Identification of genes required for nuclear envelope formation using living Caenorhabditis elegans embryos

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In the laboratory of Iain W. Mattaj we use the nematode Caenorhabditis elegansto analyse nuclear envelope formation in vivo. The current worm workers are Vincent Galy and Peter Askjaer. Below you see a summary of our main work and links to movies and some of the data we have obtained.


When a eukaryotic cell divides the duplicated chromatin has to be precisely segregated and enclosed by a new nuclear envelope (NE). Failure in these key processes results in dramatic alterations of gene expression patterns and genome instability. To identify and characterize components that regulate mitosis, intially focussing mainly on NE formation, we study early embryogenesis in C. elegans. Due to its well-characterized and rapid embryogenesis C. elegans provides a powerful model system for the analysis of mitotic events. In addition, depletion of gene products by RNA interference (RNAi) is extremely efficient in the nematode and allows evaluation of gene function also on a whole-organism scale.
    We have analyzed the small GTPase Ran and its associated co-factors for the first time using live cell imaging. Ran has previously been shown to regulate mitotic spindle formation and NE assembly in cell free extracts. We could confirm those observations in vivo and extend them further to include a requirement for Ran-mediated GTP hydrolysis during spindle formation. Importantly, we have found that depletion of importins alpha and beta cause an identical phenotype suggesting that these transport factors act downstream of Ran during mitosis (Mol. Biol. Cell 13, 4355-4370).
    A systematic depletion of nucleoporins, which are the components of the nuclear pore complex, has surprisingly shown that several of these proteins are essential for reforming the nucleus after mitosis. This means that certain nucleoporins have important functions prior to their established roles in nucleocytoplasmic transport. We have annotated 20 nucleoporin genes, npp-1 through npp-20, of which 12 were found to be absolutely required for viability. Combinatorial RNAi has revealed that a further five nucleoporins play important roles in embryogenesis. We are currently analyzing the defects caused upon depletion of specific nucleoporins in greater detail. These defects range from alteration in nuclear pore complex permeability to inhibition of NE formation (Mol. Biol. Cell in press).


Follow these link to:
Transgenic strains
Movies from RNAi experiments
Primers used to generate RNAi constructs
If you want to learn more about this small animal take a look at Caenorhabditis elegans WWW Server or WormBase, which both have plenty of useful information and links.
The background shows still images from a time-lapse video of an embryo expressing GFP-alpha-tubulin(Oegema et al., J. Cell Biol. 153, 1209). Initially, the two pronuclei are positioned at opposite ends of the embryo but later they meet in the interior of the embryo. The pronucelar envelopes break down and a mitotic spindle is formed. The spindle segregates the two sets of chromosomes toward the poles and the embryo divides. In each of the daughter cells a new nucleus is formed, surronded by a nuclear envelope. Recorded in collaboration with Eva Hannak.

Author: Peter Askjaer; Last change: 28 08 2003; Mattaj group