title: LET-99 determines spindle position and is asymmetrically enriched in response to PAR polarity cues in C. elegans embryos.
abstract: Asymmetric cell division depends on coordinating the position of the mitotic spindle with the axis of cellular polarity. We provide evidence that LET-99 is a link between polarity cues and the downstream machinery that determines spindle positioning in C. elegans embryos. In let-99 one-cell embryos, the nuclear-centrosome complex exhibits a hyperactive oscillation that is dynein dependent, instead of the normal anteriorly directed migration and rotation of the nuclear-centrosome complex. Furthermore, at anaphase in let-99 embryos the spindle poles do not show the characteristic asymmetric movements typical of wild type animals. LET-99 is a DEP domain protein that is asymmetrically enriched in a band that encircles P lineage cells. The LET-99 localization pattern is dependent on PAR polarity cues and correlates with nuclear rotation and anaphase spindle pole movements in wild-type embryos, as well as with changes in these movements in par mutant embryos. In particular, LET-99 is uniformly localized in one-cell par-3 embryos at the time of nuclear rotation. Rotation fails in spherical par-3 embryos in which the eggshell has been removed, but rotation occurs normally in spherical wild-type embryos. The latter results indicate that nuclear rotation in intact par-3 embryos is dictated by the geometry of the oblong egg and are consistent with the model that the LET-99 band is important for rotation in wild-type embryos. Together, the data indicate that LET-99 acts downstream of PAR-3 and PAR-2 to determine spindle positioning, potentially through the asymmetric regulation of forces on the spindle.
authors.affiliation: Section of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA.
authors.forename: Meng-Fu Bryan
authors.initials: MF
authors.lastname: Tsou
authors.forename: Adam
authors.initials: A
authors.lastname: Hayashi
authors.forename: Leah R
authors.initials: LR
authors.lastname: DeBella
authors.forename: Garth
authors.initials: G
authors.lastname: McGrath
authors.forename: Lesilee S
authors.initials: LS
authors.lastname: Rose
mesh_terms: D000705:Anaphase; D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology / Q000235:genetics; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D019070:Cell Lineage; D002467:Cell Nucleus / Q000378:metabolism; D016296:Mutagenesis; D017346:Protein Serine-Threonine Kinases; D008941:Spindle Apparatus / Q000502:physiology*
chemical_list: D029742:Caenorhabditis elegans Proteins; C467518:LET-99 protein, C elegans; C087977:par-2 protein, C elegans; C097238:PAR-3 protein, C elegans; D017346:Protein Serine-Threonine Kinases