Biomedical subjects
A A Teleman
Publications and source records attributed to A A Teleman.
Dpp gradient formation in the Drosophila wing imaginal disc.
The secreted signaling protein Dpp acts as a morphogen to pattern the anterior-posterior axis of the Drosophila wing. Dpp activity is required in all cells of the developing wing imaginal disc, but the ligand gradient that supports this activity has not been characterized. Here we make use of a biologically active form of Dpp tagged with GFP to examine the ligand gradient. Dpp-GFP forms an unstable extracellular gradient that spreads rapidly in the wing disc. The activity gradient visualized by MAD phosphorylation differs in shape from the ligand gradient. The pMAD gradient adjusted to compartment size when this was experimentally altered. These observations suggest that the Dpp activity gradient may be shaped at the level of receptor activation.
Chromosome arrangement within a bacterium.
BACKGROUND: The contour length of the circular chromosome of bacteria is greater than a millimeter but must be accommodated within a cell that is only a few micrometers in length. Bacteria do not have nucleosomes and little is known about the arrangement of the chromosome inside a prokaryotic cell. RESULTS: We have investigated the arrangement of chromosomal DNA within the bacterium Bacillus subtilis by using fluorescence microscopy to visualize two sites on the chromosome simultaneously in the same cell. Indirect immunofluorescence with antibodies against the chromosome partition protein Spo0J were used to visualize the replication origin region of the chromosome. Green fluorescent protein fused to the lactose operon repressor Lacl was used to decorate tandem copies of the lactose operon operator lacO. A cassette of tandem operators was separately inserted into the chromosome near the origin (359 degrees), near the replication terminus (181 degrees), or at two points in between (90 degrees and 270 degrees). The results show that the layout of the chromosome is dynamic but is principally arranged with the origin and terminus maximally apart and the quarter points of the chromosome in between. CONCLUSIONS: The use of cytological methods to visualize two chromosomal sites in the same cell has provided a glimpse of the arrangement of a bacterial chromosome. We conclude that, to a first approximation, the folding of the bacterial chromosome is consistent with, and may preserve, the linear order of genes on the DNA.
Use of time-lapse microscopy to visualize rapid movement of the replication origin region of the chromosome during the cell cycle in Bacillus subtilis.
We describe the use of time-lapse fluorescence microscopy to visualize the movement of the DNA replication origin and terminus regions on the Bacillus subtilis chromosome during the course of the cell cycle. The origin and terminus regions were tagged with a cassette of tandem lac operator repeats and visualized through the use of a fusion of the green fluorescent protein to the LacI repressor. We have discovered that origin regions abruptly move apart towards the cell poles during a brief interval of the cell cycle. This movement was also seen in the absence of cell wall growth and in the absence of the product of the parB homologue spo0J. The origin regions moved apart an average distance of 1.4 microm in an 11 min period of abrupt movement, representing an average velocity of 0.17 microm min(-1), and reaching a maximum velocity of greater than 0.27 microm min(-1). The terminus region also exhibited a striking pattern of movement but not as far or a rapid as the origin region. These results provide evidence for a mitotic-like motor that is responsible for segregation of the origin regions of the chromosomes.