[
C. elegans: Development and Gene Expression, EMBL, Heidelberg, Germany,
2010]
To further understand the mechanisms controlling spindle positioning during asymmetric cell division, we are comparing the one-cell stage embryo of different Caenorhabditis species. Despite constancy in the final phenotype (an asymmetric division with a small posterior cell), we found that nuclei and mitotic spindle movements prior to division differ between species. We are currently concentrating on C. elegans and C. briggsae comparisons in the hope to identify different (and hopefully new) equivalent solutions for the control of spindle positioning. In C. elegans, the spindle sets up in the center of the cell and is further displaced towards the posterior pole, due to an unbalanced of pulling forces acting on the asters. As the posterior pole is strongly pulled, it undergoes large tran sverse oscillations. Importantly, the mitotic spindle sets up in the anterior part of C. briggsae embryos and asters undergo limited transverse oscillations during anaphase, suggesting that a larger elongation of the spindle is taking place despite weaker pulling forces compared to C. elegans. We are trying to solve this paradox by a combination of actual measurement of forces using laser microdissection of microtubules, mathematical modeling of spindle movements and analysis of the C. briggsae orthologs of known C. elegans molecular player. We performed systematic RNAi inactivation of the genes and established several lines of GFP fused proteins to follow their dynamic localization in the early embryo of C. briggsae.