Expression Regulation , Genes, Plant , Genes, Regulator/radiation effects , Light , Nucleic Acid Hybridization , Polymorphism, Restriction Fragment Length , Restriction Mapping , Sequence Homology, Nucleic Acid , Transcription, GeneticABSTRACT
In Drosophila melanogaster cell lines and larval neuroblast cells, two aspects of the phenomenon of sister chromatid exchanges were analyzed: (1) the frequency of SCEs in relation to the ploidy level (comparing diploid and tetraploid cells) and in relation to the cell type (comparing embryonic and larval cells) (2) the localization of the sites of exchange with reference to eu- and heterochromatin. A good correlation between SCE frequency and genome size in the same cell type (in distant species also), but a significant difference in the SCE rate between different cell types within the same species, were found. The results confirmed also the non-random distribution of SCEs in the different portions of the genome since a preferential localization in the euchromatin was clearly demonstrated. Moreover, a direct proportionality between SCE frequency and the length of the S phase was supposed, favouring the hypothesis of a relationship between the phenomenon of sister chromatid exchanges and DNA replication.
Subject(s)
Crossing Over, Genetic , DNA Replication , Drosophila melanogaster/genetics , Sister Chromatid Exchange , Animals , Cell Line , Chromosomes/ultrastructure , Embryo, Nonmammalian , Karyotyping , Larva , PloidiesSubject(s)
Cell Line , Chromosome Aberrations , Chromosomes , Animals , Chromosome Banding , Chromosome Deletion , Chromosomes/ultrastructure , Drosophila melanogaster , Female , Genes , Karyotyping , Male , Mutation , Ploidies , Translocation, Genetic , X Chromosome , Y ChromosomeABSTRACT
The chromosomal changes occurred in two independent cell lines (GM2 and GM3) of Drosophila melanogaster maintained in medium supplemented with serum and in serum-free medium were compared. In both culture conditions and in both lines a chromosomal evolution was revealed. Structural and numerical variations were analysed. The breaks giving rise to rearrangements were at heterochromatic level. Moreover, a tetraploidisation followed by loss of chromosomes or of portions of chromosomes recalls an analogous cycle observed in human cells.
