Rotation Projects

Cell Size Regulation

The mechanism of cell size control is a fundamental mystery of cell biology.  We have shown that two activators of mitosis, Cdc25 and Cdc13, are expressed at a size-dependent concentration, which is unusual, because most proteins maintain a constant, size-independent concentration.  Thus, understanding the mechanism of their size-dependent expression is an important challenge, and a key piece of the size-control puzzle.  Cdc25 appears to be regulated transcriptionally, whereas Cdc13 appears to be regulated translationally.  Possible rotation projects include dissecting the mechanisms of size-dependent expression of either Cdc25 or Cdc13.

DNA Replication Kinetics

Heterochromatin regulates the timing of replication origin firing, however the mechanism by which it affects origin function is unknown.  We have developed a model of how origin timing is regulated in non-heterochromatic chromatin; now we want to test how heterochromatin affects this mechanism.  In particular, we want to manipulate the heterochromatic context at specific loci, measure the changes in origin timing and investigate the molecular mechanisms responsible for the change.  One possible rotation project would be to establish heterochromatin at a well-characterized origin, measure origin timing, which we presume will be delayed, and then test at which step origin firing is delayed.

High-Throughput, Genome-Wide, Single-Molecule Replication Mapping

Mapping of human DNA replication kinetics is complicated by the heterogeneous and inefficient nature of mammalian replication initiation.  Such heterogeneity can be deconvolved using single molecule analysis, however previous technology was unable to analyze replication kinetics at a genome-wide scale.  We have developed a genome-wide, single-molecule replication mapping technology called Optical Replication Mapping (ORM) that generates 100-fold coverage of the human genome, allowing to map initiation events that occur in as few as 1% of cells.  We have used ORM to map replication initiation in human cell lines and to test models of human replication timing.  Rotation projects include studying replication regulation in development and a chemical biological approach to increasing mapping resolution.