Epithelial cell division in the Xenopus laevis embryo during gastrulation GUILLAUME HATTE 1,2 , MARC TRAMIER 1,2 , CLAUDE PRIGENT 1,2 and JEAN-PIERRE TASSAN* ,1,2 1 CNRS UMR 6290 and 2 Université de Rennes 1, Institut de Génétique et Développement de Rennes, Rennes, France ABSTRACT How vertebrate epithelial cells divide in vivo and how the cellular environment influ- ences cell division is currently poorly understood. A sine qua non condition to study cell division in situ is the ease of observation of cell division.This is fulfilled in the Xenopus embryo at the gastrula stage where polarized epithelial cells divide with a high frequency at the surface of the organism. Recently, using this model system, we have shown that epithelial cells divide by asymmetric fur- rowing and that the mode of cell division is regulated during development. Here, we further char- acterize epithelial cell division in situ. To this end, we used confocal microscopy to study epithelial cell division in the ectoderm of the Xenopus laevis gastrula. Cell division was followed either by indirect immunofluorescence in fixed embryos or by live imaging of embryos transiently expressing diverse fluorescent proteins. Here, we show that during cytokinesis, the plasma membranes of the two daughter cells are usually separated by a gap. For most divisions, daughter cells make contacts basally at a distance from the furrow tip which creates an inverted teardrop-like shaped volume tightly associated with the furrow. At the end of cytokinesis, the inverted teardrop is resorbed; thus it is a transient structure. Several proteins involved in cytokinesis are localized at the tip of the inverted teardrop suggesting that the formation of the gap could be an active process. We also show that intercalation of neighboring cells between daughter cells occasionally occurs during cytokinesis. Our results reveal an additional level of complexity in the relationship between dividing cells and also with their neighboring cells during cytokinesis in the Xenopus embryo epithelium. KEY WORDS: cytokinesis, asymmetric furrowing, contractile ring, anillin, actin, myosin Introduction Cytokinesis is the process by which dividing cells separate to produce two daughter cells. It is driven by a contractile ring com- posed of actin and myosin. It is commonly accepted that this ring is established perpendicularly to the mitotic spindle and is placed at equidistance of the mitotic chromosomes allowing their equal distribution to two daughter cells (Almonacid and Paoletti, 2010, Rappaport, 1996). The precise spatio-temporal regulation of the ring ensures the proper cell separation which otherwise could ultimately lead to abortive cytokinesis (Normand and King, 2010). Although a detailed mechanism of action is currently unknown, it is established that the actomyosin-based contractile ring produces the force necessary for ingression of the plasma membrane between the two daughter cells (Fededa and Gerlich, 2012). In addition to actin and myosin, multiple proteins are necessary to cytokinesis to Int. J. Dev. Biol. 58: 775-781 (2014) doi: 10.1387/ijdb.140277jt www.intjdevbiol.com *Address correspondence to: Jean-Pierre Tassan. IGDR, UMR 6290 CNRS Univ Rennes 1, 2 avenue du Professeur Léon Bernard, 35043 Rennes Cedex, France. E-mail: jean-pierre.tassan@univ-rennes1.fr Supplementary Material (3 movies and 3 igures) for this paper is available at: http://dx.doi.org/10.1387/ijdb.140277jt Accepted: 7 December 2014 ISSN: Online 1696-3547, Print 0214-6282 © 2014 UBC Press Printed in Spain Abbreviations used in this paper: MHC, myosin II heavy chain. proceed (Green et al., 2012). Anillin, a large multidomain protein is involved in the spatial positioning of the cleavage furrow during cytokinesis (Piekny and Maddox, 2010). Various anillin domains allow its interaction with cytokinetic proteins including actin, myosin and septin. In absence of anillin, the cytokinetic ring still forms, however it is not stably positioned. In isolated in vitro unpolarized cultured cells, the contraction of the contractile ring appears ap- proximately concentric. Vertebrate cell division is mostly studied in in vitro cultured cells. For example, isolated cells are particularly well suited for high-throughput screen (Kittler et al., 2004). Although, studies using the in vitro cultured cells have led to the discovery of basic mechanisms governing cytokinesis, it appears paradoxical that the majority of information on cell division of multicellular organisms