title: Dynamic microtubules at the vegetal cortex predict the embryonic axis in zebrafish.
abstract: In zebrafish, as in many animals, maternal dorsal determinants are vegetally localized in the egg and are transported after fertilization in a microtubule-dependent manner. However, the organization of early microtubules, their dynamics and their contribution to axis formation are not fully understood. Using live imaging, we identified two populations of microtubules, perpendicular bundles and parallel arrays, which are directionally oriented and detected exclusively at the vegetal cortex before the first cell division. Perpendicular bundles emanate from the vegetal cortex, extend towards the blastoderm, and orient along the animal-vegetal axis. Parallel arrays become asymmetric on the vegetal cortex, and orient towards dorsal. We show that the orientation of microtubules at 20 minutes post-fertilization can predict where the embryonic dorsal structures in zebrafish will form. Furthermore, we find that parallel microtubule arrays colocalize with wnt8a RNA, the candidate maternal dorsal factor. Vegetal cytoplasmic granules are displaced with parallel arrays by ~20°, providing in vivo evidence of a cortical rotation-like process in zebrafish. Cortical displacement requires parallel microtubule arrays, and probably contributes to asymmetric transport of maternal determinants. Formation of parallel arrays depends on Ca(2+) signaling. Thus, microtubule polarity and organization predicts the zebrafish embryonic axis. In addition, our results suggest that cortical rotation-like processes might be more common in early development than previously thought.
authors.affiliation: Temasek Life Sciences Laboratory, 1 Research Link, 117604 Singapore.
authors.forename: Long Duc
authors.initials: LD
authors.lastname: Tran
authors.forename: Hiromu
authors.initials: H
authors.lastname: Hino
authors.forename: Helen
authors.initials: H
authors.lastname: Quach
authors.forename: Shimin
authors.initials: S
authors.lastname: Lim
authors.forename: Asako
authors.initials: A
authors.lastname: Shindo
authors.forename: Yuko
authors.initials: Y
authors.lastname: Mimori-Kiyosue
authors.forename: Marina
authors.initials: M
authors.lastname: Mione
authors.forename: Naoto
authors.initials: N
authors.lastname: Ueno
authors.forename: Christoph
authors.initials: C
authors.lastname: Winkler
authors.forename: Masahiko
authors.initials: M
authors.lastname: Hibi
authors.forename: Karuna
authors.initials: K
authors.lastname: Sampath
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001756:Blastoderm / Q000196:embryology / Q000378:metabolism; D019521:Body Patterning / Q000235:genetics; D020013:Calcium Signaling / Q000502:physiology; D002540:Cerebral Cortex / Q000196:embryology* / Q000648:ultrastructure; D004625:Embryo, Nonmammalian; D005260:Female; D005306:Fertilization / Q000502:physiology; D005544:Forecasting; D049452:Green Fluorescent Proteins / Q000235:genetics; D008297:Male; D008870:Microtubules / Q000502:physiology*; D013084:Sperm-Ovum Interactions / Q000502:physiology; D014981:Xenopus; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics
chemical_list: D049452:Green Fluorescent Proteins