Wilson cell origin for kupffer's vesicle in the zebrafish

Background: Bilaterally symmetric animals have evolved highly reproducible asymmetries between left and right. In teleosts, Kupffer's vesicle, the structure necessary for the determination of left-right asymmetry, is derived from a group of cells in the gastrula termed the dorsal forerunners. Results: Wilson cells are a ring of marginal enveloping layer cells that are cytoplasmically connected to the yolk cell and thus the last blastomeres to inherit yolk cell cytoplasm. Afterward, they collapse into the yolk to form the yolk syncytial layer. Without exception, forerunner cells are the progeny of dorsal Wilson cells. At the beginning of gastrulation, these Wilson cell progeny ingress beneath the enveloping layer, transform into Kupffer's vesicle, and eventually become tail notochord and muscle. Before ingressing, the forerunner precursor cells express endodermal promoting genes and require high-levels of Nodal signaling. Conclusions: Despite a derived function of the enveloping layer as an epithelium covering the entire embryo, its dorsal margin retains many behaviors of what might be expected of the dorsal superficial layers of the ancestral fish embryo, including an early program of endodermal development, cell ingression, and an eventual contribution of cells to caudal notochord and muscle, as well as the control of laterality. Developmental Dynamics 247:1057-1069, 2018. (c) 2018 Wiley Periodicals, Inc.