Animal development 4

Question 1

What are maternal effect genes?

Answer 1

Mutations caused by genes that are dependent on the genotype of the mother
They are expressed in the ovarian tissues during oogenesis

Question 2

What happens when wild-type egg cytoplasm from the head region is injected into a bicoid mutant?

Answer 2

Head segments are generated

Question 3

What is the purpose of bicoid mRNA?

Answer 3

The mRNA is translated after fertilisation to form an a/p bicoid protein gradient
Bicoid protein is a morphogen
It specifies the anterior part of the a/p axis

Question 4

Describe the role of maternal mRNA in creating protein gradients

Answer 4

There is a gradient in Nanos mRNA at the posterior
Nanos suppresses translation of maternal hunchback mRNA in the posterior
Bicoid promotes the production of the embryo’s own hunchback protein in the anterior
Thus the a/p axis gradient in the hunchback protein is established
Bicoid inhibits translation of Caudal protein in the anterior thus forms p/a gradient

Question 5

What is the gene expression cascade?

Answer 5

Maternal genes
Gap genes
Pair-rule genes
Segmentation genes
Selector genes

Question 6

What are gap genes?

Answer 6

Mutations in gap genes cause segment deletions
They are the first zygotic genes to be expressed along the A/P axis
They code for transcription factors
Gap genes and their products interact to define boundaries of expression

Question 7

What do gap genes do to the A/P axis?

Answer 7

The A/P axis becomes divided into unique regions (domains) each containing different combinations of transcription factors

Question 8

What are pair-rule genes?

Answer 8

They are the production of local combinations of gap gene transcription factors

Question 9

What do pair-rule genes do?

Answer 9

The activation of each pair-rule gene in seven transverse stripes along the A/P defines 14 parasegments each pair-rule gene being expressed in alternating parasegments
The mature segments are formed from the posterior region of 1 parasegment and the anterior of the next

Question 10

What are the names of the 2 pair-rule genes?

Answer 10

Fushi tarazu

Even-skipped

Question 11

What are segment polarity genes?

Answer 11

Help to define the anterior and posterior polarities within each embryonic parasegment by regulating the transmission of signals

Question 12

What is engrailed?

Answer 12

A segment polarity gene that is expressed in the anterior region of each parasegment
It is also a selector gene that confers a particular identity on a region by controlling the activity of other genes

Question 13

How is the transcription of engrailed stimulated?

Answer 13

By the products of the pair-rule genes

Question 14

What are denticles?

Answer 14

Small ridge-like features

Question 15

Where are the denticles on drosophila larvae?

Answer 15

On the anterior regions of segments

Question 16

How is the move from parasegments to segments controlled?

Answer 16

A signalling circuit is set up between neighbouring cells to define a segment
The engrailed transcription factor stimulates in the same cells the expression of the secreted protein hedgehog
Hedgehog stimulates the expression of the secreted protein wingless in the cells immediately in front across the parasegment boundary
The expression of wingless and patched (hedgehog receptor) is associated with the anterior part of the final segment
Cells expressing engrailed and hedgehog mark the posterior part
A compartment boundary is a signalling centre that sets up the pattern of cells within the segment later resulting in the formation of denticles in the anterior region