Axis formation and segmentation in drosophila
Learning objectives:
1. How do cells become different from each other during development?
2. How do cells separate populations to form organs?
3. What happens if these mechanisms are affected?
The life cycle of drosophila melanogaster
1. Female + male
2. Embryo
3. 1st instar larva
4. 2nd instar larva
5. 3rd instar larva
6. Prepupa
7. Pupa Metamorphosis occurs to form pupa
Pattern formation: events that determine the spatial organisation in the developing organism
Image shows:
- Germ line cells- posterior end
- Development has different stages from genes, cells, population
- Can tell a lot about development at the embryo stage
,The early embryo of many insects consists of 1 large cell with many nuclei: syncytium
Stain cells to make structure visible
Staining of nuclei
No cell division
Division of nuclei in early embryo
Nuclei migrate to the periphery
Cell membrane appear between the nuclei at the boarder- stage 10
Can draw fate map at blastoderm stage
All cells that end up in the anterior region will form the head
Blastoderm stage = single layer of cells
Can tell what the cells will function as
Key events of embryogenesis occur in the syncytial blastoderm stage
1. Pole cell formation and migration
- Pole cell = germline cells- pass on genetic information to next generation
2. Determination of the anterior- posterior and dorsal- ventral axes
3. Segmentation
- Subdivision of embryo along the anterior- posterior axis
Formation of the A-P axis: egg cytoplasm is not uniform
Factors unevenly distributed in egg cytoplasm
, Morphogens form a concentration gradient
Morphogen= chemical agent able to cause morphogenesis as present in a concentration gradient
Anterior to posterior gradient morphogen: Bicoid
Bicoid is a maternal-effect gene that is important for establishing the anterior of the fly embryo
Bicoid is a protein morphogen necessary for formation of anterior structure of the larva
- Anterior structure = head and thorax
Bicoid mutant head
- No Bicoid = no head structure instead 2-tailed structure
- Bicoid stands for 2-tailed
Experiment: Bicoid is required for formation of head and thorax
Took some cytoplasm from the anterior region of wild-type egg and place into the anterior region of Bicoid mutant
egg = some anterior structure developed
Took some cytoplasm from the anterior region of wild-type egg and place into the middle region of Bicoid mutant egg
= formation of head structure middle region of larva.
- This experiment shows that Bicoid has a morphogen gradient
Same experiments for other morphogen molecule i.e.
- Hunchback
- Nanos
- Caudal
Learning objectives:
1. How do cells become different from each other during development?
2. How do cells separate populations to form organs?
3. What happens if these mechanisms are affected?
The life cycle of drosophila melanogaster
1. Female + male
2. Embryo
3. 1st instar larva
4. 2nd instar larva
5. 3rd instar larva
6. Prepupa
7. Pupa Metamorphosis occurs to form pupa
Pattern formation: events that determine the spatial organisation in the developing organism
Image shows:
- Germ line cells- posterior end
- Development has different stages from genes, cells, population
- Can tell a lot about development at the embryo stage
,The early embryo of many insects consists of 1 large cell with many nuclei: syncytium
Stain cells to make structure visible
Staining of nuclei
No cell division
Division of nuclei in early embryo
Nuclei migrate to the periphery
Cell membrane appear between the nuclei at the boarder- stage 10
Can draw fate map at blastoderm stage
All cells that end up in the anterior region will form the head
Blastoderm stage = single layer of cells
Can tell what the cells will function as
Key events of embryogenesis occur in the syncytial blastoderm stage
1. Pole cell formation and migration
- Pole cell = germline cells- pass on genetic information to next generation
2. Determination of the anterior- posterior and dorsal- ventral axes
3. Segmentation
- Subdivision of embryo along the anterior- posterior axis
Formation of the A-P axis: egg cytoplasm is not uniform
Factors unevenly distributed in egg cytoplasm
, Morphogens form a concentration gradient
Morphogen= chemical agent able to cause morphogenesis as present in a concentration gradient
Anterior to posterior gradient morphogen: Bicoid
Bicoid is a maternal-effect gene that is important for establishing the anterior of the fly embryo
Bicoid is a protein morphogen necessary for formation of anterior structure of the larva
- Anterior structure = head and thorax
Bicoid mutant head
- No Bicoid = no head structure instead 2-tailed structure
- Bicoid stands for 2-tailed
Experiment: Bicoid is required for formation of head and thorax
Took some cytoplasm from the anterior region of wild-type egg and place into the anterior region of Bicoid mutant
egg = some anterior structure developed
Took some cytoplasm from the anterior region of wild-type egg and place into the middle region of Bicoid mutant egg
= formation of head structure middle region of larva.
- This experiment shows that Bicoid has a morphogen gradient
Same experiments for other morphogen molecule i.e.
- Hunchback
- Nanos
- Caudal
