Ch9 - Segment Polarity Genes

Question 1

Until now we’ve seen syncytial interactions, now seeing

Answer 1

cells

Question 2

Intercellular interactions mediated by segment polarity genes have 2 tasks

Answer 2

1. to reinforce parasegmental periodicity

2. Through cell-to-cell signalling, cell fates are established within each parasegment

Question 3

The segment polarity genes encode proteins that are

Answer 3

part of the Wingless and Hedgehog signal transduction pathways

Question 4

Only 1 row of cells per parasegment

Answer 4

express the Hedgehog protein

and only 1 row of cells per parasegment express the Wingless protein

Question 5

The key to the pattern of 1 row of Hedgehog and 1 row of Wingless is the activation of the

Answer 5

engrailed gene in cells going to express the Hedgehog gene

• expressed in 14 stripes

Question 6

Wingless is transcribed only

Answer 6

in the row of cells directly anterior to the cells where engrailed was transcribed

Question 7

Once wingless and engrailed expression is established in adjacent cells…

Answer 7

the pattern must be maintained to retain the parasegmental periodicity of the body plan (from pair-rule genes)

Question 8

Maintenance of wingless/hedgehog (engrailed) patterns are regulated by interactions between

Answer 8

cells expressing wingless and those expressing engrailed
• engrailed gene binds Wingless protein
• Engrailed protein activates transcription of Hedgehog in engrailed genes
• Hedgehog –> receptor - express wingless gene

Question 9

*

The Engrailed-synthesizing cells secrete the

Answer 9

Hedgehog protein

Question 10

**

The Hedgehog protein maintains the expression of

Answer 10

the wingless gene in the neighboring cells

Question 11

The Wingless-secreting cells maintain the expression of

Answer 11

the engrailed and hedgehog genes in the neighbors –> stability

Question 12

Engrailed-Hedgehog-Wingless cycle

Answer 12

The Engrailed-synthesizing cells secrete the Hedgehog protein
The Hedgehog protein maintains the expression of the wingless gene in the neighboring cells
The Wingless-secreting cells maintain the expression of the engrailed and hedgehog genes in the neighbors –> stability

Question 13

The Wingless-expressing cells are

Answer 13

within the region of hairs

Question 14

Signals graded as morphogens act

Answer 14

locally to initiate a cascade of local signalling events