Studies by my laboratory focus on
spindle and chromosome dynamics, and
the mechanisms that ensure proper chromosome
transmission and inheritance. We are
especially interested in molecular
motor proteins and the roles of motors
in force production and dynamics of
chromosomes and spindles.
More than 10 years ago, my laboratory
identified a kinesin-related microtubule
motor protein, Ncd, that is required
for normal chromosome distribution
in Drosophila. We showed using in vitro
motility assays that Ncd moves on microtubules
towards the stable minus ends, rather
than towards the fast depolymerizing/polymerizing
plus ends, like conventional kinesin
and other kinesin motors. We recently
determined the molecular basis of the
unexpected reversed directionality
of Ncd movement on microtubules and
identified the region of the motor
required for minus-end movement. We
also recently identified a large conformational
change of the coiled-coil stalk of
Ncd that we believe is involved in
force production and directed movement
of the motor.
Our current efforts are to determine
the mechanism of Ncd function in chromosome
segregation. We previously localized
the Ncd motor to meiotic and mitotic
spindles, and showed that ncd mutants
exhibit highly abnormal meiotic spindles
and frequent loss of centrosomes and
chromosomes from mitotic spindles.
These findings imply that Ncd is needed
for assembly of normal meiotic spindles
and attachment of centrosomes and chromosomes
to mitotic spindles. Using a fusion
of Ncd to GFP, we have followed spindle
dynamics in live oocytes and embryos
- we visualized the meiotic divisions
in oocytes for the first time and followed
mitotic divisions in wild-type and
mutant embryos. Microtubule motors
similar to Ncd probably exist in most
or all eukaryotes, where they perform
roles in meiosis and mitosis that include
spindle pole formation, attachment
of centrosomes to spindle poles, and
mediation of poleward chromosome movement
by sliding microtubules and kinetochores
poleward.
Students can participate in these
studies by carrying out molecular genetics
studies to determine the mechanism
of Ncd function in the cell by constructing
and analysing specific mutants, or
molecular and biochemical studies to
determine how the motor functions in
vitro.
