The gastrulation stage ends when the blastoderm completely covers the yolk, characterizing the 100% epiboly
stage, which is marked by the presence of primary germ layers (endoderm, mesoderm and ectoderm) and the embryonic axis, giving rise to the subsequent stage characterized by organogenesis (Wolpert et al., 2000).
Quantitative RT-PCR analysis revealed that both Cs-pitx2 and Kb-pitx2 were maternally inherited and started the zygote expression after 30% epiboly
transition, and reached the first peak at 27-somite stage.
In order to evaluate the role of VPA in zebrafish notochord formation, the wild type zebrafish embryos were treated with various concentrations of VPA (20 to 40 -M from 50% epiboly
stage for 18 h.
Starting at 5.25 hpf (50% epiboly
), 20 viable wild-type embryos per replicate (with at least two replicates per treatment) were exposed under static conditions to vehicle (0.1% DMSO) or waterborne TDCPP (0.05-50 [micro]M), TCEP (0.05-50 [micro]M), TCPP (0.05-50 [micro]M), or V6 (0.05-50 [micro]M) until 96 hpf (24 hr posthatch).
At approximately 13 hours postfertilization, epiboly
began, and involution marked the start of gastrulation.
Gastrulation requires the migration of blastodermic cells over the yolk in the process of epiboly
Though the process of gastrulation was unknown, scanning electron micrographs suggested that part of the gastrulation process may have occurred by epiboly
, with micromeres moving to the vegetal pole and partially covering the macromeres (Fig.
The mode of gastrulation correlates with the amount of yolk: yolky embryos gastrulate by epiboly
; non-yolky embryos by invagination (Okada, 1970).
Over the next four days, the blastodermal cap flattened and increased in diameter as the edge began folding under (gastrulation) to form a germ ring that started moving downward over the yolk (epiboly
; Table 1).
Immediately preceding injection, dead embryos or embryos that had completed epiboly
were replaced, and the well water covering the embryos was replaced with a sterile saline solution.
proceeds, the cells that express gastropod Hb-like protein most intensely line the leading edge of the ectoderm as shown in I.
We scored fertilization at 2 HPF (elevated and translucent chorion; Yanagimachi el al., 1992); however, to ensure that spontaneous egg activation was not erroneously interpreted as fertilization, only embryos that progressed to the epiboly
stage of development (about 24 h after fertilization) were deemed fertilized.