Association between sister chromatids is essential for their attachment and segregation to opposite poles of the spindle in mitosis and meiosis II. Sister‐chromatid cohesion is also likely to be involved in linking homologous chromosomes together in meiosis I. Cytological observations provide evidence that attachment between sister chromatids is different in meiosis and mitosis and suggest that cohesion between the chromatid arms may differ mechanistically from that at the centromere. The physical nature of cohesion is addressed, and proteins that are candidates (...) for holding sister chromatids together are discussed. Dissolution of sister‐chromatid cohesion must be regulated precisely, and potential mechanisms to release cohesion are presented. (shrink)

There are many layers of regulation governing DNA replication to ensure that genetic information is accurately transmitted from mother cell to daughter cell. While much of the control occurs at the level of origin selection and firing, less is known about how replication fork progression is controlled throughout the genome. In Drosophila polytene cells, specific regions of the genome become repressed for DNA replication, resulting in underreplication and decreased copy number. Importantly, underreplicated domains share properties with common fragile sites. The (...) Suppressor of Underreplication protein SUUR is essential for this repression. Recent work established that SUUR functions by directly inhibiting replication fork progression, raising several interesting questions as to how replication fork progression and stability can be modulated within targeted regions of the genome. Here we discuss potential mechanisms by which replication fork inhibition can be achieved and the consequences this has on genome stability and copy number control. (shrink)

The chorion genes of Drosophila are amplified in response to developmental signals in the follicle cells of the ovary prior to their transcription. Their expression is regulated both temporally and spatially within this tissue. They thus serve as models both for the regulation of DNA replication and of developmental transcription. The regulatory elements for DNA amplification have been delineated. Their analysis reveals that amplification is mediated by several regulatory regions and initiates at defined origins within the chorion cluster. Proteins involved (...) in amplification are being identified both by mutations affecting amplification and by DNA binding studies. Regulatory elements for temporal as well as spatial control of chorion gene, expression have been characterized, and two candidate transcription factor genes have been cloned. (shrink)