Developmental Toxicity Assessment in Zebrafish - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 15

throughout development—blastula through advanced organogenesis—compared to
rodent embryo culture that is limited to early organogenesis, and (4) the zebrafish
genome iswell characterized and dysmorphology phenotypes linked to genomic targets
can potentially enable rapid evaluation of mechanisms of action for compound-induced
teratogenicity. Here, we describe methods for assessing developmental toxicity in
zebrafish and recent results.

2.2 METHODS

2.2.1 Zebrafish Developmental Toxicity Screen

Compounds that induce defects in embryo morphology or organ function before
causing death are defined as teratogens and the zebrafish toxicity assay is designed to
assess lethality and toxicity curves. Multiple concentrations of each compound are
tested for the duration of embryogenesis and 10-30 animals are typically used for
each concentration.
Compared with other animal models, rapid development is a significant advantage
for assessing compound developmental toxicity in zebrafish (Table 2.1); organogenesis
is essentially complete within the first 5 days of development (Westerfield, 1993). Due
to transparency, organs can be assessed in vivo directly by microscopy without use of
complicated dissecting procedures.

2.2.2 Embryo Selection and Drug Treatment

The stages for initiating and terminating compound treatment are critical parameters
for assessing developmental toxicity. Since zebrafish organ development is completed
by 5dpf, this stage is usually used for terminating compound treatment. To evaluate
compound effects throughout gastrulation, it is important to initiate compound

Table 2.1 Comparison of Embryo Development in Zebrafish, Mouse, and Humans

Stage of embryonic development Zebrafish Mouse Humans

Cleavage period 0-2hpf Days 1-2 Days 1-5

1 1 / 4 hpf 8-cell stage Day 4

5 1 / 4 -10hpf Gastrulation Days 6-8 Weeks 2-4

Initial neurulation 9hpf Day 8 Day 22

Formation of five brain ventricles 30hpf Day 10 Weeks 5-9

Heart formation 22hpf Day 8 Day 16

Heart beat 30hpf Day 8 Day 22

Organogenesis 24-48hpf Days 8-14 Weeks 4-8

Initial craniofacial development 24hpf Day 8 Day 22