View Program - 63rd Annual Drosophila Research Conference

Mitosis and meiosis are the most exciting and elaborate processes that occur during the life of
dividing cells however, defects in these processes can lead to aneuploidy and lethal phenotypes.
Errors in chromosomal segregation in oocytes lead to infertility and birth defects. We use
Drosophila to understand the mechanisms of homologous chromosome bi-orientation that occurs
during meiosis I, and the features of the oocyte-spindle that make it susceptible to segregation
errors. The chromosome passenger complex (CPC) is a highly conserved master regulator that is
required for oocyte spindle assembly, kinetochore assembly and homologous chromosome
biorientation. It is a complex consisting of the proteins INCENP, Aurora B kinase, Survivin and
Borealin. The CPC is recruited by the chromosomes and then moves to the microtubules. The
mechanisms of this movement and the CPC signaling pathway that recruits and promotes the
activity of kinetochore and spindle proteins remains largely unknown. Our previous research has
led to a model that Borealin promotes spindle assembly in Drosophila oocytes by interacting
with nucleosomes or the chromatin protein HP1. It was hypothesized that a Borealin-HP1
interaction is necessary for CPC binding to the chromosomes and movement to the microtubules.
We are testing this model by mutating two domains within Borealin that may support this
function: (1) a domain for binding HP1 and (2) a domain for binding microtubules. For these
experiments, we have generated two Borealin shRNA lines and found that depletion of Borealin
by RNAi showed phenotypes similar to aurB and or Incenp RNAi; complete loss of kinetochore
and spindle assembly. Interestingly, many of the oocytes exhibited fragmented karyosomes,
suggesting a role for the CPC in oocyte chromatin organization. We are currently generating
RNAi resistant transgenes to that express borr mutants that are defective interacting with either
nucleosomes / HP1 or microtubules. Parallel to these studies, we are examining the phenotype of
Incenp mutants predicted to be defective in microtubule interactions and trying to directly detect
interactions between HP1 and either INCENP or Borealin in oocytes.

A Borealin-HP1 Interaction Regulates Chromosome Passenger Complex Binding to Chromosomes and Movement to Microtubules