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