Biochemistry 3381A Quiz: The dorsal gradient determines tissue specification

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The dorsal gradient determines tissue specification
Cells that are exposed to a high concentration of Dorsal become mesoderm. Dorsal activates genes
that create a mesodermal phenotype
the dorsal gradient regulates a complex pattern of gene activation and inhibition that determines
tissue fats
Relatively little is known about the
formation of the left-right axis, however the
microfilament cytoskeleton is involved
The anterior-posterior
specification
Bicoid and
Nanos are the most
important maternal morphogens that control polarity
Experiments showing that Bicoid is responsible for the development of
head structures in Drosophila
Bicoid blocks expression of caudal
Bicoid activates expression of hunchback
Nanos blocks expression of hunchback
Bicoid and Nanos control the expression of caudal and hunchback mRNA. Bicoid, Caudal and
Hunchback act as transcription factors that activate or repress zygotic genes
Bicoid acts as a morphogen that determines cell fate in a concentration-dependent fashion
High concentration of Bicoid: Anterior head structures
Slightly less Bicoid: Jaws
Moderate concentration of Bicoid: Thorax
No Bicoid: Abdomen
The promoters of the target genes have different affinities for Bicoid: The more anterior the
expression, the lower the affinity
Development of the unsegmented body ends (acron: terminal portion of the head and telson: tail) is
controlled by the terminal gene group
The most important of these genes is torso
The Torso protein activates a cascade that inhibits Groucho
Groucho inhibits the expression of tailless and huckebein
If groucho is inhibited, tailless and huckebein are expressed
These two genes specify the termini of the embryo
If Tailless and Huckebein protein act alone, a telson is
formed
If Tailless and Huckebein act in the presence of Bicoid, an
acron is generated
Specification along the axes
Once the anterior-posterior and dorsal-ventral axes are
established, they can be used as a coordinate system to
specify positions within the embryo
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