16.1  Monday, Jan. 4  Structural Components and Morphogenetic Mechanics of the Zebrafish Yolk Extension Developmental Module VIRTA, V. C. ; University of Washington virta@u.washington.edu

In order for a vertebrate embryo to attain a functional morphology, it must fundamentally change its shape from a sphere to an elongated rod. While cell movements on the dorsal side of the embryo have been extensively studied, morphogenetic cell behaviors shaping the ventrum have not been described at the same level of detail. The zebrafish yolk extension ontogenesis module serves as an excellent model for morphogenetic movements reshaping the ventrum because (1) the zebrafish embryo is optically transparent; (2) yolk extension ontogenesis occurs relatively quickly; and (3) the yolk cell isolates the tissues elongating the ventrum from the rest of the embryo. Furthermore, the zebrafish is an ideal taxon in which to perform studies of ventral cell movements, as these results can then be compared both to other teleosts, and other vertebrates.

From the core to the cortex of the embryo, three histological compartments comprise the yolk extension developmental module (1) the yolk cell; (2) the mesendodermal mantle; and (3) the embryonic integument. These structural compartments are hypothesized to interact with one another in a hierarchical manner, resulting in the morphogenesis of the elongated embryonic zebrafish ventrum. Time-lapse videomicroscopy and experimental manipulation show that the yolk mass is a viscoelastic, high-internal-phase emulsion, which resists compression. Moreover, ventral posterior mesoderm separates Kupffer’s Vesicle from the yolk cell. Finally, the embryonic integument is contractile and contributes to yolk extension formation. These experiments constitute an initial assessment of the morphogenetic mechanics underlying the zebrafish yolk extension ontogenesis module.