FORMING THE NOSE VERSUS TAIL OF A FLY LECTURE 6: FORMING THE NOSE VERSUS TAIL OF A FLY

The Body Plan of a Fly Maggot V Head Thorax Abdomen Tail “Denticle” Hairs Skin Nervous System (inside)

Fly Embryonic Patterning Mutants Anterior-Posterior Patterning Mutants Dorsal-Ventral Patterning Mutants

Hierarchy of Gene Action in A/P Patterning Bicoid Controlled by Mother A P Gap Genes Controlled by Embryo Kruppel Pair-rule Genes even-skipped Segment Polarity Genes (e.g., engrailed) Homeotic Genes (e.g., Bithorax)

Bicoid A P Hunchback Even-skipped 1 2 6 5 3 4 7 Knirps Homeotic

Independent Regulatory Elements Activate even-skipped Expression in Different Stripes 7 1 2 3 4 5 6 even-skipped stripes On Off OtherStripes Coding Region Regulatory Region even-skipped mRNA Stripe 2 Stripe 3

Condition for Activating Expression of even-skipped Stripe 3 1. An activator, which is expressed everywhere, must be present. 2. Repressors, Hunchback and Knirps, must be absent. Hb Kni 3 even-skipped stripe 3

Dorsal-Ventral Patterning Mutants

Hierarchy of Gene Action in D/V Patterning High [Dorsal] Low [Dorsal] No Dorsal Graded Dorsal Concentration Created by Mother Mesoderm Genes Neuronal Genes Epidermal Genes D/V Genes Basic Tissue Types Controlled by Embryo D V

Ventral Epidermal Genes Neural Genes Dpp Neuronal Genes Brk, Sog Dorsal Genes AS-C Rho Ventral Epidermal Genes Neural Genes Snail Neural Genes Twist Mesodermal Genes = M e s o d r m N n - u a l E c t