Cytokinesis and Midzone Microtubule Organization inCaenorhabditis elegansRequire the Kinesin-like Protein ZEN-4

Abstract

Members of the MKLP1 subfamily of kinesin motor proteins localize to the equatorial region of the spindle midzone and are capable of bundling antiparallel microtubules in vitro. Despite these intriguing characteristics, it is unclear what role these kinesins play in dividing cells, particularly within the context of a developing embryo. Here, we report the identification of a null allele ofzen-4, an MKLP1 homologue in the nematodeCaenorhabditis elegans, and demonstrate that ZEN-4 is essential for cytokinesis. Embryos deprived of ZEN-4 form multinucleate single-celled embryos as they continue to cycle through mitosis but fail to complete cell division. Initiation of the cytokinetic furrow occurs at the normal time and place, but furrow propagation halts prematurely. Time-lapse recordings and microtubule staining reveal that the cytokinesis defect is preceded by the dissociation of the midzone microtubules. We show that ZEN-4 protein localizes to the spindle midzone during anaphase and persists at the midbody region throughout cytokinesis. We propose that ZEN-4 directly cross-links the midzone microtubules and suggest that these microtubules are required for the completion of cytokinesis.

Role of the Midbody Matrix in Cytokinesis: RNAi and Genetic Rescue Analysis of the Mammalian Motor Protein CHO1

“…The homologues of MKLP1/CHO1 studied thus far function in cytokinesis in diverse organisms (Adams et al, 1998;Powers et al, 1998;Raich et al, 1998;Chen et al, 2002;Matuliene and Kuriyama, 2002). However, there is some controversy regarding the stage of cytokinesis in which these proteins are involved.…”

“…However, there is some controversy regarding the stage of cytokinesis in which these proteins are involved. In C. elegans, the role of ZEN-4 appears to be restricted to completion of cytokinesis and maintenance of cell separation (Powers et al, 1998;Raich et al, 1998;Jantsch-Plunger et al, 2000;Severson et al, 2000). In contrast, Drosophila PAV-KLP has been suggested to be essential for assembly of the contractile ring and initiation of cytokinesis (Adams et al, 1998;Somma et al, 2002;Somers and Saint, 2003).…”

“…Two structures of the mitotic spindle, spindle asters (Rappaport, 1961) and the central spindle, have been implicated in induction of cleavage furrows. Although the central spindle appears to be essential in triggering cytokinesis in Drosophila (Adams et al, 1998;Giansanti et al, 1998;Somma et al, 2002;Somers and Saint, 2003) and mammalian cells (Cao and Wang, 1996), the same structure is largely dispensable for the furrow initiation in other systems, such as marine invertebrate eggs (Rappaport, 1961;Rappaport and Rappaport, 1983) and Caenorhabditis elegans (Raich et al, 1998;Jantsch-Plunger et al, 2000;Severson et al, 2000). Nonetheless, the presence of a central spindle has been shown to be essential for completion of cytokinesis in most systems (Wheatley and Wang, 1996;Raich et al, 1998;Jantsch-Plunger et al, 2000;Severson et al, 2000;Chen et al, 2002, Alsop andZhang, 2003).…”

“…The protein, named CHO1, turned out to be a plus-end-directed motor protein present in a wide range of organisms from humans (MKLP1: Nislow et al, 1992) and Drosophila (PAV-KLP: Adams et al, 1998) to C. elegans (ZEN-4: Raich et al, 1998). All those molecules are composed of well-conserved three subdomains: the mechanochemical motor domain at the N terminus, the central ␣-helical coiled-coil stalk, and the C-terminal globular tail.…”

“…However, CHO1 represents a unique isotype, in which an actin-binding sequence encoded by exon 18 is included in the middle of the tail domain . Members of the MKLP1 subfamily (Miki et al, 2001) have been shown to function in cytokinesis in different species (Adams et al, 1998;Powers et al, 1998;Raich et al, 1998;Chen et al, 2002;Matuliene and Kuriyama, 2002). In humans and C. elegans, the motor proteins interact with a GAP for Rho family GTPases, which facilitates microtubule bundling and formation of the spindle midzone and midbody (Mishima et al, 2002).…”