Biomedical subjects

Burnley Jaklevic

Publications and source records attributed to Burnley Jaklevic.

5 recordsLinked to original sources

PubMed2006

Drosophila ATR in double-strand break repair.

The ability of a cell to sense and respond to DNA damage is essential for genome stability. An important aspect of the response is arrest of the cell cycle, presumably to allow time for repair. Ataxia telangiectasia mutated (ATM) and ATR are essential for such cell-cycle control, but some observations suggest that they also play a direct role in DNA repair. The Drosophila ortholog of ATR, MEI-41, mediates the DNA damage-dependent G2-M checkpoint. We examined the role of MEI-41 in repair of double-strand breaks (DSBs) induced by P-element excision. We found that mei-41 mutants are defective in completing the later steps of homologous recombination repair, but have no defects in end-joining repair. We hypothesized that these repair defects are the result of loss of checkpoint control. To test this, we genetically reduced mitotic cyclin levels and also examined repair in grp (DmChk1) and lok (DmChk2) mutants. Our results suggest that a significant component of the repair defects is due to loss of MEI-41-dependent cell cycle regulation. However, this does not account for all of the defects we observed. We propose a novel role for MEI-41 in DSB repair, independent of the Chk1/Chk2-mediated checkpoint response.

Animals↗

PubMed2006

Contribution of growth and cell cycle checkpoints to radiation survival in Drosophila.

Cell cycle checkpoints contribute to survival after exposure to ionizing radiation (IR) by arresting the cell cycle and permitting repair. As such, yeast and mammalian cells lacking checkpoints are more sensitive to killing by IR. We reported previously that Drosophila larvae mutant for grp (encoding a homolog of Chk1) survive IR as well as wild type despite being deficient in cell cycle checkpoints. This discrepancy could be due to differences either among species or between unicellular and multicellular systems. Here, we provide evidence that Grapes is needed for survival of Drosophila S2 cells after exposure to similar doses of IR, suggesting that multicellular organisms may utilize checkpoint-independent mechanisms to survive irradiation. The dispensability of checkpoints in multicellular organisms could be due to replacement of damaged cells by regeneration through increased nutritional uptake and compensatory proliferation. In support of this idea, we find that inhibition of nutritional uptake (by starvation or onset of pupariation) or inhibition of growth factor signaling and downstream targets (by mutations in cdk4, chico, or dmyc) reduced the radiation survival of larvae. Further, some of these treatments are more detrimental for grp mutants, suggesting that the need for compensatory proliferation is greater for checkpoint mutants. The difference in survival of grp and wild-type larvae allowed us to screen for small molecules that act as genotype-specific radiation sensitizers in a multicellular context. A pilot screen of a small molecule library from the National Cancer Institute yielded known and approved radio-sensitizing anticancer drugs. Since radiation is a common treatment option for human cancers, we propose that Drosophila may be used as an in vivo screening tool for genotype-specific drugs that enhance the effect of radiation therapy.

Animals↗

PubMed2006

Ionizing radiation induces caspase-dependent but Chk2- and p53-independent cell death in Drosophila melanogaster.

Ionizing radiation (IR) can induce apoptosis via p53, which is the most commonly mutated gene in human cancers. Loss of p53, however, can render cancer cells refractory to therapeutic effects of IR. Alternate p53-independent pathways exist but are not as well understood as p53-dependent apoptosis. Studies of how IR induces p53-independent cell death could benefit from the existence of a genetically tractable model. In Drosophila melanogaster, IR induces apoptosis in the imaginal discs of larvae, typically assayed at 4-6 hr after exposure to a LD(50) dose. In mutants of Drosophila Chk2 or p53 homologs, apoptosis is severely diminished in these assays, leading to the widely held belief that IR-induced apoptosis depends on these genes in Drosophila. In this article, we show that IR-induced apoptosis still occurs in the imaginal discs of chk2 and p53 mutant larvae, albeit with a delay. We demonstrate that this phenomenon is a true apoptotic response because it requires caspase activity and the chromosomal locus that encodes the pro-apoptotic genes reaper, hid, and grim. We also show that Chk2- and p53-independent apoptosis is IR dose-dependent and is therefore probably triggered by a DNA damage signal. We conclude that Drosophila has Chk2- and p53-independent pathways to activate caspases and induce apoptosis in response to IR. This work establishes Drosophila as a model for p53-independent apoptosis, which is of potential therapeutic importance for inducing cell death in p53-deficient cancer cells.

Animals↗

PubMed2004

Control of mitotic entry after DNA damage in Drosophila.

In the presence of DNA damage, cells delay the entry into mitosis, presumably to allow time for repair. Methods to detect the delay of mitosis in a multicellular model organism, Drosophila melanogaster, are described here. These include the collection of embryos and larvae, irradiation with x-rays to damage DNA, and fixing and staining of tissues with an antibody to phosphorylated histone H3 to measure the mitotic index. These methods should be useful in identifying potential mutants that are unable to regulate mitosis following DNA damage.

Animals↗

PubMed2003

Cell turnover: flexible coupling meets the needs of development.

The identification of Drosophila genes that inhibit proliferation while simultaneously promoting apoptosis--decreasing cell number--or that promote proliferation while simultaneously inhibiting apoptosis--increasing cell number--has revealed new ways that cell birth and death may be coupled to meet the needs of development.

Animals↗