Lecture 13 - patterning the embryo Flashcards
(36 cards)
What creates dorsal/ventral polarity?
a gradient of nuclear localisation of the Dorsal protein:
- High on Ventral side
- Low on Dorsal side
What do the promoters of important dorsoventral genes require?
different level of Dorsal protein need to be activated
Describe the affinity for Dorsal binding sites in the promoters of the snail gene
- Low affinity Dorsal binding sites
- only expressed when a high level of nuclear Dorsal is present
- make MESODERM
What has a high affinity Dorsal binding sites in its promoter?
Rhomboid - in addition it is repressed by Snail
- expressed laterally on both sites of mesoderm
- make NERUOECTODERM
What is a promoter?
a control region in the DNA that controls expression of a gene - it “promotes” transcription
What gene is expressed when there is low levels of nuclear Dorsal?
Rhomboid
What gene is expressed when there is highlevels of nuclear Dorsal?
Snail expressed, interferes with with Rhomboid expression
In the dorsal ectoderm, what does Decapentapleguc (dpp) do?
sets up a second signalling centre on the dorsal side of the embryo
What is the name of the second signal?
Bone morphogenetic protein (BMP)
In what is BMP (bone morphogenetic protein) conserved?
vertebrates
What genes does the antero/posterior gradients of Bicoid and Nanos lead to activation of?
a number of gene encoding transcription factors which are known as GAP genes
What is the primary target of Bicoid & Nanos?
Hunchback gene, which together with Bicoid, sets up the expression of other GAP genes
What do GAP genes create?
a ‘combinatory code’, that defines different regions in the embryo
What GAP genes are responsible for striped pair-rule expression?
Even skipped (eve)
Fishing tarazu (ftz)
What drives the striped expression of the prefigured segments of the embryo?
each stripe is driven by a specific gap gene combination
What are the Pair Rule gene expression stripped known as?
Para segments
What is the effect of the segmentation genes?
go from 7 stripes in a pair-rule gene to 14, as high levels of Ftz or Eve switch on Engrailed
What does high levels of Ftz & Eve lead to?
switches on Engrailed
What directly drives the pattern of the cuticle, e.g. the denticles that form the stripy pattern on the larvae?
The “14-striped” expression of Engrailed and some other genes
What forms the POSTERIOR boundary of the segment?
the future visible segments are formed with the Engrailed positive cells
What has occurred by the time the Posterior boundary of the segment has formed?
the embryo has cellularised - meaning diffusion will not work as no longer a Syncytium.
What has to occur due to transcription factors not being to diffuse anymore, as they are individual cells?
cell-to-cell signalling is required, in order to coordinate the pattern formation within one segment
In addition to the transcriptional regulator (En), what 2 highly important signalling proteins are expressed in adjacent cells?
- Wingless (Wg)
- Hedgehog (Hh)
What are Wingless (Wg) & Hedgehog (Hh) under the influence of?
at first pair-rule genes
- then as a result of a feedback loop, expression of Wg is maintained by Hh, and En+Hh by Wg
