Gastrulation- transforming a hollow ball into a 3 layered structure
Learning objective:
1. Formation of ectoderm and endoderm
2. Function of the endoderm in induction of mesoderm/mesoderm-derived tissues
The frog life cycle
1. Gametogenesis
2. Fertilisation
3. Cleavage
- Rapid cell division (mitosis) immediately after fertilisation
- At the end of cleavage, end up with blastula, which is the equivalent to the blastoderm stage in drosophila
4. Gastrulation
- Rearrangement of cells in a specific pattern i.e. ectoderm in the outer layer followed by mesoderm followed by
endoderm.
- cell movement to bring in cells that are supposed to be inside to develop organs
5. Organogenesis- arranging organs
6. Larval stages
7. Maturity
Gastrulation
The 3 germ layer give rise to different organs and tissues,
germ cells do not arise from 3 germ layers
, Both endoderm and ectoderm are specified by maternal cell fate determinants
Animal half expresses
- maternal factors ectodermin
- xygotic factor Fox1e
Vegetal half expresses
- maternal factor VegT + Vg1
VegT specifies the endoderm
- zygotic factor nodal (mesoderm induction)
zygotic factor – is later expressed by the embryo itself
In the dorsal half the maternal cell fate determinant ectodermin is expressed, which represses mesoderm inducing signals
so that mesoderm is only formed at the equatorial zone.
The presumptive ectodermal cells express the transcription factor Fox1e which is necessary for their development.
- Presumptive = in the absence of further information
Maternal factors that set up different region of gene expression in the embryo.
The cells that generate the 3 germ layers are present in the late blastula (zebrafish)
Shortly before gastrulation during mid-blastula transition, transcription is activated in the embryo.
The ectoderm is located at the animal pole and expresses ectodermal markers
The endoderm cells now express endoderm specific genes and secrete factors that induce the cells above them to become
mesoderm.
Yolk cells = Membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk.
- The yolk is made up of many cells called yolk cells.
The egg has polarity before fertilisation
- Dense yolk material in the vegetal pole
- little yolk in the animal pole
Learning objective:
1. Formation of ectoderm and endoderm
2. Function of the endoderm in induction of mesoderm/mesoderm-derived tissues
The frog life cycle
1. Gametogenesis
2. Fertilisation
3. Cleavage
- Rapid cell division (mitosis) immediately after fertilisation
- At the end of cleavage, end up with blastula, which is the equivalent to the blastoderm stage in drosophila
4. Gastrulation
- Rearrangement of cells in a specific pattern i.e. ectoderm in the outer layer followed by mesoderm followed by
endoderm.
- cell movement to bring in cells that are supposed to be inside to develop organs
5. Organogenesis- arranging organs
6. Larval stages
7. Maturity
Gastrulation
The 3 germ layer give rise to different organs and tissues,
germ cells do not arise from 3 germ layers
, Both endoderm and ectoderm are specified by maternal cell fate determinants
Animal half expresses
- maternal factors ectodermin
- xygotic factor Fox1e
Vegetal half expresses
- maternal factor VegT + Vg1
VegT specifies the endoderm
- zygotic factor nodal (mesoderm induction)
zygotic factor – is later expressed by the embryo itself
In the dorsal half the maternal cell fate determinant ectodermin is expressed, which represses mesoderm inducing signals
so that mesoderm is only formed at the equatorial zone.
The presumptive ectodermal cells express the transcription factor Fox1e which is necessary for their development.
- Presumptive = in the absence of further information
Maternal factors that set up different region of gene expression in the embryo.
The cells that generate the 3 germ layers are present in the late blastula (zebrafish)
Shortly before gastrulation during mid-blastula transition, transcription is activated in the embryo.
The ectoderm is located at the animal pole and expresses ectodermal markers
The endoderm cells now express endoderm specific genes and secrete factors that induce the cells above them to become
mesoderm.
Yolk cells = Membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk.
- The yolk is made up of many cells called yolk cells.
The egg has polarity before fertilisation
- Dense yolk material in the vegetal pole
- little yolk in the animal pole
