Organization and function of microfilaments during late epiboly in zebrafish embryos

Abstract

We report that, during epiboly in zebrafish, three F-actin-based structures appear only after the blastoderm migrates past the embryonic equator. They are composed of two ring-like F-actin structures that form at the deep cell and enveloping layer margins of the blastoderm and a punctate actin band that develops in the external yolk syncytial layer. Treatment with cytochalasin B or the calcium chelator dibromo-BAPTA results in the disruption of all three of these actin-based structures, leading to the slowing or immediate arrest of epiboly, respectively, followed by a failure of yolk cell occlusion and the eventual lysis of the embryo through the vegetal pole region. We suggest, therefore, that these structures function in the occlusion of the vegetal portion of the yolk cell during the latter stages of epiboly. Possible roles for these new structures, their modulation by Ca 2ϩ , as well as the functions of other previously described F-actin-based structures observed throughout epiboly, are discussed. Developmental Dynamics 231: 313-323, 2004.

ApoA-II Directs Morphogenetic Movements of Zebrafish Embryo by Preventing Chromosome Fusion during Nuclear Division in Yolk Syncytial Layer

“…The disorganization of eYSL may also perturb the F-actin band of the eYSL (32). A punctate band of filamentous actin (F-actin) has been described at the periphery of the eYSL and the EVL margin from 50% epiboly onwards (32,33).…”

“…A punctate band of filamentous actin (F-actin) has been described at the periphery of the eYSL and the EVL margin from 50% epiboly onwards (32,33). Therefore, we used anti-F-actin antibody to stain microfilament structures in the yolk.…”

Disruption of blastomeric F-actin: a potential early biomarker of developmental toxicity in zebrafish

“…Studies in Fundulus (Killifish) reveal an actin ring in the YSL adjacent to the blastoderm margin that is postulated to act as the "purse strings" during blastopore closure [7]. Three distinct actin structures become prevalent during late epiboly stages: two rings at the margin of the deep cells and the EVL; and a punctate band of actin accumulation in the external YSL adjacent to the EVL margin [8]. In zebrafish, a filamentous actin (F-actin) band is first evident at 50% epiboly in a similar location in the YSL [8].…”

“…Three distinct actin structures become prevalent during late epiboly stages: two rings at the margin of the deep cells and the EVL; and a punctate band of actin accumulation in the external YSL adjacent to the EVL margin [8]. In zebrafish, a filamentous actin (F-actin) band is first evident at 50% epiboly in a similar location in the YSL [8]. This actin band is associated with an active form of myosin, phosphorylated-myosin 2 [9], indicating the presence of an actin-myosin contractile activity in the YSL margin.…”

“…This actin band is associated with an active form of myosin, phosphorylated-myosin 2 [9], indicating the presence of an actin-myosin contractile activity in the YSL margin. This actin band is also involved in endocytosis [8], which removes the yolk membrane as the advancing blastoderm/EVL cells move vegetally over the yolk during epiboly. During early development, actin microfilaments throughout the embryo contribute to epiboly [8][9][10].…”