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The expression of genes in specific regions of the early Drosophila embryo determine the anterior-posterior and dorso-ventral axes of the organism. Expression of these genes are both spatially and temporally coordinated.
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Developmental Cascade of Morphogens
Drosophila melanogaster Development
Gene Expression is Regulated and Much Evolution is Based on Changes in Regulatory Genes
A Few Conserved Signaling Molecules are Used Over in Different Aspects of Development
Cascades of Induction Can Pattern an Entire Embryo or Embryonic Field
Drosophila Early Development is Syncytial
Anterior Posterior Segmentation is Mapped from Syncytial Blastoderm to Larva
Hindgut & Internal organs
Foregut & Internal organs
Anatomical
Gene Exp.
Drosophila Fate Map
Gastrulation Movements
Anterior Posterior Determination
Only 1 gene inactive
Only 1 gene active
White area iscontrolled by Indicated gene
None active
Wt. Bicoid Nanos Torso
Morphogens Are laid Down Durring Oogenesis
The Egg Polarity Gradient Systems
Regulatory Hierarchy of Morphogens
The “Gap” Genes, “Pair Rule” and “Segment Polarity” Genes
Gap Gene Proteins Maintain Gradients By Mutual Inhibition
A) bcd and nos maternal transcripts are tightly localized at the anterior and posterior poles of the unfertilized egg Shortly after fertilization, bcd transcripts are translated, and the resulting protein diffuses posteriorly, generating a gradient; similarly, nos transcripts are thought to generate an opposing gradient of nos
(B) The hb protein gradient then provides a series of concentration thresholds that independently dictate where the anterior Kr, kni, and gt boundaries, as well as the posterior Kr boundary
Nos
Regulation of Even Skipped by Gap Gene Products
Giant and Kruppel Repressors and Knirps and Hunchback delimit expression borders of the even-skipped stripes 3,4, 6 and 7 (see Figure 2, panel C). Two corresponding regulatory regions, 4+6 and 3+7 enhancers encode all sufficient transcriptional information for these four stripes. The eve stripes 4 and 6 are formed in the embryo zones with lower concentration of hunchback and higher concentration of Knirps, conversely the eve stripes 3 and 7 are formed where hunchback concentration is greater than that of Knirps.
Gt & Kr define St 2
Regulation of Stripe 2 Promoter
Stripe 2 Enhancer
Activators Bcd & HbInhibitors Gnt & Kr
Eve expression
Pair Rule and Segment Polarity Gene Expression Effects Structures in Adult Fly
Expression of Segment Polarity Gene Engrailed
Bicoid is a Homeobox Transcription Factor
Dorsal Side is Determined by Absence of “Dorsal” Protein
D
VDorsal proteinConcentrated in nuclei
Dorsal proteinConcentrated in Cytoplasm
Dorsal protein binds to regulatory DNA that turns on mesoderm and nervous system genes and turns off dorsal genes
Protostome vs.. DuterostomeBody Plans
Upside Down and Backwards
Dorsoventral Morphogen Gradients
Presumptive Mesoderm Cells Express the Transcription Factor, Twist
TTime