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6.1 Early Zebrafish Development
and Embryonic Patterning
M. Hild et al.
Development of the zebrafish starts with a single cell, the fertilized egg,
also called the zygote. After fertilization, the embryo undergoes a rapid
succession of cell cleavages, cell specifications, and morphogenetic
events which are strictly coordinated temporally and spatially, and
which within two days lead to a larva that very much resembles the
adult fish. Important morphogenetic processes occur during gastrulation
when the embryo becomes multilayered (Warga and Kimmel 1990).
Three germ layers - ectoderm, endoderm, and mesoderm - become
evident, and endoderm and mesoderm are moved into the interior of the
embryo. During further development, the ectoderm will give rise to skin
and fins (epidermal fates) and to the central nervous system; the endoderm to the digestive system (stomach, gut, liver, pancreas etc.); and the
mesoderm to muscle, the skeletal system, the blood, the vascular system, and the remaining inner organs such as heart and kidney (pronephros).
Before gastrulation, during blastula stages, the embryo is rather
simply structured and appears radially symmetrical, with an animalvegetal polarity, reflecting the presumptive anteroposterior axis, but
with no morphologically apparent dorsoventral polarity. Despite this
morphological symmetry, however, several genes display a differential
dorsoventral expression pattern, indicating that positional values along
the presumptive dorsoventral axis are already defined at pregastrula
stages. In addition, cell lineage-tracing experiments indicate that fates
of cells depend on their position within the early blastula embryo
(Kimmel et al. 1990). Along the animal-vegetal axis, the fate map of the
blastula embryo is rather simple; cells in animal regions of the blastula
embryo give rise to ectodermal fates, while cells from the marginal
regions form endodermal and mesodermal derivatives. A more complex
pattern is observed for the fate map along the presumptive dorsoventral
axis; dorsal animal cells will form neuroectoderm, while ventral animal
cells will form epidermal structures like skin and fins. Of the presumptive mesoderm in the marginal zone, dorsal-most cells will form the
hatching glands and the notochord, dorsolateral cells the heart and
somites, ventrolateral cells the pronephros, and ventral-most cells will
form blood. In this chapter, we will study how positional values within
6.1 Early Zebrafish Development
and Embryonic Patterning
M. Hild et al.
Development of the zebrafish starts with a single cell, the fertilized egg,
also called the zygote. After fertilization, the embryo undergoes a rapid
succession of cell cleavages, cell specifications, and morphogenetic
events which are strictly coordinated temporally and spatially, and
which within two days lead to a larva that very much resembles the
adult fish. Important morphogenetic processes occur during gastrulation
when the embryo becomes multilayered (Warga and Kimmel 1990).
Three germ layers - ectoderm, endoderm, and mesoderm - become
evident, and endoderm and mesoderm are moved into the interior of the
embryo. During further development, the ectoderm will give rise to skin
and fins (epidermal fates) and to the central nervous system; the endoderm to the digestive system (stomach, gut, liver, pancreas etc.); and the
mesoderm to muscle, the skeletal system, the blood, the vascular system, and the remaining inner organs such as heart and kidney (pronephros).
Before gastrulation, during blastula stages, the embryo is rather
simply structured and appears radially symmetrical, with an animalvegetal polarity, reflecting the presumptive anteroposterior axis, but
with no morphologically apparent dorsoventral polarity. Despite this
morphological symmetry, however, several genes display a differential
dorsoventral expression pattern, indicating that positional values along
the presumptive dorsoventral axis are already defined at pregastrula
stages. In addition, cell lineage-tracing experiments indicate that fates
of cells depend on their position within the early blastula embryo
(Kimmel et al. 1990). Along the animal-vegetal axis, the fate map of the
blastula embryo is rather simple; cells in animal regions of the blastula
embryo give rise to ectodermal fates, while cells from the marginal
regions form endodermal and mesodermal derivatives. A more complex
pattern is observed for the fate map along the presumptive dorsoventral
axis; dorsal animal cells will form neuroectoderm, while ventral animal
cells will form epidermal structures like skin and fins. Of the presumptive mesoderm in the marginal zone, dorsal-most cells will form the
hatching glands and the notochord, dorsolateral cells the heart and
somites, ventrolateral cells the pronephros, and ventral-most cells will
form blood. In this chapter, we will study how positional values within