Asymmetric cell division is of fundamental importance for generating cell diversity during development. Establishment of polarity and proper alignment of the mitotic spindle are both essential prerequisites for an asymmetric cell division. In the C. elegans one-cell embryo the first division is asymmetric and depends on the posterior positioning of the mitotic spindle along the axis of polarity. This asymmetry is the result of differential pulling forces acting on the spindle poles, with stronger net force acting on the posterior pole. The regulation of pulling forces is under the control of the PAR (partitioning defective)-proteins. Downstream of the PAR proteins heterotrimeric G protein signaling and receptor independent activators of G protein signaling GPR-1 and GPR-2 are involved in regulating spindle positioning. We are interested in understanding how spindle positioning is controlled. To identify new genes required for this process we have performed a screen for genes that can enhance the lethality of a temperature-sensitive allele of
gpr-1. In this screen we have identified T24H10.6 as a putative candidate genetically interacting with
gpr-1. T24H10.6 is the C. elegans homologue of Drosophila Roadblock (robl), a member of dynein light chain family of proteins which have been shown to play a role in microtubule based process of axonal transport, flagellar motility and mitosis. Depletion of T24H10.6 in a wild-type background results in 50% embryonic lethality. These embryos display defects in pronuclei centration, rotation and spindle rocking, but no strong defects in pronuclear migration. Depletion of T24H10.6 in
gpr-1 mutant animals leads to more severe defects in the embryo, similar to the defects observed upon depletion of DHC-1. Pronuclear migration is delayed, the mitotic spindle is set up posteriorly and perpendicular to the longitudinal axis of the embryo. We are interested in understanding how T24H10.6 signaling is linked to the heterotrimeric G protein signaling. Progress will be presented at the meeting.