Biochemistry 3381A Quiz: The dorsal gradient determines tissue specification
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27 May 2020
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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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