Microtubule motors are multi-molecular machines that ferry cargoes within a cell. We have been studying dynein, the minus-end directed microtubule motor, and MEL-28, a conserved protein important for nuclear envelope integrity and post-mitotic rebuilding of the nuclear pore.
dhc-1(
or283ts);
mel-28(
t1684) double mutants have a severely reduced brood size compared to each single mutant. This suggests that MEL-28 and dynein act in parallel to support a process necessary for fertility. Reciprocal crosses between wild-type animals and
dhc-1;
mel-28 double mutants revealed that the brood size impairment is caused by oogenic germ line defects and not sperm defects. Indeed,
dhc-1;
mel-28 double mutant adults have a disorganized proximal gonad and oocyte maturity defects. To find cellular components that regulate MEL-28/dynein supported processes, we did a candidate RNAi screen searching for genes that rescue the brood size of
dhc-1;
mel-28 double mutants. We found that disruption of
klc-2, which encodes the light chain of the plus-end-directed microtubule motor kinesin-1, increases the brood size of
dhc-1;
mel-28 double mutants. This suggested that simultaneous disruption of MEL-28 and dynein causes excessive plus-end-directed movement of a cargo that is rescued by impairing plus-end-directed motion via
klc-2 RNAi. Kinesin and dynein work together through physical interactions with KASH-domain protein UNC-83 to regulate nuclear positioning. We tested the idea that aberrant UNC-83-dependent nuclei positioning in
dhc-1;
mel-28 double mutants contributes to the low brood size defect. Connectivity between dynein and UNC-83 is mediated via dynein adaptors NUD-2 and BICD-1. In
bicd-1;
nud-2 double mutants, the connection between UNC-83 and dynein is defective. If
dhc-1;
mel-28 animals are infertile because UNC-83-dependent minus-end directed nuclear movement is impaired, then we would expect that
mel-28;
bicd-1;
nud-2 triple mutants to have a low brood size. Indeed, the triple mutant shows a lower brood size than
bicd-1;
nud-2 double mutants and
mel-28 single mutants, supporting the idea that defects to
mel-28 sensitize the oogenic gonad to defects with UNC-83-dependent minus-end-directed movement of the nuclei. These observations suggest that MEL-28 and dynein-mediated connections to UNC-83 work collaboratively to position nuclei for proper oogenic development.