PgmNr W4040: t3421, a novel mutation required for bipolar spindle assembly in the one-cell stage C. elegans embryo.

Authors:
T. Mikeladze-Dvali 1 ; A. C. Erpf 1 ; N. Memar 1 ; R. Schnabel 2


Institutes
1) Biocenter, Ludwig-Maximilians-University, Munich, Germany; 2) Technical University Braunschweig, Braunschweig, Germany.


Keyword: Other ( centrosome )

Abstract:

Centrosomes, the primary microtubule organizing centers (MTOC) of animal cells, consist of a pair of centrioles surrounded by pericentriolar-material (PCM). As in many metazoans, in the nematode C. elegans, the sperm contributes the sole centriole pair to the zygote at fertilization, whereas the centrioles of the oocyte are eliminated during oogenesis. Upon fertilization, paternally derived centrioles disengage, duplicate and mature to centrosomes. During the process of maturation centrioles recruit maternal PCM proteins and assemble the centrosomes, which in turn are required for the formation of a bipolar spindle and faithful chromosome segregation. Our overall objective is to uncover molecular mechanisms that regulate maternal centrioles during oogenesis and to understand how paternally derived centrioles orchestrate bipolar spindle formation.

Among a set of temperature-sensitive embryonic lethal mutations, we identified the mutant allele t3421, which causes defective spindle assembly in early embryos. Live imaging of embryos at a restrictive temperature, revealed the formation of monopolar spindles during the first cell cycle, followed by an abnormal cytokinesis, as well as tri- or tetrapolar divisions in the second cell cycle. Our preliminary results suggest that one of the two paternally contributed centrioles is defective in the process of PCM assembly during the first mitosis, indicating a failure in centrosome maturation. Since only one of the centrioles fails to assemble a functional aster, we speculate that the affected centriole is the younger one of two paternally contributed centrioles.

Currently we are conducting experiments to further explore the molecular nature of the mutation and to gain a better understanding of the phenotype. So far the mutation has been mapped to a region on Chromosome I that among others includes a nonsense mutation in an unknown coiled-coiled domain protein.

We expect that the detailed analysis of t3421will provide key insights into the mechanisms of maturation of the paternally contributed centrioles.