Morphogens and positional information
3 important questions on Morphogens and positional information
Explain the French flag model
The French flag is used to represent the effect of morphogens on cell differentiation. A morphogen affects cell states based on concentration. These states are represented by the different colours of the French flag. High concentrations activate e.g the 'blue gene;, lower concentrations active the 'white genes' and 'red' serving as the default state in cells below the necessary concentration threshold.
Explain the 'Four Signal model' that is involved in mesodermal induction preceding gastrulation
Two signals originate in the vegetal region
- Signal 1 in the ventral region induces ventral mesoderm at the ventral and lateral side
- Signal 2 in the dorsal vegetal region called the nieuwkoop centre. The induced dorsal mesoderm is called the Spemann Organiser, which is the same as IMZ or dorsal blastopore lip.
Two signals originate in the marginal zone
- signal 2 in the spemann organiser dorsalizes the mesoderm by counteracting signal 4. As a result, intermediate mesoderm (urogenital) is formed.
- signal 4 in the ventral mesoderm ventralises the mesoderm.
- Signal 1 in the ventral region induces ventral mesoderm at the ventral and lateral side
- Signal 2 in the dorsal vegetal region called the nieuwkoop centre. The induced dorsal mesoderm is called the Spemann Organiser, which is the same as IMZ or dorsal blastopore lip.
Two signals originate in the marginal zone
- signal 2 in the spemann organiser dorsalizes the mesoderm by counteracting signal 4. As a result, intermediate mesoderm (urogenital) is formed.
- signal 4 in the ventral mesoderm ventralises the mesoderm.
By which genes is the anterior-posterior pattern in Drosophila determined?
Maternal effect genes: head and tail genes; establisch cytoplasmic polarity
Gap genes: define certain regions in the developing Drosophila embryo. The expression of these gap genes is affected by the concentration maternal genes.
Pair-rule genes: for further specialisation, under control of gap genes. These pair-rule genes have two kinds of genes under their control: segment polarity genes and homeotic genes.
Gap genes: define certain regions in the developing Drosophila embryo. The expression of these gap genes is affected by the concentration maternal genes.
Pair-rule genes: for further specialisation, under control of gap genes. These pair-rule genes have two kinds of genes under their control: segment polarity genes and homeotic genes.
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