Dicty News Electronic Edition Volume 19, number 13 December 7, 2002 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at DictyBase--http://dictybase.org. ============= Abstracts ============= ForC, a novel type of formin family protein lacking an FH1 domain, is involved in multicellular development in Dictyostelium discoideum. Chikako Kitayama and Taro Q.P. Uyeda Journal of Cell Science, in press. Summary Formins are highly conserved regulators of cytoskeletal organization and share three regions of homology: the FH1, FH2 and FH3 domains. Of the nine known formin genes or pseudogenes carried by Dictyostelium, forC is novel in that it lacks an FH1 domain. Mutant Dictyostelium lacking forC (forC) grew normally during the vegetative phase and, when starved, migrated normally and formed tight aggregates. Subsequently, however, forC cells made aberrant fruiting bodies with short stalks and sori that remained unlifted. forC aggregates were also unable to migrate as slugs, suggesting forC is involved in mediating cell movement during multicellular stages of Dictyostelium development. Consistent with this idea, expression of forC was increased significantly in aggregates of wild type cells. GFP-ForC expressed in forC cells was localized at the crowns, which are macropinocytotic structures rich in F-actin, suggesting that, like other formin isoforms, ForC functions in close relation with the actin cytoskeleton. Truncation analysis of GFP-ForC revealed that the FH3 domain is required for ForC localization; moreover, localization of a truncated GFP-ForC mutant at the site of contacts between cells on substrates and along the cortex of cells within a multicellular culminant suggests that ForC is involved in the local actin cytoskeletal reorganization mediating cell-cell adhesion. submitted by: c.kitayama@aist.go.jp ----------------------------------------------------------------------------- Title: Myosin II contributes to the posterior contraction and the anterior extension during the retraction phase in migrating Dictyostelium cells. Authors name: Kazuhiko S. K. Uchida, Toshiko Kitanishi-Yumura, and Shigehiko Yumura* Adress: Department of Biology, Faculty of Science, Yamaguchi University, Yamaguchi 753-8512, Japan *Author for correspondence Journal of Cell Science, in press Abstract: Cells must exert force against the substrate to migrate. We examined the vectors (both the direction and the magnitude) of the traction force generated by Dictyostelium cells, using an improved non-wrinkling silicone substrate. During migration, the cells showed two 'alternate' phases of locomotory behavior, an extension phase and a retraction phase. In accordance with these phases, two alternate patterns were identified in the traction force. During the extension phase, the cell exerted 'pulling force' toward the cell body in the anterior and the posterior regions and 'pushing force' in the side of the cell (pattern1). During the retraction phase, the cell exerted 'pushing force' in the anterior region, while the force disappeared in the side and the posterior regions of the cell (pattern2). Myosin II heavy chain null cells showed a single pattern in their traction force comparable to the 'pattern1', although they still had the alternate biphasic locomotory behavior similar to the wild type cells. Therefore, the generation of 'pushing force' in the anterior and the cancellation of the traction force in the side and the posterior during the retraction phase were deficient in myosin knock-out mutant cells, suggesting that these activities depend on myosin II via the posterior contraction. Considering all these results, we hypothesized the highly coordinated, biphasic mechanism of cell migration in Dictyostelium. submitted by: Uchida Kazuhiko [c2385@sty.cc.yamaguchi-u.ac.jp] ----------------------------------------------------------------------------- Involvement of A Novel Gene, zyg1, in Zygote Formation of Dictyostelium mucoroides Aiko Amagai Department of Developmental Biology and Neurosciences, Graduate School of Life Sciences, Tohoku University, Aoba, Sendai 980-8578, Japan Journal of Muscle Research and Cell Motility, Special Issue : Dictyostlium Ed. Dietmar J. Manstein, in press A gene, zyg1, was isolated by differential screening from Dictyostelium mucoroides 7 (Dm7) cells, as one preferentially expressed during their sexual development. The zyg1 gene encodes for a novel protein (ZYG1; deduced Mr 29.4 x 103 ) consisting of 268 amino acids. Although the ZYG1 protein has predicted PKC phosphorylation sites, it has neither transmenbrane domains nor specified signal sequences. The expression of zyg1 was initiated after 2 h of starvation and reached its maximum level at 8 h under submerged conditions. The expression pattern is quite similar to the temporal change of zygote formation during sexual development (macrocyst formation) with 1 h of precedence. The zyg1 mRNA in Dm7 cells developed on agar was retained until zygotes were formed. Zyg1- overexpressing cells derived from Dm7 cells eventually formed many loose mounds, in which giant cells were surrounded by normal-sized cells, in addition to mature macrocysts even under the conditions favouring for asexual sorocarp formation. The giant cells were found by DAPI-staining to be multinucleate, possibly because of the precocious overepxression of zyg1 mRNA. Western blottings using a specific antibody raised against the oligopeptide near the C-terminal region of ZYG1 also showed that ZYG1 was actually over-produced in the zyg1-overexpressing cells. From these results, it is evident that the zyg1 gene has an essential role in zygote formation by inducing sexual cell fusion. submitted by: Aiko Amagai [aiamagai@mail.cc.tohoku.ac.jp] ----------------------------------------------------------------------------- [End Dicty News, volume 19, number 13]