Marshall's team is interested in what controls the intracellular geometry of organelle positioning. To address this topic, they focus on one organelle that is well-known for its specific positioning: the centriole.
The tethered pair of mother and daughter centrioles is the major component of the centrosome complex and also promotes the assembly of cilia. Thus cilia can act as a cell surface indicator of centriole positioning. The team used the unicellular alga Chlamydomonas reinhardtii, which normally has two cilia at its apex, to scan for mutants in which cilia were misplaced.
In certain misplaced cilia mutants, the fibers that normally tether mother and daughter centrioles were absent. The team found that whereas the mother centriole in these mutants continued to locate at the cell's apex, the daughter's position was random. Thus it seems that the mother's tight rein on the daughter is what keeps the young one in position.
Centrioles are normally closely linked to the nucleus, but in mutants that lacked the fibers connecting these two, it was again the nucleus that displayed a randomized positioning, not the centriole. The authors found evidence that the centrioles position two other organelles—the contractile vacuole and microtubule rootlets. From these combined data, they suggest that the mother centriole might in fact coordinate the positions of a whole subset of organelles.
The nucleus in mammalian cells is also found associated with centrosomes, indicating that the guiding influence of mother might well be conserved.