title: Whole-organ cell shape analysis reveals the developmental basis of ascidian notochord taper.
abstract: Here we use in toto imaging together with computational segmentation and analysis methods to quantify the shape of every cell at multiple stages in the development of a simple organ: the notochord of the ascidian Ciona savignyi. We find that cell shape in the intercalated notochord depends strongly on anterior-posterior (AP) position, with cells in the middle of the notochord consistently wider than cells at the anterior or posterior. This morphological feature of having a tapered notochord is present in many chordates. We find that ascidian notochord taper involves three main mechanisms: Planar Cell Polarity (PCP) pathway-independent sibling cell volume asymmetries that precede notochord cell intercalation; the developmental timing of intercalation, which proceeds from the anterior and posterior towards the middle; and the differential rates of notochord cell narrowing after intercalation. A quantitative model shows how the morphology of an entire developing organ can be controlled by this small set of cellular mechanisms.
authors.affiliation: Department of Molecular, Cell and Developmental Biology, and Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, CA, USA. veeman@ksu.edu
authors.forename: Michael T
authors.initials: MT
authors.lastname: Veeman
authors.forename: William C
authors.initials: WC
authors.lastname: Smith
mesh_terms: D000818:Animals; D016764:Cell Polarity; D048430:Cell Shape; D048429:Cell Size; D004625:Embryo, Nonmammalian / Q000166:cytology; D007814:Larva / Q000166:cytology; D008954:Models, Biological; D009672:Notochord / Q000033:anatomy & histology* / Q000166:cytology* / Q000196:embryology; D009928:Organ Specificity; D013623:Tail / Q000601:surgery; D013997:Time Factors; D014561:Urochordata / Q000166:cytology* / Q000196:embryology*