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Axis Specification I. The Maternal-Effect Mutants. (also found the D/V Group). Nusslein-Volhard, 2004. bicoid mRNA oskar mRNA protein + nanos RNA. microtubule-based - + . A-P polarity set up in egg chamber. maternal.
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The Maternal-Effect Mutants (also found the D/V Group) Nusslein-Volhard, 2004
bicoid mRNA oskar mRNA protein + nanos RNA microtubule-based - + A-P polarity set up in egg chamber
maternal The Maternal A/P Information BCD is a transcription factor and a translation factor (represses Caudal translation) NANOS is a translation factor (represses Hunchback translation) The Terminal System BCD NANOS
The Zygotic Genes Nusslein-Volhard and Wieschaus, Nature 1980 Wieschaus Nobel Lecture, 1995
Creating Complex Patterns From Simple Ones maternal zygotic BCD Gradient GAP Genes HB = Red, KR = Green Pair Rule Gene (fushi tarazu) Segment Polarity (engrailed)
Complex Patterns From Simple Ones: Gap Genes BCD Giant Kruppel
Creating Complex Patterns From Simple Ones 3 Maternal “Systems” for A/P maternal zygotic ≈11 Gap Gene Domains 8 Pair-rule genes x 7 stripes = 56 domains ftz eve
Generating Precise Positional Information Along Axes Dave Kosman
Understanding Transcriptional Control of Patterning: The Story of eve Levine and colleagues eve is a pair rule gene--expressed in 7 “stripes” How is this pattern created? Step 1: “Promoter bashing” to identify relevant enhancers ftz eve eve Stripe 2 enhancer--lacZ S. Small eve Stripe 3/7 enhancer--lacZ
Studying Transcriptional Control of Development Step 3: Use biochemistry to identify direct regulators Eve Step 1: “Promoter bashing” to identify relevant enhancers Step 2: Use expression patterns and genetics to identify candidate regulators eve stripe 2 Gt Step 4: In vivo proof: mutating cis binding sites should cause same change in expression as mutating trans regulators Kr Small, Blair and Levine EMBO 1992
Eisen Lab PMID: 18584029 Sepsidae (scavenger flies) ≈100 mya
Eisen Lab PMID: 18584029
Eisen Lab PMID: 18584029
Positional Information in the Embryo Controls: Segment Identity (Making Segments Different From One Another) Segmentation and Pattern Within a Segment
Wg Hh Segment Polarity Genes -wg and hh Signaling Pathways -Establish 14 Segmental Boundaries -Act as morphogens to pattern within each segment
Positional Information in the Embryo Controls: Segment Identity (Making Segments Different From One Another) Segmentation and Pattern Within a Segment
Fun with Flies! Homoeosis (Bateson 1894): alteration of one organ of a segmental or homologous series from its own characteristic form to that of another member of the series “homoeotic mutants” Ultrabithorax Antenae to Leg Leg to Antenae Proboscis to Leg Haltere to Wing Wing to Haltere Genitalia to Leg Ed Lewis
Homeotic (Hox) genes are expressed differentially along the A/P Axis Specify segment identity
Drosophila Mouse
Drosophila Hypothetical common ancestor Amphioxus Mouse
Regulation of Segment Identity by a “Hox Code” Wild Type T2 T3 Antp ON Antp OFF Ubx OFF Ubx ON Wing Haltere Ubx mutant T2 T3 Antp ON Antp ON Ubx OFF Ubx OFF Wing Wing Ultrabithorax Wing Haltere UBX Expression
Mammals Are Segmented Too Cervical Thoracic Lumbar Sacral
5/6 mutant Triple homozygote A/a C/c D/c X A/a C/c D/c 1/64 pups = aaccdd Hox Genes Specify A/P Identity in Vertebrates Wellik and Capecchi, 2003
Patterning the Dorsal-Ventral Axis Maternal-Effect Mutants: The D/V Group D wt P A V Dorsalized Ventralized
A. Courey D/V Patterning Establishes the Mesodermal Identity Determined by twist and snail Toll pathway: on on ventral side
It is not birth, marriage or death, but gastrulation, which is truly the most important time in your life. - Lewis Wolpert (1986) Gastrulation
Drosophila gastrulation The mesoderm and endoderm invaginate separately (a bit unusual) Ventral View
? Cell Biology Cell Division/Death Cell Adhesion Cell Movement Cell Shape Cell Adhesion and Cell Sorting Cell Identity Morphogenesis
The Cell Biology of Fly Mesoderm Gastrulation Epithelial-mesenchymal transition (EMT) Apical constriction Invagination Migration/spreading
folded gastrulation and concertina Effect Apical Constriction twist and snail folded gastrulation (ligand) Apical constriction fog expression in mesoderm is dependent on twist and snail GPCR? Concertina(G alpha) RhoGEF
Rho Kinase myosin Myosin relocalizes from basal to apical at the time of apical constriction Apical constriction folded gastrulation and concertina Affect Gastrulation twist and snail folded gastrulation (ligand) T48 GPCR? Concertina(G alpha) fog RhoGEF
DE-cadherin May Regulate EMT in the Drosophila Mesoderm Epithelial-mesenchymal transition (EMT) snail DE-cadherin EMT
How Cell Identity Controls Morphogenesis of Gastrulation Cell Identity (twist, snail) fog, T48 FGF-R Cell Adhesion E-Cadherin? Migration Epithelial-mesenchymal transition (EMT) Apical constriction