The EMBO Journal (2011) 30, 1690–1704 | & 2011 European Molecular Biology Organization | Some Rights Reserved 0261-4189/11 www.embojournal.org Regulation of interkinetic nuclear migration by cell cycle-coupled active and passive mechanisms in the developing brain THE EMBO JOURNAL EMBO open This is an open-access article distributed under the terms of the Creative Commons Attribution Noncommercial No Derivative Works 3.0 Unported License, which permits distribution and reproduction in any medium, provided the original author and source are credited. This license does not permit commercial exploitation or the creation of derivative works without speciﬁc permission. Yoichi Kosodo1,2,*, Taeko Suetsugu 1 , 2 3 Masumi Suda , Yuko Mimori-Kiyosue , 2 4 Kazunori Toida , Shoji A Baba , Akatsuki Kimura5 and Fumio Matsuzaki1,* 1Laboratory for Cell Asymmetry, RIKEN Center for Developmental Biology, Kobe, Japan, 2Department of Anatomy, Kawasaki Medical School, Kurashiki, Japan, 3Optical Image Analysis Unit, RIKEN Center for Developmental Biology, Kobe, Japan, 4Department of Biology, Ochanomizu University, Tokyo, Japan and 5Cell Architecture Laboratory, Center for Frontier Research, National Institute of Genetics, Shizuoka, Japan A hallmark of neurogenesis in the vertebrate brain is the apical–basal nuclear oscillation in polarized neural pro- genitor cells. Known as interkinetic nuclear migration (INM), these movements are synchronized with the cell cycle such that nuclei move basally during G1-phase and apically during G2-phase. However, it is unknown how the direction of movement and the cell cycle are tightly coupled. Here, we show that INM proceeds through the cell cycle-dependent linkage of cell-autonomous and non-autonomous mechan- isms. During S to G2 progression, the microtubule-associated protein Tpx2 redistributes from the nucleus to the apical process, and promotes nuclear migration during G2-phase by altering microtubule organization. Thus, Tpx2 links cell- cycle progression and autonomous apical nuclear migration. In contrast, in vivo observations of implanted microbeads, acute S-phase arrest of surrounding cells and computational modelling suggest that the basal migration of G1-phase nuclei depends on a displacement effect by G2-phase nuclei migrat- ing apically. Our model for INM explains how the dynamics of neural progenitors harmonize their extensive proliferation with the epithelial architecture in the developing brain. The EMBO Journal (2011) 30, 1690–1704. doi:10.1038/ emboj.2011.81; Published online 25 March 2011 Subject Categories: cell & tissue architecture; development Keywords: cell cycle; computational model; microtubule; neuroepithelial cell; Tpx2 *Corresponding authors. Y Kosodo, Department of Anatomy, Kawasaki Medical School, 577 Matsushima, Kurashiki 701-0192, Japan. Tel.: þ 81 86 462 1111; Fax: þ 81 86 462 1199; E-mail: kosodo@med.kawasaki-m.ac.jp or F Matsuzaki, Laboratory for Cell Asymmetry, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-Minamimachi, Chuou-ku, Kobe 650-0047, Japan. Tel.: þ 81 78 306 3217; Fax: þ 81 78 306 3215; E-mail: fumio@cdb.riken.jp Received: 19 May 2010; accepted: 23 February 2011; published online: 25 March 2011 1690 The EMBO Journal VOL 30 | NO 9 | 2011 Introduction During vertebrate development, brain tissues must maintain their structure even as they increase in complexity through the proliferation of neural progenitor cells and differentiation of their progeny. The neuroepithelium is polarized, with a basal side and an apical, ventricular surface that abuts the lumen of the neural tube early in development. The neuro- epithelial cells, which are highly elongated extending thin processes toward the basal and apical surfaces, initially grow their population through proliferation, and subsequently gives rise to neurogenic progenitor cells that both self- renew and generate neurons (Go¨ tz and Huttner, 2005). Proliferation of progenitor cells occurs in the ventricular zone (VZ), the apical-most region of neuroepithelium. Neurons and fate-committed progenitor cells migrate away from the VZ, transforming a single-layered pseudostratiﬁed tissue into a multi-layered tissue. Thus, the VZ is maintained as the major germinal layer throughout the enormous expansion of progenitor cells and the extensive production of neurons in brain development. Despite its importance, however, the mechanisms that maintain the VZ structure are not well understood. Neural progenitor cells in the VZ exhibit interkinetic nuclear migration (INM), in which their nuclei migrate between the apical surface and the basal part of the VZ in synchrony with the cell cycle (see Figure 1A). After mitosis at the apical surface (M-phase), the nuclei migrate basally during G1-phase and subsequently stay at the basal region of the VZ during S-phase. In G2-phase, the nuclei migrate apically, entering M-phase upon reaching the apical surface. This characteristic oscillation of the nuclei of neural progeni- tor cells was ﬁrst identiﬁed in the embryonic neuroepithelium more than 70 years ago (Sauer, 1935), and was experimen- tally veriﬁed thereafter (Sauer and Walker, 1959; Fujita, 1960). INM has been observed in other epithelial tissues, including chick basilar papilla (Raphael et al, 1994) and embryonic mouse liver buds (Bort et al, 2006), suggesting that this process is a hallmark not only of neuroepithelium, but of all pseudostratiﬁed epithelia. Notably, studies using mouse brain and zebraﬁsh retina have suggested that INM is critical for the self-renewal of neural progenitor cells (Xie et al, 2007; Del Bene et al, 2008; Zhang et al, 2009; Taverna and Huttner, 2010). The impor- tance of INM in the developing brain has prompted several attempts to identify underlying mechanisms. One drug treat- ment study using cell-cycle inhibitors suggested that the cell cycle controls nuclear migration, while nuclear migration does not control the cell cycle (Ueno et al, 2006). Previous studies using inhibitors of actin (Messier and Auclair, 1974; & 2011 European Molecular Biology Organization