title: Cleavage, incomplete inversion, and cytoplasmic bridges in Gonium pectorale (Volvocales, Chlorophyta).
abstract: Multicellularity arose several times in evolution of eukaryotes. The volvocine algae have full range of colonial organization from unicellular to colonies, and thus these algae are well-known models for examining the evolution and mechanisms of multicellularity. Gonium pectorale is a multicellular species of Volvocales and is thought to be one of the first small colonial organisms among the volvocine algae. In these algae, a cytoplasmic bridge is one of the key traits that arose during the evolution of multicellularity. Here, we observed the inversion process and the cytoplasmic bridges in G. pectorale using time-lapse, fluorescence, and electron microscopy. The cytoplasmic bridges were located in the middle region of the cell in 2-, 4-, 8-, and 16-celled stages and in inversion stages. However, there were no cytoplasmic bridges in the mature adult stage. Cytoplasmic bridges and cortical microtubules in G. pectorale suggest that a mechanism of kinesin-microtubule machinery similar to that in other volvocine algae is responsible for inversion in this species.
authors: Takezono High School, 3-9-1 Takezono, Tsukuba, Ibaraki, Japan. ihitoshi16@gmail.com
authors: Hitoshi
authors: H
authors: Iida
authors: Shuhei
authors: S
authors: Ota
authors: Isao
authors: I
authors: Inouye
mesh_terms: D005075:Biological Evolution; D002455:Cell Division; D000460:Chlorophyta / Q000196:embryology* / Q000648:ultrastructure; D003593:Cytoplasm / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008856:Microscopy, Fluorescence; D013045:Species Specificity; D059008:Time-Lapse Imaging