Fig. 1

tmi mutant embryos exhibit defects in cytokinesis. (A-H) Developmental time course of wild type (WT; A-D) and tmi mutant (E-H) embryos. In wild type, furrow formation (arrowheads in A,B) and cell division proceeds to generate a blastula. In tmi mutants, incipient furrows form (arrowhead in F) but do not fully contract during cell division, resulting in acellular embryos. (I-L) Immunolabeling of fixed embryos. (I) In wild type, labeling of microtubules (α-tubulin) and DNA (DAPI) show formation of furrows (arrowheads), including reorganization of the microtubular apparatus characteristic of maturing furrows (the FMA, arrowheads in I) as well as nuclear division. (J) In tmi mutants, furrows appear to initiate development as assessed by zones of microtubule exclusion (arrowheads), although the FMA does not fully form, exhibiting a reduction in microtubule enrichment. (K,L) Wild-type embryos (K) show accumulation of β-catenin in mature furrows (arrowhead), but tmi embryos (L) lack β-catenin accumulation (arrowhead). All phenotypes are 100% penetrant with 7-15 embryos per condition in I-L (see Materials and Methods). In spite of acellular phenotype, tmi mutant embryos appear fertilized, judged by the presence of sperm-dependent centrosomes (see Fig. 3 and Dekens et al., 2003; Lindeman and Pelegri, 2012; Yabe et al., 2007) and incipient furrows dividing cells into stereotypically placed, equally sized masses (F,J).