Field emission scanning electron microscopy and transmission electron microscopy studies of the chorion, plasma membrane and syncytial layers of the gastrula-stage embryo of the zebrafish Brachydanio rerio: a consideration of the structural and functional

Abstract

The structure of the chorion and plasma membranes of gastrula‐stage zebrafish Brachydanio rerio embryos were studied using field emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). These studies confirm the outer chorion membrane complex to be 1.5–2.5 μm in thickness and to consist of three layers, electron‐dense outer and innermost layers (0.2–0.3 and 1.0–1.6 μm in thickness respectively) separated by an electron‐lucent middle layer (0.3–0.6 μm in thickness). The middle and inner layers are pierced by pore canals. A granular to farinaceous nature of the thin outer surface of the outer layer of the chorion has been revealed for the first time. The study provides original TEM images of the plasma membrane structures of gastrula‐stage embryos, and FE‐SEM and TEM images showing the plasma membrane to have three morpohologically distinct regions, being prominently ridged and folded at the surface of the blastoderm, smooth over the syncytial layer at the vegetal pole and with an intermediate region between the animal and vegetal pole where folding develops in advance of the expanding blastodermal disc of cells. FE‐SEM and TEM studies reveal details of the syncytial layer (1–4 μm thick) beneath the smooth plasma membrane at the vegetal pole, containing cytoplasmic organelles and small yolk globules. The significance of the structural detail shown in these studies is considered in the light of the difficulties experienced in cryopreservation of the embryo resulting from the inability of achieving cryoprotectant penetration of the yolk mass.

Structural and ultrastructural characteristics of the yolk syncytial layer inProchilodus lineatus(Valenciennes, 1836) (Teleostei; Prochilodontidae)

“…Recent research on the epiboly and somite stages, suggests that the major problem for cryopreservation of zebrafish embryos is the difficulty in gaining sufficient cryoprotectant penetration, particularly in the yolk compartment (Rawson et al, 2000). Hagedorn et al (1996Hagedorn et al ( , 1997 showed cryoprotectant penetration in the blastoderm, but hardly any in the yolk, suggesting that the YSL is one of the main permeability barriers to water and cryoprotectants, hindering the chilling of fish embryos.…”

“…Hagedorn et al (1996Hagedorn et al ( , 1997 showed cryoprotectant penetration in the blastoderm, but hardly any in the yolk, suggesting that the YSL is one of the main permeability barriers to water and cryoprotectants, hindering the chilling of fish embryos. Therefore, there is a considerable interest in the study of this syncytial layer, which envelopes the yolk, in order to identify its structural, functional and physiological features (Rawson et al, 2000).…”

Cryopreservation of Embryos from Model Animals and Human

“…At the six-somite stage, the volume of the blastoderm increases to about 40%, leaving the yolk occupying 60% of the embryo (Hagedorn et al, 1997c). Between the chorion and the embryo is the perivitelline space filled with liquid with a chemical composition virtually identical to the surrounding medium (Rawson et al, 2000). The complexity of the teleost embryos is further increased by the unbalanced partial density of water in different compartments.…”

Assessment of Toxicity of Cdse/Cds/Zns/S,S-Dihydrolipoic Acid/Polyacrylic Acid Quantum Dots at Danio rerio Embryos and Larvae

“…Already after 1 or 2 days of incubation, some big deposited particles were notable (Figures 4(a) and 4(b)) in the tested QD suspensions with maximal concentration. Coagulation of the particles dropped their chance to get into chorion pores which are 500-700 nm wide according to the field emission scanning electron microscopy data [10].…”