08-P001 Interkinetic nuclear migration in the zebrafish retina: Actomyosin contraction is the prime mover

MECHANISMS OF DEVELOPMENT

1 2 6 ( 2 0 0 9 ) S 1 4 4 –S 1 5 0

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Asymmetry in cells 08-P001

ise to the distal edge of the cell, with Strabismus and Prickle at

Interkinetic nuclear migration in the zebrafish retina: Actomyo-

the proximal edge of adjacent cells. Flamingo forms homodimers

sin contraction is the prime mover

across the intermembrane space.

Caren Norden1, Stephen Young1, Brian Link2, William Harris1

The mechanism of localisation of the cassette involves vesic-

1

ular transport of the transmembrane proteins (Flamingo, Frizzled

2

and possibly Strabismus). How is this regulated? Literature on

Cambridge University, Cambridge, United Kingdom Medical College of Wisconsin, Milwaukee, United States As the neurogenerative epithelium of the vertebrate central

nervous system expands during embryonic development, nuclei of neural progenitors undergo a process called interkinetic nuclear migration (IKNM). The nuclear movements of IKNM are generally believed to involve gradual migrations from apical to basal and back during the G1 and G2 phases of the cell cycle, respectively. Yet the kinetics of IKNM and the mechanisms that drive it have never been systematically studied. We use a high-resolution time-lapse confocal microscopy approach to record nuclear movements in zebrafish retinal neuroepithelial cells and show that, rather than being gradual and directed, nuclear movements are mainly stochastic except for brief apical nuclear translocations preceding mitosis. We also demonstrate that IKNM is driven largely by actomyosin contractions rather than transport along microtubules, as

localisation of transmembrane proteins implicates ubiquitination as a trigger for endocytosis and vesicular trafficking. I performed an invivo screen using RNAi lines to knock-down levels of components of the ubiquitination pathway and assayed their effects on polarity in the Drosophila wing. If ubiquitination triggers endocytosis, reducing ubiquitination would be expected to increase levels of core polarity proteins at the AJ. I found a group of genes whose knock down causes a marked accumulation of polarity proteins at the AJ. Surprisingly these corresponded to the Nedd8 conjugating pathway. Nedd8 is a ubiquitin-like molecule which is best characterised in regulation of Cullin based RING E3 ubiquitin ligases. Neddylation of Cullins activates these E3 ligases, increasing ubiquitination of targets. RNAi to Cullin-3 also caused accumulation of polarity proteins at the AJ. I am currently characterising the role of the Nedd8 pathway and Cullin 3 in regulating polarity protein levels and localisation.

these movements still occur when the microtubule cytoskeleton is destabilized or demolished yet they are severely inhibited when

doi:10.1016/j.mod.2009.06.309

Myosin II activity is blocked. Based on our findings we propose that nuclear movements during IKNM are reminiscent of movements of people at a crowded party held in a room with a bar at one end. People get thirsty and go to the bar to get a drink. Then they move or are pushed away to make room for others at the bar. Between drinks the partygoers jostle around the room, but when one of them gets thirsty again, he returns to the bar in a fast and directed manner.

08-P003 Regulation of asymmetric cell division by Wnt signaling through asymmetric spindle microtubules in Caenorhabditis elegans Kenji Sugioka, Hitoshi Sawa Riken Center for Developmental Biology, Kobe, Japan Department of Biology, Graduate School of Science, Kobe University,

doi:10.1016/j.mod.2009.06.308

08-P002 Characterisation of the role of ubiquitin-like molecules in regulating sub-cellular trafficking of core planar polarity proteins in the Drosophila wing Elizabeth Searle, Helen Strutt, David Strutt University of Sheffield, Sheffield, United Kingdom

Kobe, Japan Asymmetric cell division is a fundamental for the generation of cellular diversity. In Caenorhabditis elegans, asymmetry of a number of cell divisions are regulated by a Wnt pathway, called Wnt/b-catenin asymmetry pathway. In this pathway, we showed that Wnts instructively controls asymmetric cortical localization of proteins, such as WRM-1/b-catenin and APR-1/APC. Then, during telophase of divisions, asymmetric nuclear localization of WRM-1/b-catenin and POP-1/TCF are established through the

Planar polarity describes asymmetry within the plane of an

function of the cortical proteins. However, mechanisms for asym-

epithelium. It has been studied in detail in the Drosophila wing,

metric localizations have not been elucidated. We found that a

where the unidirectional orientation of trichomes depends on

Wnt regulates formation of asymmetric spindle structure in an

correct localisation of a core cassette of planar polarity proteins

embryonic cell. Specifically at telophase, the posterior centro-

at the apical junctions (AJ). Frizzled, Dishevelled and Diego local-

some has fewer astral microtubules than the anterior one. This