Intracellular organelles mediate cytoplasmic pulling force for centrosome centration in the Caenorhabditis elegans early embryo

Abstract

The centrosome is generally maintained at the center of the cell. In animal cells, centrosome centration is powered by the pulling force of microtubules, which is dependent on cytoplasmic dynein. However, it is unclear how dynein brings the centrosome to the cell center, i.e., which structure inside the cell functions as a substrate to anchor dynein. Here, we provide evidence that a population of dynein, which is located on intracellular organelles and is responsible for organelle transport toward the centrosome, generates the force required for centrosome centration in Caenorhabditis elegans embryos. By using the database of full-genome RNAi in C. elegans, we identified dyrb-1, a dynein light chain subunit, as a potential subunit involved in dynein anchoring for centrosome centration. DYRB-1 is required for organelle movement toward the minus end of the microtubules. The temporal correlation between centrosome centration and the net movement of organelle transport was found to be significant. Centrosome centration was impaired when Rab7 and RILP, which mediate the association between organelles and dynein in mammalian cells, were knocked down. These results indicate that minus end-directed transport of intracellular organelles along the microtubules is required for centrosome centration in C. elegans embryos. On the basis of this finding, we propose a model in which the reaction forces of organelle transport generated along microtubules act as a driving force that pulls the centrosomes toward the cell center. This is the first model, to our knowledge, providing a mechanical basis for cytoplasmic pulling force for centrosome centration.endosome | lysosome | pronuclear migration | the centrosome-organelle mutual pulling model | yolk granule

A novel mechanism of microtubule length-dependent force to pull centrosomes toward the cell center

“…23 However, based on our theoretical estimation of the force balance, a very small number of minusend-directed organelle movements should be sufficient for centering. 24 Thus, if the number of minus-end-directed movements slightly exceeds the number of plus-end-directed movements, sufficient force would be generated to move the centrosome. Consistent with this idea, we observed less plus-end-directed movements of the organelles than minus-enddirected movements in wild-type cells of C. elegans embryos.…”

“…9,[21][22][23] We refer to the structure as the "centrosome centration anchor." 24 The centrosome centration anchor may be located at the cell cortex [ fig. 1a(b)] or throughout the cytoplasm [ fig.…”

“…3). 24 We first screened candidate genes involved selectively in the centrosome centration anchor in C. elegans embryos ( fig. 3a and b) and found DYRB-1, a light chain involves the length-dependent depolymerization of microtubules.…”

Polarity Control of Spindle Positioning in the C. elegans Embryo

“…Because of the resistance of the viscous cytoplasm, this generates a dragging force at centrosomes. This mechanism may contribute to centration because microtubules extending toward the anterior are longer, and the majority of organelles are anterior of the maternal and paternal pronucleus at the time of meeting (Kimura and Kimura 2011). Another mechanism proposed to contribute to the centration of the pronuclei-centrosomal complex is the sliding of microtubules along the cortex, when microtubules are not attached end-on but laterally by a cortical LIN-5/dynein complex (Gusnowski and Srayko 2011).…”

“…Dynein acting independently of the LIN-5 pulling force complex has been proposed to contribute to centration movements (Kimura and Kimura 2011). The dynein light chain protein, dynein roadblock (DYRB-1), anchors organelles for transport along microtubules.…”